The AM Forum

Hola !

I have a few matching questions...    let's compare an open wire fed antenna that is coupled to 50 ohm coax thru a link coupled tuner  -  compared to a simple coax fed antenna.  Let's say both are matched at 1:1 swr.   If the antenna link coupled tuner is NOT adjusted again, will it have more, the same or less bandwidth than the straight coax fed antenna?

For example, if both antennas were previously adjusted to 3.800 MHz at 1:1, if the input frequency of both is moved to  3.900 MHz, which antenna system will show the best broadness (lowest swr) without adjustment?

Also, how about tapping the openwire with a current fed balun using ferrites and finding the 50 ohm tap on the openwire?  How does this compare to a tuner or straight coax for bandwidth?


If the openwire impedance into the tuner is say, 800 ohms, J0, and the coax is 50 ohms, I would think that this is a high Q / high impedance transformation, thus a narrower bandwidth without changing the tuner.   In contrast, a straight 50 ohm match to the dipole is of lower Q and will give a broader bandwidth??

I am feeding a two element delta loop array with both elements fed with openwire. Both openwire feedlines come to the ground. One is the driven element and the other is the reflector using a shorted stub for tuning F-B. The link coupled tuner is outside at the base of the tower, so once set, I cannot adjust it from the shack.  I need a reasonable bandwidth between 3780 and 3890.   (about 110 KHz)

Also, my feedlines are VERY long, like up tp 450', (and potentially expensive) thus the desire for openwire on some of the higher gain antennas.

Another local dipole antenna uses a simpler match with a straight dipole, but in this case uses a ferrite current balun tapped to the openwire 50 ohm spot. (no tuner)

For these two openwire antennas, before proceeding, I want to probe deeper about the best bandwidth choice as discussed above.

Any opinions?

T

Coass cable has higher loss.  Ergo, the reflected waves will be lower with coasshole cable.

Which will broadband the swr curve.

--Shane
WP2ASS / ex KD6VXI

Hi Shane -

OK, then let's say for discussion purposes that the coax is super low loss hardline with about the same loss as the openwire.   Then how would the bandwidth compare between using the openwire with a tuner vs: direct low loss hardline?     I'm trying to figure out if using a high impedance openwire output with a 50 ohm link coupled tuner will have narrower bandwidth than a simple low impedance coax antenna - assuming no tuner or coaxial dipole adjustments are made after the original frequency is moved....

T

A lot depends on the loaded Q of the link coupled tuner also, Tom. If it's a high Q obviously the bandwidth will suffer.

Tom,
As Shane points out, just because something looks wide band does not mean that it is efficient as a radiator.
I built a 75 meter variable ratio helically wound vertical in 1974  for my Dodge Dart. I used some 5/16 diameter fiberglass bike flag pole that was 6 feet long and I added a 2 ft piece of aluminum tubing to the top for a capacitive hat.
It covered 3850-3925 with less than a 1.6 VSWR and I comsidered myself and antenna genius….😉😂😂
It did work, but later I figured out that only a small part of the energy was actually being radiated…. Life is full of disappointment to the young and full of skepticim to the old and cranky…😉

Any tuned link coupler will be narrow band unless it has a lot of loss.
If it is important to reduce harmonic energy, and transmit the maximum power also, that is not an option.

Designing it to be easily retuned by presets for different frequencies can make it efficient in every way, however.

If, however, you want the broadest coverage at low loss, then 7/8 heliax feeding a cage vertical might be a good option.
Cage verticals are a kind of discone antenna I think. They are inherently low Q and can cover a 10:1 frequency range, I understand, with some tweaking if match for wide band use.

No panaceas, though- every design requires a compromise of some sort.


https://www.qsl.net/dl5aza/infreuse.htm

https://www.tc2m.info/TC2M%20HF%20Vertical%20G8JNJ.pdf

I look at this as the student talking to the master. I think it was Jerry Sevick, W2FMI(SK), who said, "A compromised antenna will give you a compromised signal." Now, how much compromise can you tolerate? I've been kind of watching this thread evolve because I am looking to do something very similar. I want a short length of RG213 to a remote antenna tuner which will feed the antenna with 600 ladder line. The control part is supposed to run by an Arduino so that when I need to change bands, I can access a memory point in hopes that my antenna is tuned to the proper band segment again. This has been previously discussed in a prior thread especially using a balanced line tuner. I was on the fence with using the coiled coax as a balun prior to connecting to the tuner where everything is (hopefully), balanced, or using ferrite beads or even possibly a 1:1 balun, (or unbal in this case) on a toroid. Somewhere along the line you will suffer some sort of signal loss. I would read up on some of the literature from L.B. Cebik, W4RNL(SK), his observations are still available on the internet. Also E.F. Bigbie W4MMQ(SK) promoted the L-tunerX2 that Rich Measures popularized. I cut this from the KW Matchbox thread from Fred, KC4MOP: http://ka4cid.blogspot.com/2008/12/w4mmq-legacy-balanced-antenna-tuner.html Sorry for the ramblings Tom. I like to give as much information as I have!

Excellent comments  Mike, Buddley and Mike(y).   Thanks.

Yes, probably a broadbanded antenna like a three wire or even a horizontally ploarized discone would do the job for broadbanded coverage for local reference antenna 75M work.  I once had up a three wire dipole in the winter. It was so heavy that the ice destroyed it.   So I'll build a single wire #10 wire dipole as a compromise. Not sure if I will use openwire on coax yet for it.

For the 75M delta loops, I am using a link coupled tuner (pictured) and 14" spaced #10 openwire.   No spreaders for both the driven element or reflector.

Yes, I think you are all correct about the shaper tuning antenna matcher producing a narrower bandwidth without retuning.   I might look into your Arduino remote tuning idea once it is running and solve the narrow tuning problem.

BTW, Micke(y)... I don't mind asking the dumb questions and sounding like a newbie.  I've forgotten a lot of what I have learned - or maybe never learned it in the first place. As long as there are some guys who learn from my threads I am happy. Acting like a know-it-all is not my style.  I can take the heat...  I tend to focus on only what interests me intensely and ignore the other stuff which can leave some knowledge gaps, but that's OK until it's needed.   ;D

Here's some pics of what I've been doing here:

T

Pic #1:  75M delta loop antenna matcher - I will solder the connections on once finalized.  I ordered a 24 gallon large plastic tub to cover it for the weather.  I added a coil center tap to ground. It balances perfectly with no change to swr in the exact center. Suggest link coupled tuners of similar floating design out there add the CT to ground for balance.

Pics# 2 and #3:  Look closely and see the delta loops and wide-spaced feeders spread between 120' / 190'  - but are hard to see in the sunlight.   No spacers means less loss and virtually immune to weather effects. Also mounted on this tower is a 40M  wire dipole at 55' and a second one at 110'. They fill in the TO angles quite well.   

Pic # 1:  The local reference dipole at ~ 100' will be hung flat between these two towers.

Pic #2:  This is the new link coupled tuned to drive the delta loop's driven element with SWR 1:1 at 3795, the DX window for 75M.

Pic#3:   Testing -  a simple method of tuning the reflector from the ground with a stub and short.  I use a beacon 1/4 mile out in the woods to generate a signal off the back and null it into the noise. At zero degrees TO angle it still works quite well for testing.  An MFJ-259B analyzer set to "always on" generates a strong 100 mW signal with a small 13.8V 54 AH battery.

Tom,
If you read the articles on the cage verticals, you will see that the author says that 3 wires is an absolute minimum and then you will have swr spikes across a wideband sweep. 8 wires or more are needed for good broadband response.

By the way- I have probably read and profited from dozens of your threads going back almost 20 years on here. I doubt anybody who can read considers you a “newbie” 😉😂😂😂
One of the things I like about you is that you are always thinking if new ways to look at problems and designs and that draws out not only chuckle headed responses, but lots of very smart ideas based on the experience of all the great Engineers and builders that lurk on this Forum.
Once a guy thinks he knows it all, he has stopped growing and started
Annoying others.
I like to draw people out
Myself because so much of what I used to “know” turned out to be false and
Half baked.
I was licensed in 1964 and have my own areas of past experience, but in AM I consider myself a newbie but I like to know more when I learn something new and there I’d always more.
It would be boring if this were not true. 😉

Many decades ago I ran an 80 meter setup with two dipoles in parallel at the feedpoint, fed with open wire line to a link coupled matching network.  The dipoles were purposely made different lengths, run 90 degrees to each other  and one was flatter and the other was more of an inverted V configuration, based on what trees were available.  I don't recall which was which, nor what the length difference was.  I found a tuning point that gave me a pretty nice double SWR dip well over 100 khz apart, in places where I wanted it..  And of course I could run it around the band further with a twist of the dials.  I didn't keep notes on what I did, but it was cheap and cheerful and worked well.
The Shively Labs 6015 FM panel antenna, of which I tuned many over the years, was built similarly, but with both radiators in an inverted V setup, over a mesh panel.  Tuned properly, different lengths on the dipoles, I could measure current phase and amplitudeson the radiators that indicated perfect circular polarization.  toward the horizon.  Three of them around a tower made a nice omni pattern.  Perhaps my gumped up dipole setup did similarly, although it was more likely some version of elliptical polarization, firing straight up.  It did indeed  seem to have less fade than the dipole it replaced.  I just built it with bandwidth in mind.
73 de Norm W1ITT

Interesting comments, Mike -

There's a listing that shows the active thread hits on all of the threads on this BB.  There are thousands of hits each day from the internet. Some of these older threads show 10's and even 100's of thousands of hits over years, mostly from guests to this site doing a search on Google type search engines. The readership of this AM Fone is tiny in comparison.  Check out the link on this site under "Users on Line"

"98 Guests, 4 Users (1 Hidden)"

Interesting reading some of the old threads that pop up every day.


ALSO:

I might use 75 ohm coax from the "local" 75M dipole reference antenna to the 75 ohm hardline.  This would be a 150' run to the hardline and then 125' to the shack.  I am looking at this very inexpensive RG-11 Tri-shield 75 ohm coax at only $86 for 500' -  shipped. It is direct burial.  I think the center conductor looks a little light and the three outer conductors will need a clamping lug, no soldering..  Copper clad steel inner for soldering. Will this stuff handle a 1K AM signal on 75M?   It uses a "gel" for moisture I think. Any problems with that and RF?

It will use a W2DU style ferrite balun at the feedpoint.  Coax will allow me to adjust the dipole height to anything between 110' to 60' for local optimization.

I have used it years ago and never had a failure and the loss seems comparable to RG-213...  

CHECK OUT for 75M use:

https://www.ebay.com/itm/114776635273?hash=item1ab9387789:g:iJMAAOSwzeBggG6E


"This LOGICO RG11 60% Tri Shield Direct Burial Gel Flooded cable is designed specifically for Outdoor/Direct Burial/Aerial use. The gel-filling protects the wire from moisture, making this cable ideal for wet or humid areas. RG11 cable has proven itself as the standard for CATV/SMATV/CCTV installation with bandwidth to handle the demands of today’s HD signals.

RG11 Tri Shield 14AWG Direct Burial/Gel Flooded Cable
CCS (Copper Clad Steel) Conductor 75Ohm/3.0GHz
1st Shield Bonded Aluminum Foil - 2nd Shield- 60% Aluminum Braid Shield - 3rd Shield - Al/Pet/AL FOIL
LDPE Jacket with UV Resistance
500 feet (176 meters) Black Jacket / Wooden Reel"
 
T

Somebody gave me a 500 ft roll of this direct bury RG-11.
The foam looks great, so dialectric losses will be pretty low at HF and if the line is flat, no danger of arcing over.
I did some calculations on the center conductor loss because of the steel core.
The spec that I could not be sure of is the thickness of the copper.
It is likely only a few mils, I am guessing.
I don’t have my figures, but skin effect above 10mHz is quite pronounced, so almost all the current will be carried by the copper plating and at 75 ohms, current will be lower than at 50 of about 20%.
The frequency range commonly specified is 5Mhz to 3Ghz, so I was unable to find attenuation data at 160 and 80 meters.
You could just run a set amount of power into the 500 ft roll at 160 and 80m and have a Bird going in and a Bird and a dummy load st the other end.
After you see the power loss, you can get an idea whether the stuff will be an efficient transmission line at 160 and 80M.
At 40 and above, dialectric losses will rise slowly and copper losses drop, I think.

This is like a Doctor prescribing a drug off label. Nobody expected anyone would use this stuff for low HF, so they used steel for the core.
If you run these tests, you will have real data and I would love to know the answer about 160M and 80M long runs.

As far as traffic- being a nerd my whole life, I was always in a smaller crowd than the cool and sexy people, so my Facebook account is for seeing pics of my grandchildren and I don’t have an Instagram account and Twitter promotes unfiltered idiocy, so sure- we are a small (weird?) bunch of outliers who care about something nobody else cares about until they need our expertise to keep their babble flowing. Ome thing I have in common with the mob on social media is I don’t care about much they care about either….😉
Let me know if you run some attenuation tests on that 500 ft roll at 160 and 80 so I can decide whether to use it myself…😉😁

OK on the RG-11, Mike.   That report is actually better than I expected, so I might order a roll if we continue to get neutral opinions.

As I mentioned, I used some years ago and it held up fine to a 75M AM KW.  The only problem I had was using RTV for weather proofing and after 5 years RTV breaks down and blows away in the wind. I lost the whole RG-11 run due to water damage.   I also wonder how well the shield can hold up to a vertical 100' drop without stressing the shield.  I see some RG-11s use an internal messenger cable, but not sure if this type does or not.  It certainly is light cable, which is good since I cannot support the center and must include a ferrite balun.  I see some installations that use an external rope messenger cable to support the center above the dipole. Like an overhead truss.  This is clever.

These days for waterproofing I am using the Scotch 33 super flex tape and a layer of 3M TemFlex  rubber splicing tape. I might also add some liquid tape on top of all that. I saw a few You-Tube videos as well a DX Engineering videos about using these products.  I think water and coax are the biggest [contamination] problems of all.  I've replaced all my outside coaxes after 13 years now OR using open wire.  The 75 ohm  hardlines in underground pipes to each tower are all OK.  These are about  1/4 the loss of the RG-11 being about 0.1 dB loss at 5 MHz.

I may order some RG-11 within a day or so unless I get any heads up warnings about the stuff.   The only real issue I see with it is the inability to solder to the shield, being alum, etc.  I plan to use crimp on silver plated lugs, nuts and bolts, with heavy waterproofing. Lugs and bolts worked well before.   It is good for UV according to specs. No direct burial plans here.

Anyone have comments on RG-11 direct burial stuff before I plunge for $86?

T

WeatherProofing coax splices video:

https://www.youtube.com/watch?v=CcHiHCw0lsY

Comment on using direct burial coaxial cable:
If any part of it is exposed, do not run over it with a mulching lawn mower.
73 de Norm W1ITT

Tom,
The fact that the coax core is 14 gauge steel likely makes hanging it safe enough, though bends are hazardous due to migration in the foam, so big curves or keep it straight, I think.
One possible way to reinforce it is running some 3/16 or 1/4 Dacron  braided line parallel to the RG-11
You could shrink some inner melt shrink on every foot or so to hold the coax up.
Black cable ties over that would buy enough integrity for a few years.
The Dacron will last a number of years and can carry hundreds of pounds with little stretching too. The black UV resistant stuff is not expensive in 500 ft rolls.

https://www.amazon.com/500-Dacron-Polyester-Black-Cord/dp/B00ZJ6LKA4/ref=sr_1_1_sspa?crid=3ELLQKU4BVC4P&keywords=3%2F16+dacron+polyester+rope&qid=1657223657&sprefix=3%2F16+dacron%2Caps%2C231&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExME8wNUc0V05DMlY0JmVuY3J5cHRlZElkPUEwMDk5Nzg0M0xNVzQ2UUtLUUtOUSZlbmNyeXB0ZWRBZElkPUEwMTA5MzQ4MlRIRldOQlBFWFdEJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

https://www.amazon.com/Black-Dacron-Polyester-Rope-500/dp/B01K2781RO/ref=sr_1_8?crid=3ELLQKU4BVC4P&keywords=3%2F16%2Bdacron%2Bpolyester%2Brope&qid=1657223657&sprefix=3%2F16%2Bdacron%2Caps%2C231&sr=8-8&th=1

Tom, when I worked at B&W over 32 years ago, we used a special heat shrink that had a sealant in it. It was good for using in our cooling pools when we would do an ultrasound inspection on nuclear cores. It would set up like an RTV but it wasn't as pliable, (semi-rigid). Fast forward to today where I see there are tons on Amazon. You might want to consider using something like that. Then I would cover the splice/joint with rubber splicing tape which vulcanizes over time, and as an added protection use just regular black electrician tape for the whole kit and kaboodle. YYMV!

Mike and Mike(y):

I picked up  3' each of the 1" and 2"  3:1 adhesive  heat shrink.  I've used this before and it is quite strong and seals well.  The TemFlex rubber sealant tape and Scotch 33 laid over it will work FB.

The 500' spool of RG-11 is on its way too.  There are a lot of advantages to my using it... one is lightweight to support with no center support. Another is 75 ohms which will match my exisiting underground hardline and is a decent match for a higher dipole. Also it's the cheapest coax out there. I can make it work with the connections.

I got the dipole up in the air today but with no feedline. I chose to hang it loosely with the ends at 105' and the center at about 95'. I could make it flat by tightening it up somewhat. Rope and pulleys from the ground. Height is a good choice for local and moderate distance antenna for 75M.  It will complement the delta loops array.     I can now get rid of my old inverted V with the intermittent connection / water damaged coax..

Thanks for the help and advice!

T

Just like a spider web.  If you look real closely at pic #1 and #2 below, you can see the new copper #10  75M dipole stretched between the two towers.  Just below the picture center, left to right.  That dipole is at about 100' high and needs a feedline, just rope feedline right now...   Many of my dipoles end up being inverted Vees.  I get a good feeling when a dipole is flat.  ;D

The three rotary "gates" on the left 120' Rohn 45 tower are waiting for another project... triple stacked homebrew 2el aluminum 20M Yagis at 33', 66' and 99'.  I might as well use the same RG-11 coax for the job. Same as the 40M array.... like coffee but spelled differently.

BTW, climbing over those star-guyed frame assemblies is scary stuff.  There's three to contend with going up and then going down. It would pay to be 6' 3".

Just curious what you are using for antenna wire, Tom?
The RG-11 you are using is only about 1.4 oz/ft, I think (80lbs/kft)
So the coax will just be pulling down less than 10 lbs on the center.
With the center 10ft below the ends, the stress on the wire is about 6-7 times that weight plus the added weight of the insulators, etc, but in icing conditions, it could be much higher with that thick coax loaded with a collar of ice plus winds.
That drop down is essential. The tangent function makes the linear stress ballon at near actual flat to an undefined value. Just pulling it up 5 feet to a 5ft sag makes the linear pull 12 times or double the 10ft sag value.
The stress is shared, however from each side of the “triangles”, though it is still considerable and copper will not do, I think, unless you truss it with dacron spars with your 10ft drop and then make the antenna “flat” at 95 feet. 3/8 Dacron needed
, likely …
10gauge copper weld might be a good choice. Good for over 1000 lbs, I think.

Good 10gauge copperweld will have about 6-7mils of copper jacket I think.
Avoid cheap stuff with less than 3mils at 75 and 160meters…

Using a horizontal double element can help make it broader plus share the load and stabilize it laterally too. Just thoughts…

Good ideas Mike, and I think I will use some of them.

I'm using #10 insulated EHHS  Home Depot wire.

Since I may need more physical strength in the dipole to better hold up the feedline during ice, etc.,   AND a better broadband swr curve, think I will consider using TWO wires in a cage dipole config.  I could put simple spacers, maybe fiberglass, just at the dipole ends.   The spacers could be pretty wide, (fan dipole style) like 24" to give a broadband effect. The spacers will be near each tower so the weight load is less.

I wonder if this will improve the  swr bandwidth much on 75M with only 2 wires in the "cage?"    

A friend suggested that I try a 10' spaced fan dipole using a second set of ropes. (two similar dipoles fed at the center)  I wonder if that will enhance the bandwidth even more or create diminishing returns?

BTW, I'm looking to cover 185 KHz, from 3885 to 3700 with an swr below 2:1 if possible..

T

cold shrink
https://www.powerandcables.com/product/cold-shrink/cold-shrink-tubes/

Tom,

I like the double wire idea. I am going to use a design from the 2nd Antenna Compendium that uses two wires to get much better bandwidth.
See pic below: bottom of post.

Pure copper wire not strong for its weight. It will be fine untill you get a bad ice storm that will make the weight born multiply a lot and only steel will stay ther and not stretch out or break.
You could run some Dacron rope between the pair of wires to carry the weight, though, if you must have pure copper wire.

40% copperweld means that 40% of the weight of the wire is copper or about 36% of body.
That comes out to be about 10 mils of copper sheathing, so awg10 40% copperweld is as good as pure copper at most RF frequencies we use plus some extra.

It is pretty stiff so you need to shrink the end and put through a 1/8 SS thimble and then solder a flexible multi-strand THNN wire to the end and  wire wrap the part coming out of the thimble and shrink it so you have a flexible wire to make the connection without scarring the copperweld.
You can also use a nice porcelain strain insulator to give you a nice radius to prevent any kinks instead of the thimbles. Thimbles work well for HDPE center insulators, though and make it at least 1/4 inch thick or more. It is very stiff and strong if thimbles spread the stress.

Here is a skin depth calculator to see how thick copper needs to be at any frequency you choose:

https://daycounter.com/Calculators/SkinEffect/Skin-Effect-Calculator.phtml

For awg10, the depth is 2 mils at 2mhz

Here is where I got my 10awg 40% copperweld.
Avoid cheap knockoffs, though….
73, Mike

https://www.daburn.com/2386DaburnCopperweldWire.aspx?gclid=CjwKCAjwq5-WBhB7EiwAl-HEklNRRbRkKtfM56ITdZzQslmN1i6gVLe0deayCuajTqKxG0C-uDMW6BoC0UMQAvD_BwE


The spacers for the Fat dipole can be made with 5/16 weather proof fiberglass rods.
You can get them at farm supply stores pretty cheap. They are white and pretty smooth, but I scotchbrite them to get rid of random glass fibers that keep on giving pain if they get under your skin…😬😉

I got some 6ft rods so they are long enough for the 160m version and can be cut down fir 80 meters.
This antenna is height sensitive fir impedance match, but you are already planning to make that available to find the optimum values. Lengths and spacings could be varied to optimize at a given height, but this antenna will like the 75 ohm feedline at 100’ I think.

Hi Mike -

The amazing bottom line is that the "Fat Dipole" will produce a 1.6 : 1 or less swr between the whole 3.5-4.0 MHz band!  That is amazing.    3' spacing between wires is pretty big, but that result is impressive.  In that case maybe my goal of 185 KHz bandwidth could be kept to under 1.3 :1 ?

If that were a regular single wire dipole with results like that, I'd think the coax was contaminated with water.  ;D

The copperweld is the right way to go, but think I will try it first with the #10 copper that I have available.  I will keep the Fat Dipole rather loose and feel it out.  Usually in the winter I loosen up some of my antennas expecting ice storms.

Making it as light as possible will be the goal.  I found a way to support the coax at 25' above the ground with a small mast - so the vertical unsupported drop will only be  70' or so for the RG-11.  I may not use center 3' spacers - just 3' spacers on each dipole end closer to the tower which should help lighten things too.   I'll have to think more about keeping the whole assembly from twisting in the wind. Maybe the 3' center insulators are needed to prevent twisting?

I was thinking of replacing the 1:1 "balun transformer"  with a string of large ferrite beads.   I will tie the cores and feedline to the center insulator for support.  Keeping a sag in the dipoles will help reduce the stress a lot. There is plenty of height to work with.

I'll give it some more thought and once I get something working I'll let ya know the results.  I may hoist a few prototypes up there first to see.

Tnx for the info, OM!

T

Tom,
I had not thought about the balun in this context, but an effective choke will need two FT-240-31 wrapped with 16 turns of rg-400 and that must be weatherproofed I think, though guys let those things be out in the weather all the time.
Maybe you may wish to opt for an old school 1/4 wave folded tuned stub which will take about 65 feet of the RG11 coax.
I used these a lot in
My youth at all frequencies.
You can add a good choke balun at the bottom I think if you are concerned about common mode current at the ends if the band where the stub impedance will drop down.
You may be able to make the stub from Rg-6 snd it will be even lighter.
Remember- velocity factor is not considered because the folded stub is an air dialectic 1/4 wave stub.

This is a problem that I myself have been working on, so I am anxious for your results.😉

Mike,

I will use just a string of ferrite cores on the coax at the feedpoint.

I have most of it planned out except...


Question:  I'm trying to get a handle on how much bending pressure will be on the spacer rods.  The author uses 1" diameter 3' solid fiberglass rods which are very strong and heavy .  I was thinking of using  1" or even 3/4" PVC plumbing plastic tubing instead. They are very lightweight and reasonably stiff at 1" diameter.  The mechanical  equation is 3' wide and 3' long for the center spacers. The end bridle appears longer.  If, say 100 pounds is pulled on the end rope, how does that translate into folding/collapsing the spacers?  Not sure if the center and end spacers see the same load or if 1" PVC is reasonable..

Or are 5/16" driveway solid fiberglass markers better for less wind footprint but has less bending resistance as a compromise?


T

I forgot about this online version of the fat dipole.
The numbers are the same, but the detail at the center shows important improvements that limit the crushing effect of the wire tension in the middle.
The second thing is that one can do the very same thing at the ends of the elements by supporting the ends with straight through ropes rather than angling the ends to a single support rope.
If you do this, there will be much less vertical thrust on the spacers if we keep the pulls parallel.

Also, in the original article, the rods are wood.
If you use the parallel pull instead of triangles, pvc might work, but 5/16 or 3/8 fiberglass rod will cause less wind loading.
Url for an article by k7mem with calculator:
https://k7mem.com/Ant_Fat_Dipole.html

Thanks for the additional info, Mike -

It's certainly getting heavier with the load of insulators in the center.  

I'm looking at your other approach of using "straight thru" double ropes.   How about these changes?....   The results would be no need for spacers, only one insulator in the middle (and one on each end leg) as well as a stronger structure by using  two rope supports on each side. Use a "bow tie" fan dipole config with 10' spacing on the support ends that would give an average of 5' spacing (or more) thruout the two dipoles.

It would mean another two tower climbs and two more ropes and pulleys.  But I think it would be a more manageable thang. No wind spinning either. Less ice loading.  I wonder if increasing the support rope  spacing at the ends to 20' would increase the bandwidth more?    The lower dipole could be near horizontal -   and for mechanical advantage the upper dipole could be sloped upwards by 20' higher at each end.  (like a truss that would actually help support the center - feedline, insulators, ferrite core weight and lower dipole)

Also, what if the two dipole legs were cut for 3790 and 3870?  This could produce a broader 1:1 "double dip" in swr between the desired  3700 - 3885 MHz band that is desired. (Assuming I can match the 75 ohm feedline to the dipoles well.)


Just thinking....

T

Tom,
If you stay with the wires being parallel, then you may want to have at least little insulators in the mid spans for stability, though, if the wire is tight, it is unlikely to twist together.

Your thought about separating the ends brings up another type of multi-wire antenna.
Guys that have run fan dipoles have discovered that adding a second-in band wire and spreading the ends gives a nice broadbanding effect. Twenty feet might be necessary to limit interactions and detuning the most effective versions have the second dipole going off to the side by 20 or more feet.
Usually, the first dipole is set at the low end of the desired range- maybe 3600khz and the second at 3900khz. The low one is put up and length worked out for that range and then the second is added and trimmed for best overall coverage.
Seems like the swr curves are similar to a critically coupled double tuned circuit with two small  dips at the end and a flat dome in the middle less than about 1.6 swr.
This is not fro, experience though, so in my case I thought to make it a couple of inverted vees, so the ends would be there to trim.
At 100+ feet and a nearly flat top, I think that you might just go with calculating the lengths closer together - like 3700 and 3900 and put it up and scan the antenna with a impedance meter and trim the bottom to pull it up.
For these things, there does not seem to be any reason to join the ends, by the way and they will act like a skeleton bow tie antenna.
Here is the article on one version. They successfully added a 40 meter dipole in the middle at no extra charge either…😉

https://wireless-girl.com/Projects/Antennas/Broadband80mDipole.html

If you were going to use the cage dipole idea, the dimensions are apparently somewhat critical in terms of impedance and also, the height.
If you spread it st the ends, it might look more like the fan version, even if you kept tue connection together. In my opinion, adding a dacron rope between the center insulator to each side 10 feet above the cage straight through terminations would add a great deal of strength and allow your copper wire to work well.


Even better idea, IMO:
Of course, a 3/8 dacron rope could be run between the cage elements, too and keep it more compact. That stuff can hold a ton easily, I think.

By keeping the ends compact, the ends could terminate in an aluminum tube or large fiberglass rod maybe 6 ft long so it is below the cage, with a single rope passing through a big pulley and a second check rope at the bottom of the tube or rod dropping straight down to prevent the end from twisting.
With this setup, you could lower and raise the entire array from the ground, if you are clear of guy wires, etc to the tower bottom at that angle.
You get a cage that can be raised and lowered and optimized from the ground.
Best solution, IMO and what I had decided to do on my shorter towers.
73, Mike

A string of beads isn't the best option.

I purchased 4 inch cores and wrapped coax through them


A lot lighter and a LOT more choking impedance.

--Shane
WP2ASS / ex KD6VXI

Agreed:

http://www.karinya.net/g3txq/chokes/

http://www.audiosystemsgroup.com/K9YC/K9YC-old.htm


The bead string will help a little but insufficient to be effective according to these researchers.
It is why I recommended 16 turns of rg400 through two 240-31FT cores. Will give about 12K choking at 80 meters…
Two single 12 turn windings in separate cores even more effective and easier to wrap

Ok on all, tnx!

Some more ideas...

Since the RG-11 is so light and I have plenty of it, I wonder how small  can coils be wound with it?   I have three large ferrite cores, about 3" in diameter. I could wind three large coils, two turns thru each big core, with the three placed in series hanging under the dipole center.  I was thinking that 14" coils might be big enuff to stop any coax migration. What you think?

I would have to mount the coils at right angles to each other to minimize coupling I think... That could be a challenge to mount.

Today I put up a 30' high mast under the dipoles to support the RG-11.  This will leave about 65' hanging down from the dipole and reduce the strain on the coax and the dipoles.

Also, I will be replacing the end ropes with 3/16" aircraft cable.  I think using a pulley with a heavy load just asks for the rope to fail.

I want to go with the fan dipole idea... with two or maybe even three dipoles that are staggered between 3.7 to 3.9 MHz frequencies.  It will be an experimental thing to find the best swr curve. Drop, adjust, raise, test over and over.

 I still like the overhead truss dipole idea.  I have some old Phillystran fiber guy rope that can take a few thousands pounds. Lighter than rope. I was thinking of using that it an overhead trussing arrangement, but not sure how to do it yet.

T

Tom,
Jim Brown K9YC published this in about 2008. He gives information for using big large coax in big loops like you describe.
He specifies 5-FT240-31 stacked for 80 meters. See article here:
They seem bulky and heavy to me…
http://www.w4ava.org/articles/k9yc-rfi.pdf

In his later work, he went to rg-400 teflon coax  or twisted insulated wire like teflon awg 10 aircraft wire and it made the chokes much lighter and more compact.
This was published in 2018.

http://k9yc.com/2018Cookbook.pdf

The smaller chokes can be enclosed in plastic Electrical boxes at the antenna center of the antenna at the feedpoint and the rg-11 feedline.
I had initially recommended rg400, but you may be better off using the paired teflon coated wire he discusses in the 2018 cookbook.
The impedance of the twisted wire is 80-90 ohms and he says it will be fine for the match of a high dipole. Check it out…
So many choices…😉

Edit: Just found some more data on rg11 catv cable. Loss at 1.pmhz is 0.22db/100ft.
Should be fine at HF low end.
Also, min bend radius loaded is 8 inches or 16 inch circles.
Unloaded is about 4.5 inches, but wrapping into a toroid is a loaded application I think, so you need to use big loops. Maybe two stacks and wind them like a binocular core?
This is going to be bigger and bulkier than paired Teflon awg10  or teflon coax in one core like k9yc used in 2018 cookbook…

FB on the RG-11 specs, Mike.   Good info that I printed out.  It appears to be acceptable for this use.


So it looks like it will take 260 pounds of pull. Is this what they mean by "loaded" at 8" bend radius?  (16" diameter at 260 pounds)   So if it is well supported, maybe the proposed vertical drop of 65' will not hurt it.    I always use a 15-20 turn "pipe hitch" rope knot, like a hangman's noose - like a Chinese finger grip, to distribute the coax weight pull more evenly.

The 300V rating at 75 ohms seems low to me considering RG-213 can take a few thousand volts.

Think I will try a hank of 16" diameter RG-11 turns thru my big ferrite cores at the dipoles' feedpoint and be done with it for now. That's less than one pound of extra coax weight. The ferrite is a couple of pounds, so not bad. Continuous run with just one connection at the dipole input. I can always improve on it later.

I wonder if we supported the RG-11 coil hank by itself with no pull on it at all, would a 4" bend radius be permitted under the "unloaded" category?  (8" coil diameter)


Tnx again for the great info!

If you’re worried about the loaded radius of the coax, you could use something like this to have a coil/choke with no load on the coil itself..

Ed

Tom,
The 16 inch loops sound fine to me.
You might tighten the loops to 12 diameter if you relieves stress completely so no pull was present in the turns except the pressure of the turn itself.

The 300volt spec is rms so you are talking 420-430 peak.
This stuff is low density foam so it cannot be compared to solid PE for dialectic strength.

425volts peak is equivalent to over 2kw at 75 ohms on a flat line.
I suspect that the voltage rating is conservative, Also and it will stand over 1000volts on peaks .
You could take a few feet - remove shield from each end for a few inches and run a hipot test on it to see how much it will stand.
By the way, foam dialectic rg8 is rated at 600volts rms.
Foams are for low lids, not high voltage. MB

FB Mike -


For end supports, I decided to go with 3/8" polyester rope and pulleys instead of the wire aircraft cable.  Same price.  Two ropes per side oughta make a solid structure and with 20' end spacing at 115' / 95'  it will allow a decent droop to lighten the load.  The bottom dipole will be flat-ish and the upper one will have an upward truss slope.

Still not sure about the balun fine details, but close..  I may mount some 10" diameter RG-11 turns loosely sitting around  a 4" diameter ~8 inch long ABS pipe and also use the pipe as the center insulator for the legs. I can also mount a few beads there too. Low weight is important to me.   It's a big project to get this up and working.

If I have, say, 10 turns of RG-11, where is the best spot to add the three large ferrite cores?  Should I put one on the input of the coil, thru the coil and the third one after the coil at the dipole input?  Or put all three on the coil - or all three at the dipole input? Any feel for this?

Yes, the RG-11 should take the power.  I ran it on 40M at full DXing power for years with no problems.  The thang that killed it was the water contamination I told you about. And even then, I didn't even see the signs of contamination until I replaced it and looked at the coax -  dark brown for its full length...  ;D

Ed:  I like your idea of attaching the coil with heavy duty heatshrink/glue.  That will keep it floating with the stress off it. I'm looking into that. Also looking into tying it on with rope lashing. I'm good at that from the Boy Scout days... :-)   I will keep the coil ends facing the dipole legs to minimize coupling.    The main feedline below will be supported by a rope pipe hitch as I described before.   Sounds like a plan!


T

The sunlight and shadows near sunset caused me to get out the camera.  

T


Pic #2 is a rare view of the delta loops wire. They are usually washed out by the sunlight. The sun is JUST at the boom - before disappearing.  BTW, that boom hangs on a pin and is guyed by the loops. No torque stress on the tower. It sways slightly in the wind. Just below the loops is a 40M reference dipole at 100'.

Pic#3: Just mowed the lawn yesterday.  

More:

Pic #1:  Yaz puts up with a lot around here, but gets plenty of exercise following me around.

Pic #2 shows the 40M stack. Top of the hill.  Gotta climb up there to finish the job soon.

Pic#3 is a rare telephoto shot of what it looks like at the top of the 190' tower. That is the 40',  4.5" boom holding up the two 75M delta loops.  I put that up in 2013 and still works after recent repairs. Worked a lot of Russians and Euros on 75M with that array.  I still remember leaning out there to attach the boom to the sidearm.  Scares me just looking at it.   

T

For the balun, I broke down and ordered (20) type 43 ferrite cores, just like the ones used on the class E rigs.  FB-43-1020.   No coils of RG-11.   Now I can keep it light with just one insulator in the middle and six ferrite cores slipped over the dipoles' feedpoint.  It will solve a lot of problems and worth a try.  

This is the classic W2DU choke balun version.   A friend suggested it and I read a bunch of old threads written by Walt W2DU and decided it was the best choice at this point.

Hopefully the simple 20' leg spacing and staggered frequencies of the two dipoles will do the same broadband job as the heavy, complicated cage dipole. The cage would never stay up in an ice storm here.... ;)   Now the center weight will be one ceramic insulator, about 65' of light RG-11 and six ferrite cores. Maybe a few pounds at most... and held up by two ropes per side with an overhead trussing effect.   I like it!  

T  

Pic#1: The garden is growing like crazy. We usually end up giving tons of tomatoes away.  

Pic #2:  My first tower, Rohn 45, 150' put up in 1986.  After repainting with zinc paste, it's still solid and could last another 40 years.  Star-guyed and uses three sets of anchors going out 30', 90' and 140'.   That tower has seen a lot of big antennas on it over the years. It's the only tower not holding up an antenna right now. Been thinking hard for something new...

Tom,
A 4.5 inch diameter 8 inch long coaxial coil will have about 18 turns and 15uH which has about 500 ohms of reactance at 80 meters.

I have included some charts showing chokes made with rg400 on FT-243-31 and FT400-31 toroids that have 8-12k ohms of choking impedance.
This method allows layouts that can be weatherized inside 4 inch sewer pipe caps.
Much better choking and light and compact.
See charts here and link to the cookbook below.

See page 14 for layout designs
http://k9yc.com/2018Cookbook.pdf

Your physical support system sounds fine from your description.
73, Mike

Tom,
I know you are leaning toward a choke balun that uses the rg11 straight through approach, so here is a lot of stuff that can help with that. IMO, Jim Brown has done more research than anyone and his presentation at tje bottom- and old one can be of great assistance to understand balun chokes.
73, Mike


https://k6jca.blogspot.com/2018/06/transmit-common-mode-chokes-11-current.html

https://www.google.com/search?q=ferrite+balun+choke&tbm=isch&ved=2ahUKEwif4bjJs_H4AhWYBc0KHVX1DvYQ2-cCegQIABAC&oq=ferrote+balun+choke&gs_lcp=ChJtb2JpbGUtZ3dzLXdpei1pbWcQARgAMgQIHhAKOgQIIxAnOgYIABAeEAg6BwgjELACECc6CAgAEB4QCBANULQYWK4tYPFjaABwAHgAgAHWAYgBlwmSAQUxLjcuMZgBAKABAcABAQ&sclient=mobile-gws-wiz-img&ei=fmPMYp-qM5iLtAbV6ruwDw&bih=897&biw=1366&prmd=svin&rlz=1C9BKJA_enUS931US931&hl=en-US#imgrc=N16WCM8NxUCqGM

https://www.nonstopsystems.com/radio/frank_radio_baluns.htm

https://www.nonstopsystems.com/radio/frank_radio_baluns.htm#chokes

http://www.audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf

http://audiosystemsgroup.com/CoaxChokesPPT.pdf

Image of a big coax wound choke using a stack of toroids

Since the choking impedance goes up with the square of the turns, a string of beads today is foolish.

I have seen well over 8kohms of choke on an optimized choke balun made of LMR240.  Typically you can get over 5k on a hf choke.

How many beads is it going to take to get 5k?  A LOT!  Like over 50, IIRC

--Shane
WP2ASS / ex KD6VXI

Lots of info, thanks, Mike!   I read thru most of it.  There certainly are a lot of different opinions and approaches.

I think the main thing in this application is that I need something lightweight due to no support at  the center - and a minimum impedance that will still work.

I understand that  a minimum X5 of the input impedance will  still do the job for the majority of unwanted current. Maybe -20 dB isolation?  So at 75 ohms X  5 = 375 ohms.  I can eek out this impedance with a string of beads based on info I've read.  If I start to see  it get squirrelly, I can always add some coil turns or more beads.  But for now I want to keep the package small to see how it flies.  

Each FB-43-1020 bead = 1.75 uH.     9 beads slipped over RG-11 =  15.75 uH.      At 3.800 Mhz =  376 ohms inductive reactance.   75 ohms X 5 = 375 ohms.  Right at the hairy edge....  assuming X5 is an acceptable margin.

I should have it working within a week when parts arrive and will report back.

Thanks again and I appreciate all the extra effort, OM!!

T

Ok, Tom. Good luck.
One thing you should note from Jim Brown’s and others’ presentations is that choke baluns work best when they use materials that have as high loss resistance as possible. I believe that W2DU used type 73 material that had very high mu and high R value and later work with toroids utilized the high R value of Type 31 material.
The secondary consequence of harnessing loss impedance is that any residual current will result in heating of the bead or toroid.
We all use very high values of resistance as voltage dropping resistors because it also limits current, say- for driving the screen of a tetrode. In tjose cases, we want residual voltage, so calculate how big the resistor needs to be to handle the power  and still provide the voltage needed.
In this case, we want zero volts-ideally below our “dropping resistor” (choke), so the higher the total impedance the better and the higher the R part of the impedance, the better it covers a wider range of frequencies  without becoming capacitive.(above self resonance).
That is why Jim Brown and others recommend as high an impedance as possible because the current is body slammed to nothing, even when high power is involved.
If the impedance and R value are lower, then any significant current can cause the beads or toroids to get very hot and self destruct.
The 500 ohm rule makes sense when talking about lossless inductive reactance, but if you are talking about a lossy balun, which these things are in the common mode, then any current will inevitably cause it to heat up.
The thing that mitigates this for bead strings is that they get a lot of surface area, so they can dissipate heat easily, compared to a toroid in an enclosure.
My preference is the enclosed toroid, but making the toroid have 16-18 tirns and having 12-16k of choking impedance, so currents are effectively reduced to nearly zero. They are also pretty compact and light when made with rg400 or paired awg10 teflon wire.

Still- the experiment may work for you if you have the #73 beads that W2DU recommends.
73, Mike


https://owenduffy.net/balun/W2DU/index.htm


Edit: just checked and W2DU used #73 beads that can accomodate 0.195 diameter coax, but they do not make the big beads in 73 material.
If you use #31 beads, the mu is 1500 vs 5000 for 73 ferrite, so the choking impedance is lower. Tough choices here…MB

Mike,

After doing some thinking, another thing that comes to mind is the real world applications...  

I think the common mode isolation requirements of a simple dipole with the feedline at perfect right angles is less stringent than say, a stacked, phased driven Yagi array.   The difference in a 375 ohm balun performance could be -20 dB  vs: -25 to -30 dB for a 1000 ohm - but still perform acceptably.    The radiation patterns may be the difference between lazy, broad lobes to very sharp, -40dB nulls.

For a "local" higher angle  dipole application, I think the broader lobes (if present) might even reduce communication fading by filling in the sharp nulls. Especially the moderately sharper pattern of a 75M dipole at 100'.  Whereas for a phased, driven array, we like to get all the sharp nulls and performance we can, thus baluns that are 1500 ohms or even more.  On my 40M triple Yagi stack, I used 14 turns of RG-213 on a 4" ABS form and 8 ferrite beads at each Yagi feedpoint.  The f-b and high angle suppression can approach -30dB or higher at times. I know it works well.  They are supported at the feedpoint by the boom, so no structural issues there.

But I think the broadband dipoles planned will do fine as a local and refence dipole with -20 dB isolation AND as a benefit being physically light at the feedpoint to survive the storms..

As for local noise suppression, I pay close attention to this. The noise level on 75M during the day is below S1... really nothing there to suppress. Neighbors far away -  antennas and power lines far away.  At night noise will propagate in based on storms across the country.   So this is my rationalization to getting away with a more marginal beads-only balun for the broadband dipole.  

BTW, the 75M loops use an openwire antenna matcher -  and uses ferrite beads  into the  50 ohm link, so is well covered there for common mode problems. That is a performing antenna system that needs good isolation for pattern sharpness and DX hearing..

The thing that does concern me is about the possibility of wasted or damaging heat generated by the beads.  I will test this with a 1500W  carrier for 5 minutes and then quickly drop the dipoles down to do a touchy-feely...  ;D   The beads will be supported below the feedpoint in open air for cooling with their weight transferred to the center insulator..

T

Tom,
I had not considered specific criteria for this individual application.
If local (less than 500 miles is going to be most of your working area, there is good reason to think that a radiating feedline could be a good thing, given the fact that you are up 3/8 wavelength with a flat top dipole.
If local rfi is not a comcern, one might forego the balun at the feed point completely
and insert a very good choke at 1/2 wavelength from the feed point where it is a voltage minimum on any common mode currents.

I need to confess that I am a fruitcake for over designing everything… Old habits!😬🤪😁

I,doubt that the beads will get very hot, because it will be only a few watts and it is open air.
Hey test it at night and if it looks like a sparkler- try something else…😉😂😂
Let me know your results. 73, MB

Mike,

You said:

"If local rfi is not a concern, one might forego the balun at the feed point completely
and insert a very good choke at 1/2 wavelength from the feed point where it is a voltage minimum on any common mode currents."


Could you elaborate on this technique, reasoning and benefits of doing this?  Why not do it all the time instead of at the feedpoint to reduce weight and easy accessibility?  I read about it but not sure I understand what is going on there...

T

Full disclosure- I have not personally tried it.
The theory is that if you do not put a choke at the feedpoint or a balun, there will be common mode current flowing on the shield of the coax.
Normally, we do not want common mode current because it can result in RF getting into the shack, and also causing RFI on the feedline pathway.
Also, the shield will change the impedance of the antenna because it will effectivel look like a finite parallel load.
It will also make the directional antennas likely to have extra spurious lobes and interact with the beam pattern.

In this specific case, a secondary vertically polarized radiator can actually benefit local communications for short hops and ground wave, if the current is significant.

Still- the presence of rf in the shack and burned lips from touching a hot mic is not attractive, so we still need to eliminate rf currents at or near the tower bottom.
Since the common mode current will- like the antenna have current loops and nodes and alternate voltage variations, the placement of the choke on the ground can be more effective if it occurs 1/2 wavelength or a multiple of that from the feedline and we are talking about the shield, so it will not involve velocity factor in locating that point. For 80 meters, it will be 130 feet from the feedpoint therefore, I believe.
Maybe someone has actually implemented this and can correct or confirm these ideas?
It might be worth trying…
I put a good choke at the feedpoint of my Tennadyne T8 and another 66 feet below it- likely overkill…😉 MB

Edit:I have toyed with doing this very thing on a flatop for 80 meters, but my height is only 65 feet, so I would need to extend the feedline another 1/4 wavelength, so it would not be as good as your 95ft height where you just need 35 feet more before the good choke.
Besides-mat 65 feet, my antenna is already high angle radiator..

UPDATE  7-16-2022:

Mike and those interested in some results for the fan broadband dipoles project:

I'm very pleased with the initial results! Over the last week all the parts came in... 500' of RG-11 75 ohm coax, weatherproofing supplies, rope, etc.   I got some nice Polyester 3/8" braided rope. Beautiful stuff for the pulleys. Now that everything is up on the tower, I can work from the ground.

As planned, I made up some homebrew RG-11 connectors as well as weatherproofed everything. I made the center very light with nine ferrite cores and just two insulators. I supported the RG-11 at 30' high off the ground. The dipole centers are at about 85' because they are loose and sag by design.  The double ends are at about  105' and 85'.  I think this is the optimum height for local/moderate distance on 75M.

Today I raised it all up and finished the connectors and ran the feedline.  I plugged the MFJ-259B in and nervously anticipated the results.   The 75 ohms J0 point was about 5% lower. (as predicted by the articles)  The system resonated at about 3650.  I want it at about 3825.  This is about 6 feet too long.  I can fix that tomorrow and trim it to bring it up to 3825.  The great part is that the swr stayed below 2:1 from about 3.4 Mhz all the way up to 3.9 MHz!  So once I get it trimmed up to 3825, it should do 3700 to 3900 easily with 1.3:1 or less based on my brief tests today.

Bottom line is the 1:1 swr dip is very smooth and broad. It's like a dummyload within the first +- 100 KHz.    I really should have made an antenna like this long ago.  Every ham needs one accurate antenna... ;D   I see no signs of antenna interactions / or feedline radiation.  I'll have some accurate measured curves soon.

So I will be keeping the legs both the same length. The swr curve is so clean and flat that I don't want to mess it up with staggered "W" double dips and that stuff. The 20' leg spacing with equal legs is very FB as-is. My other single wire dipole at 90' had a very poor, sharp swr curve in comparison.  I think this may be better than a heavy cage dipole certainly for  weight - and performance.

It's hard to see from the pics, but I put a lot of time and effort into the center insulator area.  The RG-11 is supported by a long rope pipe hitch, like a hangman's noose, a Chinese finger grip knot.  The weight is well distributed.  Also the 9 ferrite beads are supported by the center insulator to keep the weight off the RG-11.  I have the RG-11 supported on a mast so that only 65' is pulling down.  The RG-11U is happy and really VERY lightweight.  Small wind profile overall.

I made up copper sleeves as the RG-11 shield connector.  I then used three different waterproofing techniques using 3M tape, rubber tape and liquid tape.  Best made wire antenna I have.  The stress on the ropes and pulleys is surprisingly light considering no center support.. I expected a very hard pull, but as you can see from the pictures, the dipoles are just loafing along. I think it will do fine in wind and ice storms.  There are no trees swaying since all is anchored to towers.

Listening on the air with A/B tests, there is a tremendous difference between the high DX delta loops and fan dipoles. The locals are weak on the delta loops and strong on the broadbanded fan dipoles, sometimes by as much as 20 dB difference. This tells me I have the heights dialed in pretty well.

There will be more testing once I bring the system up to the 3825 area.   The swr should be reasonably flat around 1.2 : 1 on both 3885 and 3775 exceeding my two goals.

Thanks again for the suggestions on this project. It appears to be the best of a few worlds;  light weight, broadbanded, durability, efficiency...the design that is.

T
 
Pic #3 shows the 30' high "relay" support of the RG-11

Pic #1:  Notice the lazy droop on the dipole legs.  Very little stress. It could be pulled much higher, but it will last longer loose. If I wanted it higher, I'd climb higher...  ;D

Pic#2:  Ferrite support, RG-11 support, #10 antenna wire, rope pipe hitches and weatherproofing all in one lightweight, low wind profile package

Pic #3:  The 75 ohm aluminum hardline uses my standard homemade connectors. Uses 3/4" to 1/2" copper plumbing adapter, SO-239 and an inner pin from Andrew Co.  The RG-11 uses a copper sleeve and SS hose clamps to connect to its aluminum braid and foil.  It should handle a KW no problem.

More:

Tom,
That is a beautiful, compact lightweight mechanical design and the performance you
Got on the first cut was excellent and compatible with the results the W4RZL published in his August 1968 QST article. Page 47,48.

In that article, W4RZL added a 40 meter dipole and a 20 meter dipole with good results. If I did one, may just do the 40 meter pair addition.
 This design is very good mechanical design too, because it forms triangles for great stability and the sag from the top gives much more support without over stressing the wire.

W4RZL did stagger the lengths, but if you are getting good results when they are the same, fine by me. I do wonder if a lesser difference, but not the same might be wider and give a flat middle, rather than the W you mention.
Since you have to cut it down anyway, why not cut down the bottom and leave the top tue same and see what happens.  What do you have to lose and you might find that it is flat all the way to 3990 and down to 3650…
If it does give you a “W” you do not like, slowly trim a bit off the longer (top) member and record the pattern. I bet you will find a length that gives you a flat plot in the middle and even more width.
Another thing is the 43 material is not as good as the 31 material for 80 meters. The analysis article showed that the 43 bead stack peaked much higher above 10mHz and tje 31 beads were pretty good at 80 meters. More 31 beads is better, IMO- not 43 beads for 80 meters…Much higher choking impedance.
Also, the 43 bead setup will change the load impedance at 80 meters. Not a good idea to change more than one variable at a time…🤪
I will look up the article on the W2DU designs and post it again.
Great progress, Tom, but stay with it amd you will find perfection in the next iteration or the next.
73, Mike


Edit: Here is research in W2DU Bead baluns.
Note where the 43 material peaks- much higher than 80 meters.
31 still not as good as 73 beads, but better at low frequency than 43 beads.

https://owenduffy.net/balun/W2DU/index.htm

Hi Mike -

That's a good idea to trim some off the bottom legs only as an experiment.  Nothing to lose to try. My guess is it will help widen out the curve, but we will have to see.  I'll give it a try tomorrow and see if it widens out.  

Yes, I am using nine 43 material ferrites. These are the same ones used in the class E rigs on 160 and 80M.  I should end up with at least 500 ohms on 75M, so it may not be as high as using 31 material but should be enuff to do the job.   The only way I'd tear down that center insulator now is if it burned up.... ;D

Once I post some final curves, I'd like to see some other guys post their curves using whatever they have.  I'm wondering how much effect height above ground or other factors affect the swr curves.


BTW, here's a pic of the towers from about 3/4 mile away.   We are NE of the towers, towards Eu, my favorite direction.   Another simulation glitch: There are supposed to be four towers there. For some reason the 120'er is supposed to be on the left, but is not there. That is quite the mystery to me.   More proof the alien computer can't keep up...  ;)   The tower on the left is the 190'er holding the delta loops. The one on the right holds the 40M 3-stack.    The missing tower (on extreme left) is supposed to be holding one end of the fan dipoles.


T

Hi Tom,
Hey- I told you Imwas a fruitcake for details. If the beads do not explode, they will do a great job and if you have residual rF on the line, as I said, just add another choke 1/2 wave down the line (125-130 feet) and it wil scrub it up completely.
I am anxious to see the results of your trimming the bottom. I feel confident that you will see less than 1.6 swr out to 4.0mhz and less than 1.5 from 3650 to 3950 or better.
Yes- height (and length😉) matters!
73, MB

OK, will do.  Tnx Mike.

Today I'll lower the dipoles to trim the legs and also measure the coax from the feedpoint and find the 125' point.  This will be easily accessible to add some ferrite cores. I left some extra RG-11 coax in the run that I could even add some turns thru the ferrites.   That will put the balun question to bed.  

I'll also play around with the leg trimming and see what happens.

It's a circus to lower all the legs and feedline and avoid twisting and snagging on stuff.  I'd like to get it finished and add the last bit of waterproofing.  Still need to climb and finish the 40M stack feedline weatherproofing.   There hasn't been any rain for a while.... good for the work - bad for the lawn.

BTW, you said, "if you have residual RF on the line"   ----      what is the best test to determine if this is an issue?


T

Tom...  If there is RF on the outside of the line, it should show some periodicity.  If you have something to read line current...on the order of a pickup loop, a diode and a sensitive (50 uA) meter,... you can run it along the line and see if there are peaks and nulls.  Of course this exercise in nontrivial if the coax is high in the air.  But you don't have to run the whole line, just a quarter wave section of it, perhaps even less to see a trend or the absence thereof.   I think the famous MFJ may have sold a clamp on current meter that you could use, as long as there were no QC problems in it.  Mix 31 is the stuff to use to cool things off at the wavelength of interest.
73 de Norm W1ITT

FB Norm -

Your test technique makes sense. I should build one and do the test on all the antennas here while we're at it.

Mike you were very close with your swr predictions.  I carefully pruned the legs and tested the fan dipole at least 10 times looking for the best general swr curve.   I went too far and then stepped back to find a compromise that JUST  covers 3.5 to 4.0 MHz at less than  1.4 : 1  swr.    I ended up with two staggered 1:1 swr dips -  one at about 3775 and the other at 3870.   The curve is not as perfect as the first one I got yesterday, but it is broader and covers the whole band - and the dips are close to my favorite operating freqs. What's not to like?  If I get down to the AM operating areas like 3625 - 3750, etc., the swr is really quite good.  The DX window at 3790 is 1:1.   I cannot recall ever having a 75/80 antenna quite this good that was coax fed. Openwire and a matcher was the only way except for one of those load resistor antenna hack jobs.

I didn't add any new ferrites yet to the 125' voltage point as Mike suggested, but will figure something out now that I located the proper spot on the RG-11 feedline.

All in all, I would highly recommend this fan design.

It should start at about 5% shorter than the 468/f formula.  It will need to be pruned and tested after that.  Much will depend on the leg spacing and height above ground, as well as straightness and flatness.  This project took a lot of time and effort - more than I expected....

T

Tom,
I love the results you got and your patience in trimming paid off.
That might theoretically be termed a “W” curve, but when that middle hump is as wide and flat as I imagine it is, we can call this thing FLAT! 😉😎
Of course, your results will only be replicable if the heights are the same for the copy, but that just means a bit different length. Starting low and trimming makes a custom design easy, if a bit time consumimg.

Your idea that the lengths be shortened by 468/f -5% is very similar to the ABRA fan dipole recommendation of 468/f x 0.96
See formula here:
https://wireless-girl.com/Projects/Antennas/Broadband80mDipole.html

The fact that you have independently seen optimal results by this identical formula makes the process much more likely to be successfully copied when trimming for height and other factors are added in.
Excellent work! 😎

Now, back to suppression beads:
I have copied links to the same beads in 43 and 31 material and the images for tue curves on both and fir this suppression application, the 31 bead is clearly superior.
I know that you have a lot of packaging and time in the stack on top, but if you want a stack of beads at the 1/2 wave voltage minima for any residual common mode current, the 31 beads are best. Actually, however, a number of loops through 5- ft240-31 cores will be much better than that, giving several thousand ohms of impedance.
To answer your question about tracing down currents- like brushing and flossing daily, one need not get rotten teeth and gum disease to use preventive care..😉😂.
If you do wish to look, however- odd 1/4 wave points are obvious places to sensing field meter.
If you have any SDR equipment, the acceptable level of rf in the shack is so,ething less than zero. By the way, so keeping the devils from riding common mode paths on feedlines, rotor cables, etc is essential. Like gum disease, if you never get it, it might be doubtful if you ever would have without dental hygiene, but who wants to run that experiment either? 😱😉😂
How about publishing pics of your curves?  Outstanding results should be shown.
73, Mike
Edit: Note in the curves the Rs values. The Rs value is very important in wide band suppression and is related to loss impedance. Ot can never go capacitive like regular Inductive reactance and tjis gives much better suppression of common mode currents. MB
43 bead:
https://www.fair-rite.com/product_datasheet/PN2643102402.html

31 bead
https://www.fair-rite.com/product_datasheet/PN2631102002.html_

If you have residual rf on the line past your common mode choke you need to find out if it's be ause it's being picked uo by the proximity of the antenna (usually because you aren't at a 90 degree angle from the feed point) or because your choke is letting it by.

If the choke is letting it by you can find problems like cracked ferrite, permeability change, etc.

This is why I got for 5k or better impedance on my chokes.  If you don't design for it, a string of beads can eventually fail at QRO.

W2DU and I had this conversation when I showed him my string of beads.  He warned me that any residual common mode could cause issues down the road.  I used a MFJ  current analyzer for open wire line to make sure my common mode was down to nill.


Also, and probably not a problem due to the remoteness of Tom's qth, but will be of interest to city dwellers, having a common mode choke removed from the feed point (as the first choke in the system) is a nono.  The reason is thus:  if you ha e noise being picked up by the shield.


The coaxial cable is actually 3 pieces of wire.  The center conductor, the inside of the shield and the outside of the shield.

Having your choke at the feed point will keep any noise ingress from among it at the outside of the coax shield from among it to the inside of the shield, where there is nothing we can do about it.

I run 2 chokes.  One at the feed point of the antenna and one at the point where the coax comes in the shack.

This keeps any noise shield currents from making it to the inside of the coax at the feed point and also keeps them from being carried in on the shield into the shack.


I know you run 'legal limit' am, Tom.  Keep in mind that you can have a substantial rf current on the outside of the coax.  Is it enough with a string of beads?  K9YC says it will take appx 50 beads to make sure your common mode choke doesn't experience issues.  Maybe he's wrong.

--Shane
WP2ASS / ex KD6VXI

Jim Brown has earned his knowledge by thousands of hours of work and research, do the chance he is wrong is near zero, IMO.
I have studied his work and it is very extensive and scientific in his careful metrology.
All you say is true Shane, but even 50
Beads will not come close to a single FT240-31 wrapped with 13 turns if rg400 or better yet - two 12 wrap FT240-31 in series which
Jim’s data gives over 12k of choking impedance.
Tom wants to light those
Post 4th of July sparklers up there, though, I think, do I am supporting his determination to
Prove it one way or the other.😉😂😂😂

OK on the 50 beads. Got it covered.   Almost all of my antennas are supported in the center, so I have coax turns on ABS plastic forms - with ferrite cores as mentioned.  The only antenna I have not supported in the middle is this broadband fan dipole, thus the cores.  But as I mentioned, I plan to add an additional choke at the 125' 1/2 wave point.  I left about 25' of extra RG-11 in the run, so can easily add the choke to the system.  The turns will have to be large diameter as per specs, but I plan to wind a robust choke with cores before running any KW power levels.


How about I order one of these and wind as many turns thru it as I have room and coax?  One FT240-31 will do it at the 1/2 wave point?

https://www.amazon.com/Fair-Rite-Toroid-Core-FT240-31-Ferrite/dp/B01959LAFA


Question:  I have one of these Motorola field strength meters with a little antenna. How would I use a probe (clip lead) to sample some RF from the outer shield and make it a meaningful measurement?   I could put 20 watts thru the antenna and wind a few insulated turns around the shield... do as Norm described above?   This is one of those diode detector FS units.

T

I was kidding you a bit, Tom, but I was serious that your beads choke might work well enough.
Your idea about winding through several FT240-31 cores will provide a high impedance and locating it at a high current- low voltage point in any common mode currents should work great as long as you pay attention to the 8 inch radius spec for the rg11.

One possible difficulty not mentioned before I’d that the mu of a lot of Ferrite cores can reverse and drop sharply at a critical temperature.,
Fair-Rite publishes temperature curves to look at this.
If the choke has several thousand ohms of impedance, it will never get hot enough to matter, but I have heard of cases when bead chokes can experience thermal runaway and chronic overheating can degrade them as well.
It would be great if there was a thermometer that had a radio link.
I wonder if a wireless thermometer might work for that?
I have an indoor/outdoor thermometer with a 4xx MHz link to the jndide thermometer.
Not sure how much range it has though…
If it worked, the remote sensor could be taped to the bead bundle and temperature monitored to see if the temperature rises..,
Or you could pour the double 4-1000a amp in and see if it lights up or sparkles.
You have uniquely useful power to do the research…😉


It is possible that none if this gloom snd doom will materialize, however…

Tom..  That Micronta meter has most of the parts you'll need for a current probe except the pickup.  Get a ferrite split core in the plastic clamshell thing that allows you to clip it over a wire.  The hole will need to be big enough to pass the coax csble and a few turns of small wire.  On the stationary half of it, wind a few turns of smallish insulated wire.  The wire gets terminated with a resistor...maybe 68 ohms or so, then fed to a sensitive diode detector, then to a potentiometer, then to the meter.  Glue the stationary half of the split core to the top of the meter and it'll look similar to the ones that MFJ sells.  On his site, he offers two of them.  The "compact" ladies' parlor model even includes a schematic link in the description.  You'll have the only one with the esteemed Micronta name on it  after you do the modification.  Or you can spend more money and buy the "calibrated" unit and measure amps, assuming it'll pass the diameter of your coax.  Probably just knowing if there is a relatively large peak to null ratio is good enough for our purposes.
73 de Norm W1ITT

Using a clamp on with a secondary winding is a great idea.
I am attaching a screen shot from KF7P site.
I would get the #61 material for this purpose. They are ideal for flux transfer.
They are over 1/2 inch so there is room for some wraps and still close and slide easily.

Well, this is an interesting thread.

Having used ferrites in antennas years ago for baluns and 4:1 ferrite 10KW transformers with KLM's  dual driven element antennas, I found out that this isn't  good idea. 

If you exceed the peak flux density the ferrite is capable of, the ferrite becomes very lossy and will heat up under normal operating design conditions thereafter.

Well, what would do this. LIGHTNING!  A nearby strike and definitely a direct hit will slam the ferrite and render it useless.

I've got useless ferrites in my museum of crapped out parts slammed by nearby lightning strikes from years ago.  Took me a few years to figure it out.  Plus an engineer from  FaiRite to verify this happens all the time! 

Bottom line, DO not use ferrites on any antennas.

A solenoid coaxial choke optimized for a parallel resonance on the band is the best way to go.  You can get 10K ohms and better this way for choke impedance.

-Chuck

Hola Chuck -

Thanks for the input.    Yes, I remember the warnings about lightning and ferrites over the years but it seems to be disregarded by the majority these days.  But it does concern me cuz bad ferrite means major antenna tower work to replace it.

I've finished the 75M  broadband fan dipole project (for now) and very happy with the results.  I'm now focusing on the two delta loops for 75M.  Maybe you can advise me on that.  I plan to remove the openwire feed system and feed them both with RG-11  and some kind of balun at the feedpoints. They will be a forced fed coaxial feedline array, standard ~ 0 > 90 degrees phased, unidirectional with 40' boom spacing at 190' apex height.

So for the baluns you're recommending, I would wind, say, 20 turns of RG-11 onto an 8" ABS plastic pipe, just like a big coil and then resonate it for 75M to bring the impedance up to a high level, like 10K?  IE, no ferrite material at all...

Please describe this a little more and how the parallel resonance is achieved and measured...


T

This is a branch in the thread of this discussion and I must admit to being a bit confused and muddled by it.

The term “Balun” is in itself confusing, because we call several kinds of different items “baluns”.

Also:
I have to say, I have never thought of this aspect of lightning damage.
Interestingly, there is some literature on using Ferrite to suppress EMPs from static sparks to lightning strikes.
Check out the links below:


https://www.tvtechnology.com/opinions/power-surges-part-two

http://support.nautel.com/tips-n-tricks/shields-up/

https://disasterpreparer.com/product/emp-ferrites/


I googled antenna choke balun destruction by lightning and did not get any hits on Google.
That might not mean anything, however, if what Chuck says happens and the ferrites  may not appear to be physically damaged.
Just like human conditions lkke heart disease or cancer, changes can occur and we are-at least at first- unaware of,them.

 I would love more details on the part about increasing loss in the ferrite.
The only article I found was in the bottom link and that article says that even repeated heating of Ferrites above the Curie temperature had no long term effects and permeabilitu returned to normal  when temperatures returned to normal.
By the way, the Curie temperature is the place on the ferrite temperature curve where permeability falls off a a cliff

But back to the kind of balun we have been discussing in this thread- the common mode choke.
The entire purpose of a common mode choke is to stop any common mode currents from flowing on a transmission line.

Actually, the thing that males #31 material effective is the high Rs (loss reactance) in addition to the high inductive reactance it gives when a conductor,passes,through a toroid or bead. There is XL and Rs in any choke wound on suppression material like #31 and the higher the Rs, the more effective the choke will be.

There is a lot of literature on transmission line baluns and I believe that the whole point of these devices is to convert a differential signal in a coaxial cable to a balanced output.
I am not sure that a transmission balun is at all effective in suppressing common mode currents on the shield of the coaxial cable, however. I will research that question…

I can see how a transformer balun made from #61 ferrite or #2 powdered iron might lose that crucial low loss characteristic that makes is a great flux transfer medium, but a choke balun is at it’s best when it has the highest possible u” or loss reactance because a high loss material with a high inductance makes the best common mode choke balun.

My confusion, therefore is that I am not sure what Chuck means by the term “balun” in the context of his post

Maybe you can give more details on whatkind of baluns you have used, Chuck.

On to the coiled coax shunted byma capacitor and tuned to 80 meters:

I can see an  peril in forming a parallel tuned tank circuit from the coiled feedline to maximize the impedance.

The most obvious point is that the tuned circuit is inductive below the resonant point, but above that point, it becomes capacitive and the higher you look, the becomes first less useful and then useless and finally it actually encourages more common mode current on the shield.

Secondly, the Q of this Tank circuit that is formed. Obviously, the lower the Q, the wider the band where it will exhibit suppression of the common mode current.

It actually makes me wonder- if you were going to introduce a resonant circuit, you would not just use a quarter wave folded stub like we used back in the 60s before we had any cores to think about.
They exhibit a very high impedance to common mode current on the shield for some hundreds of KHz, I think.

I want to know more, but I am skeptical that this coil of coax parallel tuned is  better than the effective #31 choke baluns or the alternative folded 1/4 wave tuned stub which has been around a long time and seems to have a fairly wide response.

Please discuss. 73, Mike

Article on ferrites and powdered iron cores at high temperature. See pages 5-6

https://elnamagnetics.com/wp-content/uploads/library/Magnetics-Documents/Using_Magnetic_Cores_at_High_Temperatures.pdf


https://hamwaves.com/chokes/en/index.html

http://www.na0tc.org/lib/exe/fetch.php?media=technical:balun_p2_website.pdf

https://www.w8ji.com/common_mode_current.htm


https://www.qsl.net/wa3mej/Articles/Common%20Mode%20Choies/common%20mode%20chokes.pdf
Why reactive chokes are not a good idea- read page 2

Here is more data and information that was published by G3TFQ.
I consider his work and the work of Jim Brown to be the best out thereon common mode choke design.

Note the graphs in the attached picture.
The thing to look for is bands that are green with a black line through them.
Red means that the choking impedance is too low to be effective.
Green means that the choking impedance is greater than 4k ohms for olive green and over 8k ohms for dark green.
The black tracer indicates that the impedance is primarily resistive- not reactive.
Those coiled up pieces of coax with air dialectric are useless at all frequencies below 7 mhz and they are reactive at all frequencies which limits their useful frequency range, so they will become capacitive above their self resonant frequency.

https://www.qsl.net/wa3mej/Articles/Common%20Mode%20Choies/common%20mode%20chokes.pdf

If one does choose to use ferrites in a common mode choke, and K!KW gives us reasons to rethink that, it is well to remember that ferrites are not closely specified as to their characteristics.  One man's Mix 31 may not be quite what the next fellow's is and, perhaps, may not always be the same from batch to batch.
Add to this the fact that there are a things coming out of Commie China that are indeed ferrite but of varying quality.
If one decides to make a choke from a cookbook design it's probably best to choose a design that shows a wide area of good performance over your frequencies of interest.  And of course there's no substitute for proper two port measurements.  As long as the system impedance is near 50 or 75 ohms, one of the little Chicom fifty dollar network analyzers  of the NanoVNA series will provide useful measurements.
73 de Norm W1ITT 

I agree that ferrites are variable on characteristics and I asked Jim Brown about that in an email and Jim said that he  was aware of the variability, but that his cookbook allowed for that variability and if you follow it, you will achieve good results. Note! : it is best to read and study his papers before bothering him, because he has no patience for stupid questions he has already answered.)

Jim Browns results and recommendations have been echoed by G3TXQ, one of  whose articles I just posted a link for.

Given the variability, there is no evidence that a coil of coax produces sufficient choking impedance at 160 or 80 meters to be effective in eliminating common mode currents on coaxial cable lines.
Also, one of the major weaknesses is that they are reactive and therefore inductive up to self resonance and  capacitive above and when capacitive, it has been demonstrated that the problem of common mode current on the shield of the feedline.
The idea of shunting a capacitor across the coil of coax will provied a large impedance peak, but it becomes much less useful below and capacitive above resonance, so it seems like a doubtful improvement.

As for Chuck, I have the very greatest respect for his opinions and knowledge and have profited from his posts from the past. The fact that I took the time to ask questions about his assertions is in itself a token of respect and I am open to any scientific evidence that it is the best solution to this particular problem.
I do not consider myself an expert in this area, but I have read a lot of articles and found that Jim Brown has done some serious work that is solid and his conclusions and advice deserve to be heard and followed unless someone does anything close to his work and concludes otherwise. G3TXQ, W1HIS, Joe Risert and others have also made great contributions and I have great respect for them
If we begin discussing current baluns using transmission lines, my Jerry Sevick books get a lot of attention for the very same reason.

By the way, I was not aware that,Fair-Rite had their cores made in China, though it is not surprising and is certainly something that adds to my overall concern about our exporting expertise to their oppressive Communist government, but the relative merits of high Rs Ferrite chokes vs inductive chokes to suppress common mode currents on coaxial cable feedlines is a matter of empirical  scientific evidence, not political conviction.

Great discussion!  I'm learning a lot from your reports, Mike.    But my head is spinning as to how to proceed.   ;D

Let me state a few real world assumptions to see where we can go from here...


1)  Not all antennas have serious common mode problems. When using perpendicular feedline runs and simply "lucking out" with the layout,  the antenna may perform acceptably with no balun at all.  So it becomes a matter of degree - how much of a common mode problem does the antenna have in the first place?


2)  What is considered a high enough impedance for a balun?   For a 50 ohm antenna, is X5  (250 ohms)  enough or is X10 (500 ohms)  required to bring the particular antenna down to an "acceptable" level?   Is -20 dB enough or is -30dB?   This all depends on how bad the case of common mode is in the first place.

3) When using the thinner coaxes to wind multiple turns on a large toroid, (say smaller than RG-213) will the thin coax stand up to extreme QRO?   (power like a corntester might run)

4)  If a long string of ferrite beads is slid over the coax and actually does the job, can a simple test, like a 1500 watt carrier every month or so show any lightning damage by watching the swr rise from a baseline measurement when first installed?  IE, I'm thinking that because the ferrite bead technique is so easy and effective, a simple strap test every so often to verify the beads are still OK is not a big price to pay.  After a big strike they may need replacing - just accept it and make it easily accessible if possible.  My fan dipole uses cores and is easily accessed by ropes and pulleys, so no problem there.

5) Is there a false negative test for ferrites?  IE, if they explode into tiny bits, the swr may not show a rise, but the ferrite is ineffective.  Is there some other damage mode that does not show up with swr?

6)  If the feedpoint balun is of small impedance, would an additional  "token" balun, like 15 air turns and a few in/out ferrite beads on the ground, at the 1/2 wavelength point be a good insurance to further snuff any residual problems?  The ferrites could be checked by the periodic power strap/swr test also.

I'm trying to finish up my 75M delta loops new coaxial feedline project and obviously want to continue using ferrite -  but with some conditions related to lightning and minimum impedance required to do the job on 75M..


T

Tom...
In answer to your question (2), both the VOA and the Beeb want to see balanced-to-unbalanced  (common mode) currents on the balanced lines that go back to the transmitter hall at better than 26 db down.  In measuring curtain arrays for them and others I have never seen one fail to meet spec.  I suppose that an Amateur installation that doesn't allow for acres of undisturbed symmetry wouldn't be as good. The big difficulty is in keeping common mode currents out of the measurement setup.  Measurement errors become evident when lead dress variations lead to non-repeatable measurements.
After you've incorporated the most practical choke solution, remember that common mode current is not lost, but radiates, somewhere, at some angle.  Recall Maxwell's famous deathbed statement: " RF gotta go somewhere, chaps."
73 de Norm W1ITT

Tom,
I did not use any balun on 75 or 40 for decades. My max power was only 700 watts though and I only got a little burn on
My lip at times from touching a metal desk mic …😉
The bottom line is whether it is important to keep as much RF out if ghr dhsvk as possible or to just wing it.
With the old tube receivers, the RF had little effect, but I hear that modern wide band SDR receivers hooked to big led displays, keeping the shack “quiet” had benefits…

😂😂😂 Your question about using a small cooled choke in-line reminds me- perversely of the old joke about the kid who was cautioned about his behavior on a personal subject leading to blindness and he later admitted to continuing the doubtful practice only until he needed glasses…😉😂😂😂
Seriously, the use of reactive chokes has a significant risk of increasing common mode currents as well as the hope of reducing them, as intended. See the zG3TXQ article I just posted. I would skip it, myself and go with the ferrite core wrapped with rg400

If you look at G3TXQ graphs, 25 1020-31 beads will provide 500 ohms of choking at 80 meters snd the black tracer means that it is an effective 50ohms.
However, think about that bleeder resistor you put in your Hv supplies snd how you decide in it’s value and power rating.
10K across 3kV will cause a lot of heat, while a 1Meg high voltage resistor will be much cooler.
The parallel is that, like a dropping resistor  for a plate volt
Meter, you may only need 50 micro amps and ideally, the common mode current will be close to zero.
Putting a few beads on s feedline will be effective if you were not going to have much common mode current anyway and it will therefore be cool enough, but if the head voltage causing a common mode current us high, then that 500 ohms will be a hot mamma until the ceramic blows…😉
So the answer is- who knows?
Jim Brown will tell you to design for the worst case scenario.
Like your choice to support your new Fan with 3/8 Dacron, it will appear to be overkill to guys who use poly baling twine from the farm store, but you are ready for more scenarios and I like you’ll chances to get through a cold icy New England winter (are there any other kinds??😉😂

RG-400 on a FT240-31 or better- two hooked in series is the gold standard for performance.
RG400 is rated at 1900 volts and 3000 watts CW up to 100mhz, so at HF it can handle all you like.
Jim Brown also swears by awg12 Teflon insulated silver plated copper paired with tape and wound the same way as rg400, but I really like RG400 .
RG141 is similar but stiffer and it uses steel solid core with silver plating. RG400 easier to wind in my own experience, having tried both.
I put my FT240-31 chokes in a pvc box but Jim Brown advises against it. If vents are provided, it will cover his objections kn that though.
The small FT-240-31 balun scan also be dipped or otherwise sealed and mounted on a HDPE plate and it will be lighter than 25 beads on the RG11 and much more effective.
Review the pics I posted for ideas on that method by a friend of Jim’s from 6 Land.
73, MB


http://www.rosnol.com/upload/product/RG-400%EF%BC%8F%EF%BC%B5.pdf

Hi Folks,

My comments are based upon experience (some of it bad) and a bit of theory.

I believe what we are discussing is minimizing feedline radiation due to unbalanced feed from coax to a balanced dipole.  If you run the feedline away from the dipole perpendicularly for a good 1/2 wave or more to get it out of the inductive field, then you may not even need the "balun". Equal but opposite currents would be generated on the feedline on the outside of the shield but cancel out. I have done this in the past and minimal (milliamperes) outside feedline current was measured taken at several points along the feedline (important!) at 1 KW.  

Years ago I had stacked KLM yagis up for the high bands which used ferrite based baluns.  After a lightning strike VERY close, I noticed the F/B ratio on two of the antennas had dropped from the usual 25 dB or so to around 10 dB the day after the storm.  No visible damage anywhere but the SWR had also gone up a bit so I decided to replace the baluns.  That fixed the F/B problem.  I sent the baluns back to KLM and their analysis was that they had become very lossy.  I mentioned the lightning and they said they had seen this before.  My guess was that they had ceased being baluns and the feedlines now became part of the antenna destroying the pattern.  These were 5 KW baluns with extra ferrite too!   I never put more than about 2500 watts into them. This happened once again and then I went to air wound solenoid choke baluns on all the antennas, never had the problem again.  Anecdotal for sure but.....

On solenoid choke "balun" design, I use an HP 4815A vector impedance meter to optimize the # of turns on 6" PVC.  I have 2 of these on my 2 stacked 40M beams.  To optimize this design, I connected the meter to the shield on either side of the coaxial choke and adjusted the # of turns to get the parallel resonant frequency to 7200 KHz.  It took 12 turns of RG-213 to accomplish this.  At resonance the impedance was 30K ohms and purely resistive.  At 7100 it dropped to about 16K and was slightly inductive, perhaps 10 to 20 degrees if I remember correctly.  At 7300 it was slightly capacitive and about 15K ohms.  Not bad.  Clean text book pattern with no measurable feedline currents.

Having not completely adhered to my no outside ferrites rule yet, in 2010 when I put up the latest 4 stack of 10E log periodic antennas, I used two ferrite based power combiners outside mounted up the tower to reduce the feedline count  coming into the shack.  I used this combiner set up for several years with no issues until another nearby lightning strike.  The next day when I used the logs, I blew up one of the combiners after a short transmission which started out fine.  I remember watching the SWR creeping up thinking maybe some water got into something until it went to infinity.   The combiner had split into a number of pieces and looked like it was overheated since plastic enclosure it was in had started to melt.  I wound up running all four transmission lines into the shack where the ferrite combiners are.  It all gets disconnected when storms come through.  

This is why I will NOT use ferrites outside.  

Back when I designed high power SS amps professionally,  the higher permeability ferrites would sometimes get permanently magnetized if an output device failed and sent a high peak current through an output transformer.  This would skew the hysteresis curve of the ferrite and render it lossy.  The ferrites would still work but run very hot.  Avoid ferrites if possible.  We eventually changed over to powdered iron which is much less susceptible to this failure but it isn't available in a higher permeability unfortunately.

-Chuck

That is very interesting, Norm.
No doubt, high power broadcast transmitters operate in a different world from Amateur service.
I would like to know more about the feedline systems you
mentioned being balanced lines. I had assumed that the feeds were differential in
Massive rigid gas filled heliax feedlines.

The -26dB spec would make the differential power at 1/400 of the differential power.
In an amateur transmitter, that would be 250mw  milliwatts per KW of Differential power delivered to s ham antenna- not much radiated, but may be adewuate amount to tolerate getting into the shack maybe.
So do these big rigs use large current baluns to convert balanced to Differential feed?

I can see what you mean if the balun has a -26 dB leakage into the common mode.
In the case if suppression chokes, however, the high RS value
Prevents the current to flow significantly and the only significant RF left is in the
Infrared
Spectrum and measured in heat dissipated, not Hf and for low power like Hams use, that
might be a good solution to
The common mode problem.
Please tell me
More about the baluns use on these mega transmitters though. I find it very fascinating.
Any pictures to share?

That is very interesting, Chuck.
I assume that your combiners were transmission
Line devices and I can see how they might be destroyed if the reactances dove to nothing. Those are inherently reactive applications where low loss ferrites are essential.
What kind of ferrite did you use?
Have you ever used #2 powdered iron for that kind of combiner?
You certainly have a great deal of experience and I would love to know
How you solved the combiner problem?
I used custom coaxial designs for my moon bounce arrays in the
Late 70s, but that was 2meters where a wavelength is 82-84 inches snd my application was dividers, not combiners, also, do far different from your 40 combiners. 73, MB

Mike and all...
In the HF broadcast world, balanced line is still used. 
(although I'm unaware of any new SWBC stations being built and some of the ones that I built have since been taken down.)In some installations the "open wire" is actually copper tubing an inch or so in diameter, hung from insulators.  Some is multistrand alumoweld cable of the sort that would make darn good guy wires on most of our towers, also hung from insulators. The American transmitters seem to gravitate toward 50 ohm coaxial outfput, fed through switch matrices depending on what antenna was wanted, then often to  a broadband transmission line balun outdoors, then balanced to the curtain.  Other folks use balanced tanks at the outfput of the transmitter and go from there, into balanced switch houses and then out to the field  Most of the world operates at 300 ohms but, very Britishly, the Brits liked 330 ohms.  One used to see big oil filled baluns with presumably ferrite cores, but now the transmission lines rule the roost.
I was always bad at photographs, sometimes because I was never  a camera nut and sometimes because the end users were not always happy about picture of their installations, even though all the hardware appeared in manufacturers' brochures.
Back here in the Lower 48, I content myself with the almost 500 feet of open wire  (540 ohms) with number 12 Flexweave and feed it with either link coupled   tuners or balanced L nets with ferrite at the 50 ohm input.I solve the bandwidth problem on my 80m phased array by having a tuner down on CW and the other in the SSB DX window and big honking knife switches.
By the way, I appreciate Tom's habit of bringing his projects into the room.  Plenty of food for thought and education, and even some of the folks who aren't into this level of construction can learn along with the rest of us.
73 de Norm W1ITT

Mike & company,

The "combiner" is a 1:2 impedance ratio ferrite transformer to transform 25 ohms to 50.  I haven't read Sevick's book in years but I believe he covered this design.The top two 10E log antennas are fed in phase and in parallel with equal length lines to the input of the 1:2 transformer.  Same with the bottom two log periodics.  To run all 4 antennas I use a third 1:2 transformer where the output of the two combiners are combined.  This way I can drive either the top two antennas or the bottom two antennas separately or all four together all with 50 ohms.

Previously the combiners were on the tower.  Now I run all four equal length feedlines into the radio room where the combiners are now.  I disconnect the feedlines from bulkhead connectors on my house in case a storm is a possibility.  I do this with all outside connections (rotor controls and other feedlines) for total isolation.  Problem solved.

-Chuck

Chuck, I was just thinking- have you considered a system of linear transformers for feeding your logs?

What I mean is that you build up a system of 75 ohm 1/4 wave Q sections for each of the 50 ohm feeders and switch them in for different bands.
If it were just-say 20 meters, it would be simple. Two 1/4 wave stubs feeding a Tee connector. You would have two 100ohm loads in parallel and in phase.
If you wanted other bands, you just use high current vacuum relays to switch in stubs that would give you 15meters, 10 meters, etc.
I know this smacks of Rube Goldberg (I am an original cult member😉😂) but it would have the virtue of being relatively immune to EMP attack.
It would work. I am sure. Used something like it in my 80 element Moonbounce array of 16-5 element beams…. Talk about a tribute to old Rube?!!😎😁
Comments? MB

Thanks Norm, very interesting rundown. No doubt, that 1 inch copper tube open lime is very low loss but the  rub being at the balun.
I really like the synchronized twin L network tuner that someone published and I have accumulated most of the parts for it have a couple of nice RCA rotary inductors for the inductors.
I would like to switch a vacuum variable across either end to allow the impedance match to extend above and below 50 ohms. Any suggestions appreciated on that.

Tom is a great contributor- not only for his large history as a builder snd experimenter, but his knack of stimulating the discussion to improve the art by allowing the vast experience of members and the creativity that goes with it, to make this forum a great place.
Design and experimentation and creative solutions have always been my meat and drink, so this is great fun. I feel like I learn a lot on here and on Class E Forum all the time.

I appreciate the answers, Mike, Norm and Chuck!

Yes, these threads will outlive all of us on the web.  I could be wrong, but I think 97% of the hits on this forum are from Google and web based search engines. That's how some of these threads get 100K + hits.  We learn and the world learns too.   Goto:  Home, Users Online,  Click on: 67 Guests, 3 Users (1 Hidden) to see the hits over the last 20 minutes or so... There are sometimes hits every 10 seconds  - mostly to old topics...absolutely amazing.

I have a few more questions that are still fuzzy...

1) Will a balun do the same job if mounted 1/2 wave away (or any 1/2 wave multiple if the coax is long enough) from the antenna feedpoint?  Or why is the antenna feedpoint the best spot, if any?  It would be so much easier for servicing if 1/2 wave away worked as well.

2) Back to Chucks balun idea...can the MFJ-259B ant analyzer work in place of an HP network analyzer to find the resonant point of a coaxial solenoid wound balun?  It appears the distributed capacitance from the turns is creating the capacitance, not an external capacitor.  Maybe if this balun is operated strictly within its 7.0 - 7.3 resonant design with 15K-30K impedance, it can work well. In my case for the delta loops I'm looking at 3.8 MHz so it would be a big coil. I'd like to try one at the 1/2 wave away point as discussed.  

My openwire experiment feeding both loops, one as a driven and one as a tuned reflector stub did not work as well as it did with coax in the past.  It had forward gain into EU, (+10 DB over the fan dipoles) but the f-b was lacking.  I brought the open wire closer together, 6" spacing but still poor f-b on the air. The antenna beacon off the back nulled sharply, however.  It's like the band has been broken.  The locals are down -20 to -30 DB as desired, but the far away W4s should also be way down but are not. Strange.  I'm hoping a forced driven feed coaxial system will create a tighter pattern.


# BTW, I ran a 1500 watt carrier thru the new broadband fan dipole for a few minutes. The swr stayed at 1:1 on 3785.   So it looks like the RG-11 and nine stacked ferrite cores are working FB. I will use this as a baseline test for lightning or other damage.


T

Tom,
We should use the term common mode choke to describe what I have advocated and the purpose is to prevent any common mode current flow on the feedline.
Putting the first one 1/2 Wave from the feedpoint is like leaving th barn door open and them relying on the stock femce gate to keep the horse “in”. He is,obviously already “out” 😉.
The second one I advocated was there as a secondary backup, not a promary solution, to scrub any remaining current at a place where the standing wave would present the lowest voltage, rather than at 1/4,wave where it is max voltage and impedance.

Good news about the tests on the new wideband fan. Run a contest through it with hours of operation and I will be convinced, however…😉.  Still- of there was a big problem,it would have been apparent already…
You have achieved a lot already on that nice 80 meter fan…😎 Mike

If you want to go air core coaxial balun, the work has already been done.

http://www.k1ttt.net/technote/airbalun.html

I will add, you want NO metal near the coax.  It will increase C and cause the balun to be less baluny....  Balunistic?  Whatever.

If you are still considering the ferrite, the 4 inch cores work quite well with LMR600.

Just don't exceed the bend radius.  They look goofy but they work well.  And LMR600 will take anything you've posted pics of....

I've not lived where lightning was a big threat....  So I defer to Chuck and his experiences.  I guess I will be dealing withightning now, though.

--Shane
WP2ASS / ex KD6VXI

Mike,

No on your idea.  As you said, Rube Goldberg!  The solution I did was very broadband requiring a 2:1 frequency range for the log periodics and that could only be accomplished with a broadband approach hence the use of ferrite transformers.  Now safely within in my house, no worries!  Totally different from the transmission line based approach used on VHF where it makes sense.

Tom,

The MFJ will not do the measurement you desire.  It's a 50 ohm based device.  A really great way to do this is with the Nano VNA.  I have one and it pretty much agrees with my HP stuff although really high impedance values make it go nuts.  If you get to that point, your coaxial "balun" is good.

As far as a 1/2 wave away, you would need to make sure everything is very symmetrical to the 1/2 wave point to avoid picking up common mode currents.  If you are that far away, with symmetry, then the balun may not needed anyway.  

Comment:  Given these are dipoles, if 80 to 90% of the power gets to the dipole, why worry about a small fractional dB that might slightly distort the pattern?  It's not a high gain yagi that needs pattern preservation.  (like the VHF guys that need a clean pattern to reduce terrestrial noise)

Mike,

Yep,  balun, choke and unun  ....  I often use them interchangeably out of laziness.   I am dealing with chokes here mostly.

Shane, I do intend to use a combination of air core chokes and ferrite beads on both the fan dipoles and the delta loops. Whatever I come up with in the end it will talk, caw mawn... ;D

Chuck,  OK on the MFJ-259 being 50 ohms and not a good tool for the high impedance job.

The fan dipoles are turning into an experiment to see how clean and effective I can make an antenna for 75M.  It covers the whole band reasonably flat and I figured it could also be made as quiet as possible. During the day, the S meter sits at zero... so it's a quiet neighborhood to start with.  It is now my main antenna for local 75M work and will get used a lot, so WTF, might as well. The loops are going to be the real challenge, pattern-wise.  There are a lot of possibilities now for the dipoles and the loops since I've learned a lot of things from this thread.


It's been one of those days...  I took Yaz for a long walk and a thunderstorm rolled in.  Got drenched beyond recognition.

I get home and figure I'd do some coax feedline work by putting some connectors on the RG-11.  It is a slow, difficult job.  After doing a great job two hours later I realized that I forgot to put the ferrite beads on first, before the connectors.  They will not fit over the connectors and I have no clamp-ons, just a box of donuts. Took out the dikes and madly snipped off the connectors to start over.  Am I the only one who does stupid crap like this?  And I reminded myself this morning to put the beads on first.

My Dodge truck blew a brake line.  Gawd darn salt on the roads. That will cost a cool $500.  To add to it, it's been near 100 F.  The summer heatwave.

No worries.

T

Hi Chuck,
😂😂😂 Ok, that was a test balloon to see how much you loathed Ferrite…😉
I get it, I would walk away from Rube on this deal too, but hey- you seemed unhappy with that great Sevick designed Ferrite transmission line transformer, but it was only the lightning- in the end and we all fear and loathe that destroyer…
I am sure that you will never see another fsilure with your protocol, by the way.

I told Tom the same thing about a radiating feedline on a no dorectional antenna that aims high and short. Of course, there is local rfi noise to consider and Tom did say he wanted it quiet and that feedline is a good way to pickup any stray noise maker…😉. MB

A friend sent me his interesting explanation of currents on the shield:


"I see guys talking about currents on the shield. A balun will not eliminate the current because they are in the near field. Picture the coax as 3 conductors. The center conductor, the inner shield surface, and the outer shield surface.  The rig drives the center conductor, and inner shield surface. The common mode choke tries to force a balanced out of phase current coming out of the coax so the antenna gets a balanced drive. In doing this drive current is isolated from the outer shield surface. You have unbalanced drive if the current goes down the outer shield and screws up the radiation pattern. Picture the common mode choke in this case is an RF choke in series with the outer shield because flux is balanced between the center and inner shield as long as the antenna presents a balanced load.  So if you have cable with a crappy shield life gets unruly because it will leak.
It was hard to wrap my head around this learning about transmission line transformers."

Tom,
Your friend has a lot of it right, IMO, but a good choke greatly diminishes common mode current- or the potential of it,  and the near field is intense because there is the antenna currents as well, but the thing that helped me understand it was to stop seeing the choke as merely a “lossless” inductor, but as a very lossy device that has inductance and a great deal of loss reactance u” as well, and like a large dropping resistor for s voltmeter, very little current flows through it, and the current that does gets turned into heat, not transmitted or radiated.
I think that you understand the basic choke balun or 1:1 guanella balun function.
The idea of a common mode choke balun is to make any common mode voltages see a very high complex impedance which reduces common mode current to very small levels.
The differential mode currents are indeed in the center conductor and the inside of the shield.
I do not think that the shield is like the perfect waterhose that is a perfect barrier at all frequencies, though.
Think about the screens used in rf shielding an HF amplifier. As long as the wavelength is large compared to any holes in the shield, it can be effective.
As you go up in frequency, the grid has to be smaller and smaller to be effective.
That is why coax used for Hf can have less dense shielding and still be effective, while coax used for satellite (3.5GHz or higher) uses solid shield or double shield plus foil. Common mode chokes stop currents at the end of feedlines where the inside and outside are connected together. The reason certain Ferrites are more effective is that they have high permeability and high loss resistance and the vector sum will have a very high resistive component that is most effective in killing common mode currents before they can start flow9mg on the outside around the open end of the line.
If you look carefully at the K1TTT data, you will see that the impedance is positive in some ranges for certain coils and negative above a certain frequency and that frequency is the self resonant frequency of the choke. It therefore gradually stops being an inductive reactance and becomes more of a coupling capacitor that actually can effectively couple common mode current to the outer shield of the feedline.
This is why you cannot just make a huge coil to make it better, because above self resonance, it will become worse and even harmful.
Inductive coils actually work as single band chokes at or above 7mHz. You need to custom wrap them for a single band for best performance well below self resonance and where inductive reactance is maximum.
The trouble is that they are useless for wide frequency range and the impedances are not very high compared to FT240-31  RG-400 choke baluns.
If you want to make a single band 40 meter coax choke balun, or single band higher frequency bands with proper design parameters.  They can give 500-2000 ohms for these applications. This seems evident based on the K1TTT data.
I do agree that a coil of coax will be cooler than an inadequate choking impedance ferrite common mode choke because the currents that result from the low choking impedance can over heat the bead(s).
Jim Brown and G3TXQ explain all this in their articles.
73, Mike

I really envy you guys with tall tower antennas and space away from city power lines. It's very educational to read and understand these experiments and gratifying when they work so well.

Yeah Patrick, A lot of us have unfulfilled fantasies combining these two photos in one location. Trouble is, if you get the first one- property laws prevent the second. We all make compromises , but in my dreams!… 😉😂😂

In Mikes second picture, the mountaintop shot, that six-bay sidemount FM array in the back is one that I built years ago when I was doing FM antennas by the truckload.  I'm fortunate that I've been able to make my living playing with transmitters and antennas and getting paid for it, and flown all over the world.  Just the same, I'm happy with my 70 foot tower and 100+ foot pine trees in the back yard.  This fall's project is a 9-circle receive array for 160, 80 and 40 across the trout brook in my swamp.  Common mode is the potential problem on that as unwanted pickup can mess up the directivity quickly.
Again, I'm enjoying the continuing education facet of this thread.
73 de Norm W1ITT

Norm, that is fantastic! I screenshot that pic from Google. The caption said it was from New Mexico, but I posted it because it embodies all a radio guy dreams of having in his backyard on that mountain.
The Martha’s Vineyard estate is more to my XYLs delight and as out if my reach as the amazing
Mountaintop antenna farm.
I wondered if one of the guys on here would recognize it when I posted.
It constantly astonishes me that there are centuries of radio engineering expertise among the members of this forum. AM Heaven!😎
Thanks for letting
Me know that you were one if those guys who did that amazing array close to the heavens . 73, MB

Chatsworth Peak, California is awesome as well.

Even private homes got in on the antenna farms for commercial profit.

There is a TCI Log pointing at the Central America / Caribbean area there.  It was a single xmitter site using the last Amplifuzz on shortwave.  Now has multiple xmitters connected and running simultaneously so the poor engineer doesn't have to climb the mountain twice a day.  Jim appreciates that!

--Shane
WP2ASS / ex KD6VXI

New question concerning tuning two identical antenna elements:

Let's say I have two identical 75M delta loops  spaced 40' apart on a boom.  I want to resonate/tune them in place for 3.790 MHz -  to make each close to 75 ohms J0 at each  feedpoint bottom.   I can climb the tower and access each one (no feedlines attached ) to add or subtract wire.  After tuned, when I connect the coaxes, I would like both coaxes on the ground to read 75 ohms J0 so that I can feed them directly with the proper phasing lengths of coax.

Should I tune each loop alone without the other in the field?  -  Or should I try to jockey back and forth and tune them both to give 75 ohms (both in place) at the same time?  I wonder about mutual coupling of the two loops.   I know if I tune them each alone and then put them together they will pull off freq.  Or is this OK?

I could lower one and get it out of the field or even clip lead lengthen it so that it is invisible while I tune the other.  Or tune each one and get them BOTH to read 75 ohms at the same time.

Which is the proper way to do this?  I won't contaminate the question by saying how I did it in the past... I just want to know the proper technique..  I've  always used parasitic elements, thus all is tuned in place at the same time.  But I don't know about driven elements.

Is this a clear enough description?

T

You're running 75 ohm coass from each antenna to ground level, correct?

--Shane
WP2ASS / ex KD6VXI

Shane,

Yes, after they are each resonated to 3790 in the air, I will attach a 150' long feedline from each feedpoint to the ground level for driving with RF..    I will use my MFJ-259 antenna analyzer at the center bottom feedpoint of each loop (at 120' high) to initially tune them.  

T

What are you trying to achieve with this array? You are are about 3/10 wave apart - nearly long enough for a 3 element quad, but you are talking two

You must have something special in
Mind to go to the trouble.
I guess you have shorted stubs that are adjustable for tuning?

Hi Mike,

This spacing worked well in the past when I fed the loop driven element with RG-213 and then tuned the second loop as a reflector using the other RG-213 coax as a stub.  I am trying to achieve?  a bodacious low angle signal at about 25 degrees take off.  ;D

In this case I wish to make identical loops that are each forced driven with equal length 150' RG-11, hopefully to a 75 ohm 1:1 match for each loop..   One of these  equal length coaxes  will get a 90 degree (or whatever is needed) phasing coax to make a unidirectional beam pattern into Eu.  Switch the phasing coax to switch directions. (USA)

So, I want to initially tune the loops each to 3790 by just trimming the loop's wire length. Once I get 3790 for each, the coaxes get attached.

I need to know when I do the initial tuning do I tune each loop alone or do I keep both loops in position (spaced 40' apart) and tune them that way, to take in account the mutual coupling detuning effects?

T

Tom.. Your best bet is to tune one element, then lower it out of the field of fire and tune the other to make it look like a twin.  Then put it all together and combine things with a phase angle of your choice.  You'll probably have to use an L network at the common point to get things to come into match.
The mutual impedances are not the same for driven elements as they are for elements that are parasitically coupled.  In broadcast work I have measured FM panel arrays in 3- around and 4-around configurations, as well as arrays stacked.  And to make it worse we had to maintain circular  polarity in cross dipole panels.  It involves a fairly complex  drive everything network analyzer setup, matrix math and just plain screwing around until it works.
Check out ON4UN's book, Ch 11 on "arrays" and Ch 12 on "other arrays'.  The first antenna in Ch 12 is a bit like what you are doing except that it involves a 180 degree phase shift to make a Figure-8 pattern.  I know your elements are loops but it's all the same.  I use something similar on my open-wire fed array and I like the bidirectional pattern because it keeps those inland boys reminded that I'm there.  High angles are suppressed and the main beam is shoved down below 30 degrees.  Take notice of one of the first charts in Ch12 that shows the effect of element spacing on feed R.  I space at 1/4 wave.  I use a separate receive  antenna so I don't worry about front-to-back in the transmit array.  There are a few good ways to skin this kitty...  ON4UN's book did a lot to raise the bar for lowband aerials.
73 de Norm W1ITT

Norm,

Tnx for the info! OK on tuning the loops separately with the other one out of the field.  That's not what I was hoping to hear... ;)

Once both are tuned, how much do you think the impedance will change when the second loop is hoisted back into position?  Starting at  75 ohms J0,  if it changes like down to 50 ohms, that is a built-in swr of 1.5 :1 with the RG-11.   Whereas, maybe they can be tweaked for length and pulled back to 75 ohms or 1:1 each when in position.  

The last time I did this I tuned each loop with the other in the field. I eventually got close to the 50 ohm match for each that I was looking for at the time. I'm trying to be cautious cuz it seems like something that can be controlled to the benefit of a better match.

On the other hand I have seen guys stack Yagis without changing anything to do with tuning.   BUT... I remember  an antenna manufacturer, I think it was M2 but not sure, that offered to optimize my two store bought Yagis for stacking. He insisted that the mutual was strong enuff to require this.   Maybe Chuck will chime in with his experience and practice on stacking.  

I plan to make the climb as soon as the choke materials arrive.

I did expect to have to match the coax junction of the two loops to the run to the shack, however. An L network or 1:2 step down transformer would do.  (75/2 = 35 ohms  X2 = 75 ohms to the shack )

T

Ok, Tom. Sorry- my brain skipped a cog and I put the array on 40 meters. 🤪
Ok, you have about 0.15 wavelength spacing and I see how you made that work with a reflector.

I am curious, however, why you are not just making an array of phased verticals if you want a low angle signal. Seems like 4- 1/4 wave verticals can be phase shifted to give several cardioid directional patterns and with a good ground under it, the radiation angle will be down around 20 degrees, I am thinking.
Why are you not using phased verticals?
What is the height of the loops?

Hi Mike,

Been there, done that.  There was a time when I had an 18,000'  spool of  #5 copper clad aluminum wire. I went thru the whole spool trying every antenna known to man on 75M with a 150' tower. The bottom line is a high horizontal Yagi or loops are the clear winner.

My loops are at 190' high, average height about 130'.   They are by far the best antenna I've ever used on 75M for DX.    The verticals also have their problems. You need a very large, clear area clear of buildings, etc. The ground should be good as well as an elaborate radial field.  The phasing/switching  is complex unless you buy a ready-made system.  You need four verticals.  They can be noisy due to power line coupling vertically.   In general, the biggest signals on the 75M band DX-wise are high Yagis or loops that are 1/2 wavelength above ground.

So that's why I've stuck with the horizontally polarized loops on 75M for so long and want to get this same system working well again.

I received my ferrites today so ready to go.  I will take Norm's suggestion and tune each loop individually.  This way they will both be the same wire lengths, have the same length feedlines and resonate at 3790.  From the ground level I can then add force feeding or tuning a reflector with the coax and a capacitor.  Lots of options.


T

Hi Tom,
Thanks for the rundown. I get it with the verticals requiring a lot of phasing control and of course a large ground shield is essential for the kund of performance you are wanting.
Just one more question, as a follow up in my height inquiry.
Have you ever considered vertical half waves suspended from a non conductive cable like dacron rope or phillystran and then feed them like a LPDA with open feeders.
At 150 feet at the top, the bottom of the vertical hals waves will be about 25 feet above the ground, but the takeoff angle should be very low because of the vertical orientation and ground losses will be less than a monopole above a poor ground screen.
I have toyed with this a little for 40 meters because I have only 80 feet to work with, but it is on a back burner.

I have been meaning to tell you about a wire beam array I built for 20 meters when I was young and poor that worked very well.

I built an extended double zepp for 20 meters and then I put a pair of reflectors behind the driven elements limed up with the outer half wave and a second pair of directors in front of the driven element - each about 0.2 wavelengths from the driven extended double zepp.
Then I fed it with 36 feet of OWL and shorted the end with a sliding short and then tapped up the line with a folded half wave coaxial balun.

I was using an old SBE33 that I rebuilt and a 4x807 GG amp (told you I was poor😉).  I was putting out 400 watts into that wire array and it beat local guys with 1000 watt amps in Florida where my Father-In Law lived and a guy from Venezuela called me one day after we completed our QSO and said I had a very strong signal in that country.
My pitiful array was very small potatoes to your 150 ft loops, but it was great experience in how old antennas can be adapted for new uses.
I actually got the idea from some 10 element 2 meter antennas that I got from Russ Farnsworth who is the inventor of the Farnsworth Method of teaching CW. He marketed his tapes theough Heathkit company.
Russ was blind, but he was amazing and he did a lot of work in spite of his disabilities. Sorry for the digression. It happens to old guys that they see something new that reminds them of something from the “old days” 😉
73, Mike

Hi Mike,

FB on your 20M collinear array with reflectors and directors. SBE 33 and quad 807s...  ;D ;D    That's a coincidence cuz I built the same antenna, but a little larger back in the early 90s.  It was a stacked and collinear, 36 elements.  It had a narrow beam fixed on Eu.  That antenna sure talked. I had a 20M reference dipole at 30' high and the array was usually about 20 dB louder.  Describing it I used to say it was a curtain array 90' tall and 300' wide. I still have it rolled up and stored.  I'd like to build something smaller, like maybe  2 over  2, over 2, over 2  for 20M and feed it with openwire to show huge gain on 15/10M.  I modeled it out already and is enchanting.  Lazy H's stacked or whatever. Still thinking.

BTW, I did try a 75M TCI  LPDA design in the vertical plane. It was about 10 dB weaker than the high Yagis.  I figgered it was lack of ground screen.  

Today was a crazy day.  I got tired of watching it climb to 99 F and not going out to work.  Screw being a pussy. I went out at 12 noon, climbed up to 125' and climbed down at 3:30 PM at 98F. Finished rebuilding the feedline and feed junction for the triple 40M Yagis stack.  It was finished, finally!!   It took me two months of work to repair the middle Yagi aluminum damage and clean up the feedline contamination.  I measured each Yagi and found they were all within 20 KHz of each other. Nice.    With confidence I walked into the dog house to test the full array for the first time. I expected 1:1 swr.  It was 14:1!!!  NOOOOOOOO!!!!!!   I started to get depressed thinking of what would be required to take them down again.

After 30 minutes or so I went back and tried to figure out what was wrong. Did I make a wiring error?  Then I realized that I had the wrong cable plugged into the 50:75 ohm balun. I was measuring some old 6M cable from 10 years ago.  

I hooked it up properly and there was nothing!  Did my MFJ-259 crap out?  No, it was working. The swr was 1:1 at 7.150 for the stack. In fact the stack is more broad banded than my 40M wire dipoles. I think the fat aluminum full size elements all tied in parallel makes it so broad.  The reflectors are tuned for about 6.800 so the swr is near 1.2:1 from 7.0 all the way up to 7.3 MHz.   The f-b and gain drops off cuz the reflector is fixed.

I listened to the 40M band and see the W4s are weak off the back and the locals are weak due to being a low angle antenna at 13 degrees.  I tuned in a few Euro stations and the stack was always louder than on the 40M dipole at 105', as you'd expect.

So far, looks like the stack repair is going to work out FB. Gawd my feet are really sore from standing on the rails for 3 1/2 hours.

So tomorrow another climb -  but this time to hoist up the new RG-11 feedlines to the 75M delta loops. If I can get this done despite the hot sun, I'll be close to completing the antenna projects. The 20M plans will have to wait.  That 500' RG-11 roll was a great deal for $85.  It feeds the fan dipole and now the delta loops.  All gone.


T

Tom,
Thanks for the report on the vertical LPDA. They are indeed not known for forward gain or F-B compared to a good YAGI array. Your remotely tuned end fire array will allow the tweaking to optimize on the fly once you get the phasing figured out.

You have my deepest admiration for your grit, getting out in this Summer hell storm..😬
It has been decades since I was up over 100 feet on a tower and 10 years ago, I decided to stop because my back and knees made it too painful.
My pitiful array of 6 elements on 20 is not to be compared to that array you put up, but it was great fun, lacking only rotatability.
I am content with a Teledyne T8 at 65 feet now and am focused on 160-40 meters antennas.
I am ready to put up 80 feet of 25G on a home made insulated ball joint and will run 160 and 80 meter verticals- inverted Ls on it. I have been considering a skeleton disk-cone with 8 wires around the tower lately which should cover both bands.
My ground will be 7000 feet of PE insulated 14awg dog fence wire groundstapled down in a 100ft circle around the base. It is all aline on a little hilltop 300’ from my shack.
Nothing like your impressive arrays, but there is hope that I can work some DX when ole Sol calms down in a few years..😉

I have enough space for two 350’ short beverages crisscrossing to cover NE, E, SE, and SW directions.
I wish I had your energy, but at 74, I have slowed down and cannot do what you did today without an appearance in the Obits…😉😁
Thank you for the rundown.
Looking forward to further reports.
I like your results on the RG11, so I have decided to feed my 80 meter fan or cage
( not decided yet) with this lightweight cheap stuff. I have two 500’ spools, so it all seems possible.
I am considering that 3 ft spaced cage because I have exactly 130 feet between my two 45G towers. I have to mount it low at about 55 feet, so a fan would put the lower one down at 30’ at the ends. I will run some tight Dacron plus 10ga copperweld so I can support the middle with about 5-6ft of sag and the middle is right by my shack, so the feedline will be short and light.
It will be interesting to compare bandwidth. I suspect that your fan is better though..

73, Mike

Mike, FB on the PE insulated dog fence in a circle as a radial ground plane.  That sounds like a cool project with the big tower.


Here's some pics of the feedpoint RG-11 I made up today for the 75M delta loops.  Look closely and you will see the dacryon cord supporting the 12 ferrite beads. The beads will be supported by the center insulator later.  And I use a pipe hitch, like a hangman's noose, to support the coax itself.  The upper portion is where the connector resides and is quad sealed for weather.  I'm hoping this arrangement for the two loops is waterproof as well as strong to support the weight of the beads and coax.  The coax will be routed to the tower and tied to a tower leg all the way to the ground level. Maybe 40' of free hang.

T

Pic 1-3:  Notice how the beads and coax are independently supported, putting the least amount of strain on the RG-11 coax.   The RG-11 coax is not as rugged as RG-213 for strain, so needs extra precautions.   The weatherproofing uses four layers:  33 tape, rubber clay tape, 33 tape and then a layer of liquid tape.   I made my own RG-11 connectors using a 3/8" copper tubing sleeve and hose clamps.  Plenty of D-Ox.  The output leads are soldered to the sleeve and copper inner conductor.

Pic  2: It's so hot that I gave Yaz a hose spray down.  He actually enjoys it and runs back and forth thru the spray. Stops his panting right way.

Pic 3:  The 75M fan broadband dipoles are finished and in service. It's nice to put things to bed.

Pic 1:   The 40M stack is finally finished. Now testing - all work to be done on the ground.... YAY!  Look closely at the center Yagi to see the coax coil and connections finished yesterday.  I DO NOT want to climb up there again hopefully for a long time... ;D    60', 125', 185'  fed in phase, fixed on Eu..

Pic 2:  This is my portable tower workbench - the back of the Dodge truck..  I drive it from tower to tower as needed. I just cleaned it but it can look like chaos personified after a job.  

Tom,
I chose these three images to make my comments, not a little because of that dignified and wise looking “Good Dog” you included. It is easy-in this photo to see why you talk about him all the time. Looking into those soulful eyes, one can see why we all love dogs, specially older ones mentioned as one of the three finest things in the world by Tom T Hall in his hit song-
Yaz actually looks like a younger dog, but he has that ageless look anyway.
https://youtu.be/pQAk-xYxvVo
I can see absolutely no way to improve on Yaz. He is the quintessential “Good Dog” we all love as a faithful companion… 😎😁

But on to antennas:

The packages look water tight and secure for the feedlines and  that Dacron braided line is extremely strong, resistant to UV and does not stretch like nylon.

My only question, is a question I ask when I see ferrite suspended in tue weather where it can meet with many challenges.

In those stacks, I wonder about water finding its way down the opening in tje top bead. My own compulsive nature would seal that top where the feedline emerges to prevent an easy entry for water.

Then at each joint, the joints are open and that probably is a good thing to allow any moisture that got in from being captured in there though my own compulsions would likely wrap them with scotch 33 or 88. Then the bottom where there is what looks a connector seems to be sealed off so any water in that space might not be able to get out.
If the bottom was mostly sealed and the top open and you started getting freezing rain, the prospect of a icicle forming in the stack seems possible.
Maybe I can ot see it properly, but I,would,be sure that entry from the top was very difficult and exit from the bottom emulates the old inverted bucket method for waterproofimg a lot of outdoor connections and preamps, etc…

Third- that is a nice pic of your Fan Dipole. That needs to be published more thoroughly, IMO with more details on dimensions and  some SWR plot pics, etc. that is a great “Every Ham’s Antenna for 80 meters and I think that your application of the 75 ohm lightweight CATV-Sat coax is key to making it supportable.

Nice work- specially you- Yaz and you are doing pretty well yourself, Tom with minor reservations visa vis my questions.😉😂😂😁
73, MB

Mike,

I'm really glad you caught that - and brought up the ferrite beads potential water/ice problem.  I was thinking that water wouldn't bother the cores but I didn't think about trapped ice in the wintertime.  

Yes, I will seal off the top, but not sure what you are recommending for the joints. There are a lot of them.   For the fan dipole I sealed off the whole ferrite stack, top side and bottom.  I could do the same thing with the loops.... or what if I seal the top, sides and leave the gap open at the bottom where the coax just fits loosely and leave that small gap for leakage or evaporation? Or should I seal everything off using the clay/tape  treatment, etc..?

Since I took the pictures I decided to double up on all the support cords. I wanted a balanced support, so there are now four cords per feedpoint. The cords are spread out so that there is less tendency to twist too.

So please think a little about what you feel is the best approach for the ferrite cores and I will modify them...

BTW, this is Yaz 4.  I've had an English Springer Spaniel since 21 years old. They usually live to about 14 years old when things work out well. He is five.  He goes canoeing, kayaking and hiking with me. I cannot imagine life without a dog. I'm crazy about dogs.
T

On dogs: I grew up with Cockers and Beagles and have always loved dogs myself.
Our faithful ole Pug died in 2016 and we have been dogless since but I have a cat that follows me around and even licks my leg sometimes. She seems to think she is a dog, but she will not allow anyone to pet her unless it is her idea while the ole Pug loved everybody, so dogs are great companions and friends.
I remembered when you lost your last Yaz in reading on the Forum. Sad to lose an old friend, but the best cure for that had to be young Yaz. He has obviously gained the wisdom of his 4 years and is a beautiful soul if a picture does not lie. 😎


But to business:
Well, the old wisdom is to either hermetically seal (glass metal or high quality potting material) or use the “inverted bucket” technology that has been around since Ancient Egypt or before.
The bucket method allows humidity and even a splash, but air flow allows it to dry out.
In this case, you need that top (bottom of inverted bucket) to shed all the water it can and then anything that gets inside must have a way for moisture to pass through and dry out.

After the seal is made between coax and the top of the stack, it gets more complicated, because of the necessity that any heat that is generated in the beads must be dissipated so the beads stay as far below the Curie temperature as possible. For #43 ferrite that is about 300 degrees F. At that temperature the feedline will be in much worse danger than the beads though.
Since you are only using a few beads, there is some potential that sufficient common mode current losses will heat them up an unknown amount.

It might be fine if they stay cool anyway.
I sealed some of these 1020-43 beads for my class E transmitter output transformer with a product from JB Weld that I really like. It is a polyurethane sealant.
I buttered each surface with the sealant and clamped them together for 24 hours.
Some people use tape at each joint like 3M #33 or #88 tape. Shrink tube is the best to weatherproof as long as the bottom is open and as long as they are mot heating up. I like the JB weld best. Amazing stuff that is really hard and the bond is amazing.
By the way, I ran a 1/2 rod through the beads to keep glue in tue seams. You can wrap a 1/2 wooden dowel with teflon tape or I have just used nylon tubing because it does not bond well to it.
EDIT LATER: I suspect that the JB Weld will be good in the weather and you can leave the beads out where they can radiate heat. MB


Another Idea:🤓 (EDIT LATER) There are a ton of wireless meat thermometers that seem to work on Bluetooth and some can interface with your phone. The thing that cannot be certain is whether the advertised range and accuracy is there, but it is still a compelling idea. MB

If you wanted to test for heating in real time,
Here is a possible device to get data on the heating effects within encapsulation.
It is a wireless thermometer that reads up to 200 degrees F and has an RF link that is claimed to reach 1/4 mile.
Cheap too! 😎 It might not work ,but worth a try to be able to remotely test the bead chokes with hundreds of watts on the line(s)
I have been thinking of getting one of these for my toroid baluns that are going in NEMA boxes that will have vents that will not allow water imside, but will have screens to allow moisture not to accumulate inside. Jim Brown says not to put them in a box, but it is eotjer that or pot them up because I hate water damage and have seen a lifetimes worth already…😉
73, Mike

https://www.amazon.com/dp/B08Z3XH313/ref=sspa_dk_detail_1?psc=1&pd_rd_i=B08Z3XH313&pd_rd_w=veibJ&content-id=amzn1.sym.3481f441-61ac-4028-9c1a-7f9ce8ec50c5&pf_rd_p=3481f441-61ac-4028-9c1a-7f9ce8ec50c5&pf_rd_r=76A6932TECQF5ZYR2BNX&pd_rd_wg=3pgln&pd_rd_r=44a7e94a-7e6f-4616-8e36-7e7ed093dc2c&s=home-garden&smid=A2E6L4XU587CP3&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzOVFXMzk3RzVKQ1I0JmVuY3J5cHRlZElkPUEwNjQ2OTU2MlBTMzdHQVZQMEkwVSZlbmNyeXB0ZWRBZElkPUEwMDQ3MjE5MUZZWlFOUU01VjlHTCZ3aWRnZXROYW1lPXNwX2RldGFpbF90aGVtYXRpYyZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

https://www.amazon.com/J-B-Weld-Plastic-Bonder-Syringe/dp/B0B5VJZ5XW/ref=sr_1_2_sspa?crid=18MKOMG7OGF79&keywords=jb+weld&qid=1658717388&sprefix=JB%2Caps%2C92&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzN05UNEFDVlpLS045JmVuY3J5cHRlZElkPUEwMTE4MDk2WVA4MFAzQlUySTlIJmVuY3J5cHRlZEFkSWQ9QTAxMzU4NDEyUlZNQjZUN1I3MktYJndpZGdldE5hbWU9c3BfYXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Thanks for the great ideas and information, Mike!

I took it all into consideration and just finished up the mods.  I will take the simplest approach and Scotch 33 tape up all the bead joints.  I quad weatherproofed the top hole of the stacks.  I left the bottom hole open for ventilation.  I don't expect a lot of heat from the cores, so will take a chance on that.  The feedlines come straight down over 1/2 wavelength to the ground level, (at least 120' straight down) so that should keep the outer shield currents to a minimum in the first place. No ice can get in now either.

Another good thing is most of the DXing on 75M is done in the cooler/coldest months, so those cores will be starting at 30F or lower.  Or, I'll just have to talk fast and to the point like a corntester...

If these cores get ruined by a lightning strike, I'll climb up there with a hammer and smash them all and replace with clamp-ons to make it easier next time... ;D

FB on your Pug.  They are what we make them - a reflection of us.  Each dog has his own personality and each is different.  Though, I have learned the habits of Springer Spaniels very well.  I can sense when there is a problem while the Vet may think nothing of it.   I've always thought that at 5 years old, a dog becomes the perfect dog. You learn all of their habits and he learns yours. Younger than 5 years old and they can be unruly.  As they get even older, they really mellow out. Their whole life is dedicated to communicating with you. Nothing like an old dog...

Thanks for sticking with me thru this thread and getting most of the problems ironed out.  My usual mode is to do something and then later find out I screwed up a few points and have to redo.  Many times I will hear, "No, no you should have...."   At least this thread has saved me from a lot of those so far...      Frank/ WA1GFZ has been giving me some good tips via email too.
Many of these specific answers cannot be found anywhere.

It looks like T-storms, so more work will have to wait.  At least the feedlines are out there well waterproofed.


Thanks again.

T

BTW, I was thinking about feeding/ phasing... If the two loops were fed in phase, (0 degrees, equal length coaxes) it will produce a bi-directional pattern, but just like the fan dipoles, the bandwidth should really broaden out.  Phased 0,180, the bi-directional pattern will get narrower.  Then fed 0, 90 will give the normal uni-directional beam pattern.  

My point is that the 0,0 feed is like a low angle (average height at 140') broad banded fan to cover the whole 75M band, but bi-directional.  Used in conjunction with the fan dipole gives a local higher angle or lower angle for USA west coast with  similar horizontal patterns.  Each is a very effective antenna in its own right.

Here's two articles about a SIMPLE coax phasing method to feed two loops for a directional cardioid pattern.   It requires just two 1/4 wave 75 ohm feedlines and one 50 ohm phasing section. Add one SPST relay to switch directions, or do it manually.

https://www.qsl.net/xe1cdx/Hamdocs/40/40%20Mts%20with%20a%20Phased%20Delta%20Loop.pdf
http://www.iz5ljb.eu/_sgg/phased-inverted-delta.pdf

By good fortune, I already have two 3/4 wave feedlines attached (a multiple of 1/4 wave) and a 50 ohm RG-213 section.

In my case for 75M, it needs two 163' RG-11 feedlines and one 54.5' RG-213 phasing section. Simple.   This is called a force fed system because the power is applied directly to the elements in the proper phase.  A parasitic element uses electromagnetic coupling instead.

This will be the first unidirectional method I try.  I also want to try tuning an element as a reflector using a capacitor -   and also running both elements in phase to check bandwidth and signal strength against the fan dipoles.

To answer my own question from a few days ago, they recommend resonating each loop alone, one at a time, to make them identical.  When brought together, 1/4 wave apart, the swr will not change more than 0.1 according to their tests..

Thanks to Frank GFZ for these article links.

T


EDIT UPDATE:   I'm gonna build this:  Full control of phase and matching with just a few parts.  Just what I've been looking for. (Figure 5)  An L-network to fine tune the loops for optimum f-b (phase) and general performance matching. The only concern is how much loss does it add to the system and feedlines?      Note 10 at the link below bothers me a little...

Called a P/M  -  phase/matching unit

http://techdoc.kvindesland.no/radio/ymse1/20061117162439060.pdf

( I just need another 2000 pF, 3KV vacuum cap...)

Tom... I'm looking at the VE3CUI article from the old QST.  I expect that you may not achieve the same SWR bandwidth as he did.  Transmission line theory explains it:  He comes down with his quarter wave transformers of 75 ohm line to his combiner setup.  In your case, because you have a lot more height than he does, you are adding in an extra half wave of line just to get near terra firma. As we know, a half wave of line repeats the impedance from one end to the other.  However, a half wave is different at the CW end from what it is up by the AM phone part of the 40m band.  So the transformer will not be a perfect transformer.  The extra length runs it around the Smith chart faster at the high end than at the low end.
I don't believe the extra half wave will be a deal breaker but it's something to watch out for if SWR bandwidth is important to you. In case you had a very persnickety transmitter, an L-network right in the shack could clean up any sins.  Ordinarily it's best to match nearest the load, but the relatively small mismatch will be easy to compensate, and you won't have to take a long walk in the winter.  Unless Yaz needs to answer the call of nature anyway.
73 de Norm W1ITT

Those are interesting articles. Frank comes,through again.😎
If it is electrically what is prescribed, it could be great. I wonder if an extra break in tje phasing limes at the shack could allow small sections to be tried for optimal tuning? In other words, make it too short and then be able to put in short sections and test for match and antenna f-b, gain, match, etc? It could save aome cutting and reinstalling connectors during optimization.
It seems, from the articles- a real ionosphere cooker though,when it is going.
73, Mike

75M Delta Loops UPDATE 7-27-2022:

Mike and Norm,

FB on all.  

A lot has happened. I haven't decided on the feed system yet. I had some trouble with the loops. They resonated at 4.160 Khz.   Back in 2007 I had shortened them and used a stub to add length. I had forgotten.  Used the formula to bring them down to 3790.

Very productive.  It wasn't easy, but I climbed up there today and added on 24' to one of the loop bases. I changed a few things on the support ropes so that it hangs very nice, like a classic loop should.  The top at 190' and the bottom at 95'.  Avg height above ground now = 142'.  Perfect high angle suppression.

I connected the MFJ at the end of the 173' RG-11 coax.   The swr was  1:1 at 3790 as calculated!  It is reasonably flat from about 3.6 to 3.9.     I  went into the shack and see the same basic swr after the 200' hardline run.

On the air listening, I did a/b tests between the fan dipole and the one loop.  The locals in CT and NY drop down -20 to -30 dB at times on the loop. Low angle loop.  That loop must be at the perfect height to see that.  The few stations that are farther away this afternoon are at least equal on both antennas. I will test on some Eu DX tonight.  The loop is about 6 dB quieter for static noise. It seems to be suppressing the high angle noise.  It is below S1 on the fan, so no worry either way.

Right now the 173' RG-11 drops straight down to the ground, a 95' drop. I will change that later to provide some support on the tower legs.  Norm, I agree that the extra 1/2 wave of coax should not be a deal breaker.

So once I duplicate the second loop, it shud be a good platform to work with. Many things can be tried now. The second element should add 5 dB and make the pattern uni-directional with a good f-b.  The low angle lobe will make a huge difference when the conditions are right. The additional 24' at the base made the loop fill out and  have more area.

The second loop upgrade requires me to hang off the tower on 45 degree rails to access it. Tough game. Not looking forward to that.

A lot has transpired over the last few days with the loops.  It pays not to give up too easily.

Will keep ya updated.

T

Tom,
It sounds like you are making great progress. It will be very interesting to get signal reports on comparisons between the Fan and the phased loop array when you get in next Winter night season to Europe on 75 meters.
The low noise floor is very exciting. It will be interesting to compare the loop antenna and a beverage looking at Europe. Obviously, the loop will give stronger signals going and coming, but good S/N with gain is a great thing.
These are very interesting antennas, even as a vicarious experience, so updates are greatly desired. Thank you for sharing your progress. Looking forward to more.
I agree completely that you cannot give up if early phasing schemes give poor results. I agree that adding a half wave of rg11 will add very little loss and the increase in gain will quickly erase a couple of tenths of feedline loss.
You must know that getting one loop going is just an opportunity to start from when you add the second loop. Phasing probably will be critical to optimize the polar plot and radiation angle and match. It is why having the ability to insert short coaxial phasing sections can be good to quickly experiment for optimal phasing.
That 45 degree
Take your time and think three times before you make a move on that 45 degree rails hanging work.
Very exciting work, Tom.

Hi Mike,

Yes, the reduction in atmospheric noise does appear to be simple higher angle suppression.  

I have a 600' terminated Beverage aimed NE for Eu that I will compare too. It is about 600' away from the house... very quiet.  Usually in the past, on 75M, the Beverage hears about -3dB poorer than the high loops. Sometimes equal, but that is rare. It is hard to beat a high Yagi of any kind... even a full size beverage falls short... for S/N.  I have a dual diversity system modified into my FT-1000D that uses stereo headphones, one for each channel.  That is some system... (loops and Beverage combined) and gives the brain a binocular effect to work with.  It is still GIGO.  The antennas must work really well individually to work well together.

Last night I tried the loop  A/B thruout the evening against the fan dipoles.  The fan is actually a good DX antenna. (at ~100' avg)    Into EU, the fan was equal to the single loop most of the evening until about 9PM.  Then the loop slowly took over and at 11:20PM  the loop was about 5 dB louder than the fan. The loop's extra height (~142' avg) won over. I figure with the second loop it will be close to 10 dB louder  like in the past.

There is a strong telemetry signal from Eu on 3806 and 3823 I use as a beacon.

I think the 75M angles are higher early in the eve and then drop down late.  It used to be the opposite at the solar minimum IIRC.

From CT, I noticed the W8s and W9s were about 5 dB louder on the loop all night.  I was listening to locals Chuck and Bob/KBW on 3885 at about 7PM..  Chuck almost dropped into the noise on the loop with his high 2-half waves in phase.  Bob dropped -30 dB on the loop but was +50 dB over on the fan dipoles. More evidence we want to see.

And here's a first:  Today at about 11:30AM, daytime absorption conditions, on the the LOOP the LOCALS were consistently 10-15 dB!  LOUDER than on the fan dipoles.  The best path appears to be lower angles in the late morning/afternoon. During high absorption, the low angles are making it thru better.  In contrast, as we have seen, at night the loop is sometimes -30 dB weaker on locals.  

So again, I think all of this evidence points to a good combination of basic antenna potential to arrive at both a great local  and DX system for 75M. To see this much difference with these antennas shows they are well isolated and taking advantage of widely separate angles.  The real testing will be if and when I can get the loops working together. Adding another element (reflector or driven) seems to make an antenna really come to life.

I'll keep you updated as I test more.

T

Very interesting, Tom.
I am a little jealous of your very quiet QTH. I am surprised that your Fan is so quiet, but at near 100 feet, it is up close to a half wave so it is above a lot of near field trash, I suppose. I would have given that 600ft Beverage the edge, but given your excellent local noise floor there, it apparently is not like some of us with lower towers and huge RFI garbage buzzing away from power limes and electronic devices…
That diversity system is a great idea.
The across the pond favoring the fan and then the loop is also interesting. You you suspect multihops early and then fewer hops later as the ionization cools a bit and absorption at lower angles drops or maybe you are skipping over the target area? I need to bone up on propagation. I need to keep reminding myself that Britain and the Norse countries are only 3000 miles over the great circle route from you.
It will be really interesting when you get the second loop phased and drop your take off angle even more. Kind of like the old traditional snow goggles with horizontal slits, that more narrow pattern should eliminate even more noise.
Thanks for the update. 73, Mike

UPDATE:  8-1-2022:

Mike and all,

Some good progress on the 75M loops...   The hot and windy weather kept me from climbing for a week or so. The propane torch would not stay lit for soldering. There was hot solder dripping on my leg a few times.

For a few weeks one loop was always the same strength as the reference fan dipoles.  But the last two days I climbed and finished up the basic loop installation.  Now have some feedline dress work to finish up climbing and can then work on the ground for a while.

There's  now two 173' RG-11 coaxial feedlines at ground level with each individual loop resonant on 3790.  I decided to drive one loop and tune the other with a tuning cap to see if there is any forward gain or front to back. (as a parasitic reflector beaning NE, Europe)   I roughly tuned the reflector using a beacon only about 100 yards behind the reflector, looking for a sharp null.  Adding the second loop into the system moved the resonant frequency down from 3790 to 3770. (mutual coupling)

On the FT-1000D I tuned in the 3806 European telemetry station.  FINALLY I was seeing the loops take out the fan dipoles at sunset. They were always dead even before.   I thought it was conditions before, but now I know it was antenna performance.  As the night progressed, the loops were one S unit louder, then two S units and finally on a band peak, (between 11:30 -12 midnight EST)  the loop's peaks were 2 1/2 S units (~15 dB) louder than the fan dipoles! Much depends on conditions.   The loops finally came to life. All that suppressed energy finally showed itself.

Maybe the problem a few weeks ago was either the openwire line causing stray coupling, poor pattern -  and possibly the physical layout of the loops were not very good.  I cut some small trees and weeds so that I can now pull the loops out straight so they align better with each other and the boom.  I will clean it up some more tomorrow to make the layout near textbook perfect..

The local stations before sunset  had huge fades on the loops, sometimes from S9+30 over on the fan dipoles down to S6 on the loops. The high angle suppression is greater than it was before now that the loops are roughly tuned.

Some Puerto Rican stations were barely copy-able off the back, but loud on the fan dipoles.   It's interesting that the fan dipoles are at 100'  and the loops start at 100' and go up to 190'.  They displace different areas and their performance shows it.   Next will try switching the loops NE/SW with the parasitic method. It is working so well I may not bother with the direct driven feeding method and its particular problems.  But I'm always curious and may experiment with the  90 degree phasing section to see how it compares.

BTW, the noise is now even less than before. The loop's background noise, day or night is about 8 dB less than the fan dipoles.  Tuning the reflector to eliminate the noise off the back and suppressing the high angle noise really made a difference.  I can hear better on the loops if only because the noise is less. The signals may be the same strength, but the lower noise makes a huge difference in readability.  I remember that being a nice feature of these loops back in 2010. Glad it is working again.

All in all, I'm very pleased with the loop's overall performance. Was getting a little concerned why I could not beat the fan dipoles. Was thinking the dipoles might be good enough for Eu, but now see that the loops can crush the fan dipoles like a bug, caw mawn.

T

Tom,
Great report on the progress you are making.
All us Monday morning quarterbacks knew all a long that the loops are better! 😉😂😉
Tom, seriously- so many factors can skew results that the fact that the fan seemed better did not mean much, except maybe the second loop was needed, that phasing was off, that some weird ionosperic absorption was causing certain takeoff angles to be attenuated more, to…… whatever.
 The great F-B tells me that you have the phase shift right on and add the huge difference in signal in night conditions and it begins to justify and encourage your massive efforts to put up this huge array.
Antennas make so much difference because it not inly makes you louder, but it increases not only signal strength on receive, but also filters the noise floor by limiting the exposure by only looking at where you need to look for the signal.
My wife and I were talking about seeing something at distance and how you can read a sign further away by looking through a small aperture made with the hand so that only light coming from the object you wish to see while filtering out the glare caused by scattered light that prevents your retina from seeing the image clearly.
We expend so much effort on powerful amps and sophisticated receivers with low noise preamps, but so much more can be achieved if we can make big improvements in antenna performance, or even small measurable improvements.
This is very interesting and inspiring to see you make this sophisticated phased array really improve your ability to both hear and be heard on long hauls in a place in the cycle where most of us are hunkering down for 5 years.
Thanks, as always for the update.
What is the next step? It rally seems to be working very well. 73, Mike

Mike,

You made some great points;

"Antennas make so much difference because it not inly makes you louder, but it increases not only signal strength on receive, but also filters the noise floor by limiting the exposure by only looking at where you need to look for the signal."  [MB]

This is so true.  Just like a unidirectional antenna, like a Yagi, can eliminate a whole hemisphere of noise by using a big front to back.  But we need to know what we are optimizing for, horizontal, vertical or both. Stacking antennas can selectively do more of the same  in the vertical plane.

One thing that is very important to antenna testing and evaluation is having a REFERENCE antenna. A simple dipole fed with coax at 1/2 to 1 wavelength high  (or whatever can be erected on the lower bands) is so important. Without the fan dipoles as a reference I never would have known that the single loop was performing normally and that it was performing normally when the reflector was added to the loops. I never would have known that I had a 4 dB intermittent connection on my previous dipole and to replace it.  I never would have known the front to back either.  If I go on to put up a new 20M pair of staked lazy H's, you can be sure the first antenna that goes up will be a 20M dipole at 30 - 65' fed with coax. It's a great way to really evaluate and improve on a complex antenna.

Another technique is to become familiar with the various signals and stations on the band to be able to check for f-b in the real world. When I hear weak, watery signals with a lot of fade off the back, I know I am close to the sweet spot of f-b optimization.  You can also see the band edges where the f-b starts to fade.

On 40M my reference antennas are a dipole at 45' and a dipole at 100' high.  They are vastly different antennas. They told me I had problems with the 40M triple stack and fixed it. The broken stack was the same strength as the references into Eu. But now the stack is louder by at least 2  units on good nights.  Coax contamination is another problem that can creep up and a reference antenna can show this over time, if you keep notes. Of course band conditions change over the solar cycle, so it can be tricky.


There's noting like a well performing array, but it takes a lot of time and work to get there.  I get a lot of enjoyment just switching bands and trying the antennas against their references to see how conditions are and to insure the antennas are still working right.

Something I noticed yesterday.... time seems to speed up when tower climbing. Yesterday I went out and started the climb at  10:30AM and finished, and came down.  I went inside thinking I had been out for about an hour. I was amazed to see it was almost 2PM and I had been climbing for 3 1/2 hours. I was sore, but never saw the time go by so fast. Like working in a black hole as the outside world speeds up.

I'll keep you updated as I build and test a switching system for NE/ Eu and SW / USA for the loops.  I'll also post a few pics of the loop's improved physical layout alignment and independent feedline support when completed.

T


**Just for reference, here is a pic of the 75M loops at 190' high last month using openwire. The physical alignment is decent but not perfect.  The 40M reference dipole at 100' is directly under it.

Tom,
I have developed products for 46 years and I can tell you that you understand the process very well.
Standards and changing one independent variable at a time are crucial if you want real progress. Shortcuts seem easy, but there are a ton of unproductive bypaths snd pits there.
You are building a knowledge that will be very valuable to others. You know that you are not done and that is also crucial.
This is very exciting work.

By the way, the disappearance of the sense of time is called “Flow state”.
Google it. Every significant inventor and master of almost any art or discipline lives in it.
I have experienced it since I was a teenager.
Many think it weird when you talk about it though…. The cool people love ADHD better with lots of Twitter posts …😉😂😂😂

Hi Mike -

Ahhh, the flow state. I have read a few books on it and studied it closely in regards to day trading.  Really good traders do indeed enter this state and become one with the market or whatever skill they need. Intuition plays a big role too. Just like a doctor who has years of experience, he can just feel the solution.

Other than high speed CW, I've never thought of the flow state related to ham radio, however. It must be the same thing, why not? In my case I was focusing intently on the tower work to make the fear go away. I pretend I am in the shack working on a project and the fear of heights gets under control. It works for me because after a few hours the project is completed and I'm climbing down -  and   not fearful anymore. It's the anticipation that's the killer...it's sometimes harder to saddle up the horse and put on the harness than anything else.

I did some ground clearing today and positioned the loops close to perfect alignment with each other and the boom direction. The coax feed point swings on a 40' rope off the tower to distribute the weigh better.  I tuned in the 3806 Euro beacon tonight and see conditions are pretty hot. The loops are working better than even last night.  I may switch directions to the SW with clip leads and see how it does. Since everything has been matched, it should work just as well to the SW using the same parameters.

T

Notice the symmetrical flow of the repositioned loops.  (#10 THHS stranded copper)

Pic #1 and #2 show the new RG-11 coax and feedpoints at the 100' level. They will be supported on the tower legs from 70' and down.  The small 'T's   are the feedpoint PVC center insulator and the string of ferrite beads. The coax is supported by a Chinese fingergrip pipe hitch knot to better distribute stress across the coax.  I've seen the the finger grip used by commercial installers.

Mixed into the picture frames are wires from the fan dipoles and the two 40M dipoles.  The fan dipoles are end to end with the loops, no overlapping. This should maintain good isolation on 75M. They act well isolated on receive often with opposite signal strength.

Pic #3, cleared by hand to give loop anchoring guys the correct position.  The boom length gives about 45' spacing IIRC.     Also repositioned the two 40M dipoles to make the legs perpendicular/ square.

Pic #2 is looking thru guy wires from the Rohn 45 150'er. 

One of the best and most reliable beacons out of Europe was Jan OK3BJJ.  He had a high dipole atop a multistory Eastern Bloc typical large apartment building and he was on the air most every night.  I once went 16 months of working Jan at least once a month, and usually multiple times, even in summer.  The trouble was that he had a high local noise level and could transmit much better than he could hear. Many called, thinking that the propagation ought to be reciprocal.  You had to have a decent signal to overcome the noise and work him and those who didn't make the grade heard "Veak signal. Negatif, negatif." and then he'd go back to CQing.  OK2RZ told me that Jan had died a year or so back.  I miss him.
73 de Norm W1ITT

Nice pictures, Tom. That is an impressive wad of wire up there! 😎
Nice to know that fine tuning the geometries is giving you measurable improvements.

Back to Flow States for a minute. The actual thing that we call Flow State is natural and present in every inventor, artist, great musician, athlete or anyone else who has achieved a level of excellence that sets them apart from all other men. This is not to say that you must be Tesla, or Shakespeare, or Leonardo DaVinci or Mozart or Steph Curry or any other individual that has set himself apart to experience Flow. I have experienced it all my life and I do not compare myself to these great individuals. Mihaly Csikszentmihalyi from Hungary first published about it and I first read about it when I read Daniel Pink’s book, DRIVE. I applied it immediately in my management style, though I had instinctively done much of it before.
Then I attended the Commencement of my youngest Daughter when she graduated from college and Jeffrey Brown, an alumnus at the school spoke about research he had done and his book called The Winners Brain. Brown interviewed hundreds of persons who were at the top of their occupation in sports, music, business, engineering, and many other fields  and he found a common thread. Every one of these individuals had reached the very pinnacle of success in their fields, but they never ever saw themselves as “arrived”, but as being on a journey. The focus was on  making measurable improvements in their performance every single day. No home runs- just a measurable incremental improvement. Every single one of them spent hours improving themselves every day. They described a state if mind where time disappeared and their focus was total and complete and it was always positive.
The fact is that almost everybody experiences flow in some activity and whatever It is, they describe it as fun and rewarding in itself.
It is why you put yourself up there straining and sweating high above the ground for hours and not only do you not want to be paid, but you pay to get to do it.
It is addictive and great fun.
I tell my grand children to choose a career not for how much they can get,paid, though getting paid well is a great thing, but choose to do a thing that you cannot help yourself from doing and be the very best at it that you can and you will also get financially rewarded and never “work” a day in your life, though it will take all your energy and passion to do it better every single day. I deeply admire tue great basketball coach John Wooden. John won 10 national championships at UCLA and he always told his players that it is essential that you “Make every day your Masterpiece”.  Yesterday’s achievements are not good enough and tomorrow will bring more challenges. That is why you are not satisfied with that great Broadband dipole and press on to greater performance for the pure joy of it.
That is what makes me continue to improve my musical instruments when many say they are the best in the world.
We will never get done, Tom and that is a great and exciting thing. I would not have it any other way…😁😎 MB

Norm:

This should bring back memories.  OK3BJJ was a regular.  Worked him many times. Your impression is right on... ;D.
 https://www.youtube.com/watch?v=v3wTDL76Q_w


Mike: FB on the flow state.  Yes, it is a real thing and some use it very well.  Your comments are right on.

Speaking of smarts, it amazes me how some of the guys here can answer virtually any technical question.  Many have spent their lives focused on electronics professionally and as a hobby. I have consulted with quite a few over the years and you can always count on getting the right answer.  Guys like W8KHK, WA1GFZ, K1KW, K9MB, W1ITT and others are my "goto" guys.  These elite hams always surprise me with their depth of understanding.

Speaking of projects, today I climbed and dressed up the feedlines for the 75M loops..  They are supported by rope pipe hitches all the way down and do not touch the tower.   I electrically reversed the loops' direction to SW and now hear the VE1's piss weak off the back and the W4s louder on the loops than the fan dipole. Because everything is matched and balanced, I didn't have to change the  40 pF tuning capacitor that tunes the reflector!  Right now the VE1s are S1 off the back and S9 on the fan dipole.  That antenna wants to play!  I can't wait to build up the remote relays that will change directions.  That's when I can really fine tune the tuning cap for best F-B.  Having two directions really tells the story.  I'm still seeing the locals down 20-30 dB, piss weak like I expect on the loops.  I'm hoping the coiled RG-11 or closer proximity to the tower did not hurt performance.  I am still baffled why the open wire and antenna tuner did not work well, so am sensitive to watching for changes.

Looking forward to see how far down the 3806 beacon is down off the back. Later on, a remote controlled tuning cap may be a good idea to give maximum f-b across the band.

Question:  I have an extra 60' of RG-11 left over on each loop. I coiled it up in a hank for now and hung it on a pvc pipe at ground level.  This is also a 1/2 wave point so I added 5 ferrite cores there, next to the coiled cable.  I realize that the coiled hank of coax may have problems with inter coupling, etc.  How should I route this extra cable?  Should I pick up two 5-gallon plastic pails and wind  the RG-11 excess on each in an orderly fashion to improve the CM?  Or should I keep the coax straight.. or make a BIG 3' coiled hank?   I'm thinking that it could add a small amount of CM rejection.

T

Tom..Knowing what to do with that 60 feet of "excess" coax calls for measurements.  I can't recall if you said you have one of those MFJ clamp-on RF current probes, but you can make one cheap if you don't.  Fire some RF into the system, set the sensitivity for "some" deflection on the meter and walk along the line (perhaps set up on saw horses} and look for a periodic variation that would match 80 meters.  You have about a quarter wave of real estate to look at so you should find something if there is enough common mode to worry about. Or it might be flat.  ( I believe the habit of calling a low SWR line "flat" comes from the old days when fellows would run RF ammeters shunted along their open wire lines, or neon bulbs in the case of the less financially fortified, to test the match.)  At least in this iteration you are walking along the ground, not hanging on a lanyard.  The spirits of the buzzards of old will be walking with you.
73 de Norm W1ITT

Tom,
My experience with full wave Delta arrays phased with coax cable is close to zero.
However, I have a couple of fake Socratic questions so I avoid making a complete ass of myself by asserting something wrong:

It seems to me that you have different impedance loops on the differential and common mode feedline lengths.
The differential path is the one that you are tuning for the necessary 90 degree phase shift to get the unidirectional cardioid polar plot you want, is that right?
Seems like that is an odd number of quarterwaves electricallly, allowing for the rg11 velocity factor of 80%?

However, the common mode resonator is a 100% velocity factor because it is in the air- or close to that.

So, of you have an effective common mode choke at the top, why does it matter if the feedline touches the tower or gets close to it? That is a real question-by the way- not a Socratic mind game.

Also, if you have a decent choke at the top, a coil close to 125 feet from the top- 1/2 wavelength in air can only increase the choking impedance and not affect the differential path phasing , so why not?

I do not have answers on this, but those things make me want to ask what might,be stupid questions about these matters.
Norm and Chuck may have direct experience here…

One thing seems clear to me- the use of the rg11 must be isolating the differential path very effectively, given the high  F-B and the lack of need to retune when you switch in your phasing line to reverse.
You are obviously wearing blinders for the locals, exactly what you need to keep RFI and qrm from interfereing with your DX paths.

Norm,

OK on the common mode test.   I will look into it and let you know what I find.  Tnx!


[Mike we posted at the same time - see below...]  

Now for another question... I am stuck and cannot proceed with the relay switching and parasitic reflector f-b tuning until this next calculation is done.

Normally to tune a stub for a PARASITIC reflector, I would put a capacitor or inductor across the reflector stub/feedline and try it. If neither worked, I would cut some feedline off and try again until I had a cap or inductor that cleanly covered the range and provided a sharp null of front to back.  I am presently getting a null, but it is very broad... no sharp dip -  and seems far to the edge of the tuning range to be effective.  I think I need to cut some feedline and try again. I would like to stay with a cap if possible. Not sure.

I understand that a 1/4 wave reflects back the opposite value. IE a cap becomes inductive. And, 1/2 wave reflects back the same value, IE a cap is still a cap.

In my case now, randomly cutting the feedline will make a major hardship because of the difficulty of putting on new connectors for RG-11.  I want to calculate the length of the stub, determine the approximate cap or inductor value, THEN cut the feedline.  So far I have some numbers but am not sure before cutting anything.

RG-11 is 0.84 velocity factor.   1/2 wave = 109'.    1/4 wave is 54.5'.     The present feedline length = 176.3' for each loop.   162.5' = 3/4 wave  - it is presently 13.8' longer than 1/4 wave.  This makes it inductive and a cap should work, right?   Each loop was resonated to 3.790 MHz as measured at its feedpoint on the tower, no feedline attached.   Each feedline was measured alone and the low impedance freq was found to resonate at 3.517 MHz using the MFJ meter.

The loops perform decently with NO reflector termination, an open, on the end of the 176.3' stub.  This tells me it is too close to the range border. I see little difference when I tune a 100 pF variable cap or inductor.    What is the proper feedline length to resonate the reflector to about 3.725 Mhz when using a variable cap of 30 - 300 pF?  I have a vacuum cap available I could use. My instinct tells me to cut some feedline, but I'd rather have a calculation guide me first.

Thanks.

T
 

Mike,

OK on all.

The loops are using a tuned parasitic reflector.  The 90 degree phasing section is out for now. Maybe later.

As for the RG-11 isolated from the tower... I figured just in case it has some CM, it may be better to let it float. It probably couples to the tower anyway, being only 1' away.
I definitely don't want the two feedlines to see each other. Maybe being overly cautious due to the openwire test failure..

The calculation I need probably uses a Smith chart, though I have figured it out on paper in the past. I have tuned a lot of Yagis and loops using stubs in the past, but I do not like the way this feedline/ stub is acting.  I am usually able to get a sharp null of -30 dB, but tuning the cap anywhere from 0 - 250 pF gives me roughly the same f-b null with this particular 176.3' feedline length.  Maybe the reflector is resonating down around 3550 when I have found it best in the past to be up around 3725 to work well on 3790.

The antenna works "OK" as is, but I think there is a better optimization for tuning in there somewhere.


I hope this is enuff info.

T

BTW, tonight, beaming SW, the Eur beacon on 3806 is down -15 dB off the back. That f-b is "OK" but not quite what I have seen in the past with this array.  The W4s are definitely louder on the loops SW, [vs: fan dipole] which is a good thing.

Tom,
Again- my experience is nil on this, but a couple of observations:

1- if you put a capacitor across a small loop, the capacitor will be a very high impedance at resonance, so the capacitor is very critical in value to reach resonance.
Putting a 250pF cap across a resonant full loop means that it is across an impedance of  75-200 ohms depending on the geometry of the loop with 100 ohms being common.
Shunting a 250pF cap across a slightly inductively reactive resonamt loop means that it can have almost no effect at all, IMO. Now, if you were to put a capacitor in series with the feed on the loop, you would be injecting a capacitive reactance in series with the inductive reactance and that would tune the loop higher or lower.
However, we are talking about a very small amount of reactance here, so any capacitor will necessarily be very large to effect any change as a series tuning element, IMO.
I am speaking out of general,experience, not specific knowledge here-again…

2- I watched a YouTube video about 2 element yagi modeling and ot includes plots of the frequency vs gain,and F-B functions and it is interesting to see that there is a sharp inflection point in the gain and F-B curves aroumf resonance as a parasitic elemet passes from resonant up t0 be a,director and down to be a reflector.
Above that inflection point, there is a small broad peak,and,then the curve trails off at a low slope function.
This tells me that the tuning of reflectors an directirs are only,very critical,just above and below resonance and then they do not cha ge much for wide frequency shifts.
The thing that is more critical is the match, however and that should be adjusted for maximum power transfer efficiency.
See the screen shot of one of his graphs and the limk to themYoutube video,below:
73, Mike


https://youtu.be/2DcvmGPLdT0

Hi Mike -

Thanks again for the info.  Yes, a parasitic element will greatly influence the driven element (swr) when its resonant frequency approaches the driven ele. I know where the parasitic element is tuned when the swr soars. In the case of the loops the reflector is down around 3650.  I'd like to pull that up somewhat by trimming the RG-11 stub coax soon.

Did some more testing today.  Got the force feed system [90 degree phase shift section] to work pretty well, but not as good as the parasitically tuned reflector.  So back to the tuned reflector.

The open 176' stub RG-11 feedline is pretty well optimized just as it was cut, by sheer coincidence.  To verify, I added a few feet to it as well as larger sections and the f-b just got poorer. I am convinced that by shaving OFF a few feet of RG-11 it will find the sweet spot of max f-b.

I checked both directions on the band tonight and can see times when there is 20-30 dB f-b both ways.  I think it's time to cut/trim the coax and go for the -30 to -35 dB null.

The reflector tuning seems broader, much broader than the open wire version. The original question, the subject of this thread, was about bandwidth of open wire vs: coax.  The tuner was very hi-Q thus I was never satisfied until I found a sharp dip with the coax. But it's just not there.  I tried adding a bunch of random lengths today with caps and inductors, but there was no super sharp f-b null, just a broad area.  That's OK, cuz I see decent f-b performance from about 3600 up to 3900. Maybe the extra coax loss is causing it.  But the loops are 2-3 S units louder at times than the fan dipole into Eu, so WTF.

So I  designed up a simple relay switching system for NE/SW.  Ordered the relay on eBay, $13.  It's just one DPDT 25A  open frame Potter/Brumfield relay.  The stubs have no coax or L/C components to switch around... just an open stub of the proper length and the driven element.

I'm pretty happy with the present performance and feel like a few fine tuning cuts of the RG-11 will be all that's needed to finish up.  

Early tonight there were a few W3 nets on that I tested with.  Usually they are too close to see much difference, but tonight the W3s were much louder on the loops.  The VE1s were pissweak off the back and loud on the front.  I heard a few Euro hams talking locally come up out of the noise tonight at sunset. It was quite dramatic to hear on the loops - then they dropped down again into the noise minutes later. And the old trusty 3806 Eu beacon was louder than the fan and weaker than the fan in the correct directions.  This is now a few nights of repeatable results.  75M is not an easy band to get decent gain.  F-B is easy - even a loopstick has directivity. But meaningful gain over a high reference dipole is a bitch at times.

When the relays arrive I'll have some more updates.  Switching directions really adds data cuz there is gain in both directions now. Before it was the fan against the loops. Now it will be the added gain of another direction to make it more dramatic.

I'm still seeing a ~6 dB better S/N in favor of the loops. The noise is simply lower. This is not T-storm noise, but ambient background noise.  Not sure why, but the difference is there day or night.  Huge advantage in hearing the weak ones.

T

75M Delta Loops UPDATE:  8-6-2022

Hi Mike and all,

I've got some very interesting test results.  Using the tuned reflector technique with an RG-11 coaxial stub. SPST relay for directional switching.

Band conditions certainly have a big effect on the f-b and gain of the delta loops.  Tonight between 4PM and 7PM I saw the best performance so far.  I was listening to 3760 - to a group of VE1s to the NE, about 500 miles away. This is in the same direction as Europe for me.  They were running a net so I had a large sample of stations.  When listening to the NE, there were several stations that were S9 +20 over.  Most were below S9, but all easy copy.   When I switched to the SW off the back, I could not copy any of them!  They dropped into the noise as much as -30 to -45 dB.  I've not seen that deep of a null off the back of this antenna before.  It just took the perfect conditions to show itself.

Now here's the kicker:  There was a group of W4s to the SW centered in Tennessee on the same frequency having a QSO.  Neither group could hear each other. When I listened to the SW, I could hear the W4s S9 +10.   The VE1s  were gone.   When I switched to the NE, the W4s were gone and the VE1s were strong again as before.   This is the ultimate set of rare test conditions - to have two QSOs on the same freq and being able to hear either one clearly - by selecting directions.

I've not tried to trim/ fine tune  the RG-11 stubs feedlines yet. But I would like to raise the sweet spot from 3760 up to around 3800. I notice that the f-b tuning is rather broad, so I think I can get good performance up on 3885 too.  I'm hoping that a trim of about 1' to 2' per leg oughta do it.  

Over the last few nights I've heard a few foreign hams from Europe on 3795 calling CQ with no response. The loops appear to do their job when switching on them.  DX activity on 75M has been dead due to the summer and static. I hope to change that soon... :-)

I've not done any field strength coax measurements yet, but to see deep f-b nulls like this must mean the common mode stray radiation is very low.  The loops always beat the fan dipole when over 300 miles away in the proper direction. Locally, (<100 miles)  the fan dipole is usually about 20 dB louder than the loops. I can usually tell where a signal is from, distance and direction -  in a few seconds. The delta loops have good SWR bandwidth as well as performance bandwidth, so I'm pretty happy with the system so far.

T

Tom,
I expected the side F-B performance from the graphs I posted last week and that is a great thing.
You have excellent performance on both antennas IMO.

I think that you need to look at all the mechanical design
To see if any improvements can be made and the common mode choke(s). The chokes are the weakest part of your system , IMO, though I am an overkill fruitcake so maybe ignore me…🤪😉😂
Good work. Please, keep posting on sir data.
I have learned a lot from it already.. 73, Mike

FB, Mike -

Let's see, mechanical design of the chokes...  How would you improve them?     I sealed them off for water / ice as suggested.  They are supported with rope by the center insulator taking the strain off the coax.  Do you mean the potential lightning pulse problem?


The thing I am concerned about is an ice storm putting a heavy load on the RG-11.  I have no problem with RG-213, but RG-11 is pretty light stuff.  If I had to bet, I would say everything should be OK. The movement will be minimal since supported by towers.

Interesting 75M conditions lately. A few days ago conditions and f-b tests were normal.  Yesterday they peaked and gave outstanding performance. But tonight the loops are about the same strength as the fan dipole and the f-b is less than yesterday.   So tests need to be averaged out for changing conditions.

Tomorrow I will bite the bullet and cut the RG-11 stubs shorter to pull the loops up in freq..  Frank gave a good suggestion to add a relay to switch back in the cut stub - to allow the sweet spot on 3770 to remain as well as covering 3885.  I may do that to broaden the performance range.

I'm trying to find the best place to put up a 20M array. It could be real aluminum Yagis or a wire array of Lazy H's with reflectors.  Everything I've considered has issues with interaction, span distance, wrong direction, weight, etc.  

T

Tom,
I should have said :
1- Mechanical issues
2- Common Mode choke design

Mechanical-
You already have recognized these challenges and have addressed some of them.
Your sealing system looks very good and leaks are unlikely if you have eliminated internal gaps to prevent anything from “breathing”.
Even small amounts of air moving in and out of an enclosed space will inhale wet air but never exhale all the moisture so it accumulates.

I am uneasy about the RG-11 hanging unsupported.
True-it is light and the skin is tough, but take a trained gymnast and let him hang from the bar for 10 minutes and he will not notice it, raise that to an hour and he rises to the occasion. Make that a week uninterrupted and he goes down.
Like any antenna we put up on a calm sunny day, it looks like it can go on forever, but the it rains and then the rain freezes and the light coax can weigh 75-109 lbs or more and then the strength becomes critical.
This SAT and CATv stuff has low density foam, 50% per- week braid and worse- an aluminum inner shield that bears nothing and will not stretch much.
Ok- the stuff does stretch you get Chinese handcuff action in the braid snd the foil fractures so it is no longer continuous, perhaps.
Can you depend on the feedline to keep the same performance?
That is an empirical question and the experiment will answer it.
As an obsessive over designer, I am impatient to get past the failures and destruction by avoiding all recognizable and preventable failure modes and suffer the jibes and guffaws of my neighbors who consider me an obsessive fruitcake…😉

I have considered it a the easiest thin is to attach a 1/4 inch Dacron braided line to each hanging rg-11 feedline and add knitted a knotted small loop half way down and then tie the top to your 3/8 Dacron line and two 1/4 lines upward to each supporting tower at the half way point as supplemental support and dampers to prevent wagging in the middle.
The downside is that it will be more likely to accumulate more ice, but 1/4 Dacron is good for about 900-1000 lbs, so as long as the top snd middle supports hood, you are good.

Or you could ignore this old obsessive compulsive freak and finish the experiment this winter…😉😂😂😂

Finally- I am still uncomfortable with your California KW cooking you bead skewers at an inconvenient moment..
Of course the most inconvenient moment may be that February I’ve storm snd I’ve is s great cooling substance, so probably not an issue.
73, Mike

Mike,

I appreciate the suggestions.

The RG-11 is supported at the feed point at 100' and again at 60' using the Chinese finger grip pipe hitch rope knots.  So there is presently two hanging feeders with 60' and 40' unsupported drops.   When it cools down later in the week I'll climb up there and tape all the unsupported legs to the tower rails.  I'll tape them at 5' intervals.  That should make a big difference in support and also keep the swinging-in-the-wind at bay.   I kinda knew I would eventually have to do this, but wanted to take it a step at a time.

Good point about the internal stress that's put on the foil and braid. Hopefully the light weight of the RG-11 will cancel out the stress vs: using RG-213 that is stronger but much heavier. Maybe it's a wash.

Back in 1988 I had a 120' free hanging vertical drop of RG-213 attached to a 75M dipole. It broke its internal shield braid.  Boy, was that a hard intermittent to find!  Turns out that the coax got stretched out because it was moving up and down in the wind until the braid simply broke and pulled apart at about 8' above ground level.  It was anchored to the ground with too little slack. It would fix itself for a while then rinse and repeat.  I never really found the problem until one day I finally lost patience and ripped the dipole down. It took a VOM braid end to end test to find it. IE, the last thang you wud expect...  So this sorta stuff does happen.



T

I believe that your plan to take unsupported lines to the towers every 5 feet will do it. I see no negatives at all in this and it will prevent the tortuous wind from destroying it.
Time and the elements tell a true story about our decisions in designing antennas.
You have done much to defeat Murphy…😎

Tom,
I found this article in a 1984 73 Magazine issue.
The guy built a 75 meter fan and only spread the ends 3 feet and got less than 1.6 vswr from 3760 to 4.0mHz.

Thought you might like to see the article.
My only co cern with his design is that he was using awg 18 galvanized steel electric fence wire for the antenna….😳😬😬😉😂😂.

One cannot help but wonder if part of the broadband characteristics have to do with the extra resistance of the antenna wire.
I bet that he could have achieved 1.00 swr across the entire band if he switched to nichrome wire….😉😂😂😂

Anyhow- assuming that the wire material was not the biggest factor, one might conclude that good results could be had at even smaller end spacings than the 20’ you and others have used. 73, Mike

Hi Mike,

Makes sense.  In my case, the difference between a single #12 wire and a 20' spacing effective thickness is X  a few thousand.  So the swr can make stellar improvements over a single wire like <1.5:1  from 3.5 to 4.0  - what I see here.


The difference between  20' and 2' spacing is only about X10, thus the 1.5:1  between 3.760 to 4.0.    But ANY spacing is better than a single wire. [though, in this example it does appear to be non-linear, in favor of using the widest spacing]

I would use copper wire.  

My fan dipole continues to do VERY well for both DX and local work. Best local "compromise" antenna  I have tried.


The 75M delta loops:  I buttoned everything up [project finished] and do a nightly A/B test on the 75M signals. Interesting that the DX window Euro ham stations show the biggest forward gain difference between the fan and loops  - just as I had hoped for.  Also, the loops are much quieter for background noise hiss. I'm still not sure why. It can be 6 dB most of the time and often the difference between hearing the DX or not.  The front-back is amazing on the Euros.  They go from +20 over to into the noise.  However, the f-b to the USA is about 15 dB less. Maybe it has to do with ocean to the NE and land mass to the SW.  It has always been that way over the years.


20M array:
Right now I am about to start a new thread about building up a 10 element 20M array.  I have ten  ~35' long aluminum elements sitting on the ground. They are 2" diameter at the centers, strapping.  I want to build either a 2X2X2X2 array at 35', 70', 105', 140'    OR a 3X3X3.  I'm also considering a common reflector with both a NE and SW driven element to have instant switching NE or SW.   I was listening last night to the 20M EUROS and ZL/VK stations coming in at the same time, around 10 PM.  

Also considering a pair of 4 el Yagis, hanging on gates, using ropes to manually rotate them. I have done that before, but find I am too lazy to go out and rotate them very often...

Will start a new thread in a week or so once I settle in on a design and take some beginning pics.   This has been one of the hardest decisions to make.  There are many options with so many good and bad points to work around. The work load is significant too, based on design.   I plan to tune them individually for gain, f-b and swr by raising and lowering them on a temporary halyard using a beacon and receiver, etc.

I don't plan on any 15M or 10M antennas until I see solid proof of a robust solar cycle. 20M is always a FB band, but when 10 and 15M are hopping, 20M becomes a ghost town.  I have considered a stack of eight dipoles fed with open wire for 10-20M. This would solve the problem, but the system would be bi-directional, thus compromised.  Log periodics are a solution, but mucho work too.  It all depends on the sunspots, which are really unpredictable.  Either way, there should be enough solar activity to provide SOME fun on 10-15M for a few years at worst.   Decisions, decisions.


T

Hi Tom,
On the fan dipole article above, it is different than the W4xxx antenna that you used that stagger tuned the dipoles in that the elements are equal at 110 feet total.
The K7MEM.com that presents the fat dipole from the Antenna Anthology vol 2 also has equal sides with a 3 ft spacing, so the only difference is that this 73 Magazine article has a fan shape while the fat dipole quickly goes to a 3 ft spacing.

The thing this last guy said was that he gained little more by spacing more, but the wider spaced one stagger tuned, so they are different and may have different optimum spacing when equal or unequal.

My next question, however, is- what would happen if you added a third elements half way between? Could the bandwidth be spaced even more?
I know you are on a different track right now, but it is an interesting question only answerable by empirical testing.

On the 20 meter beam, it made me think of the 6 element wire beam I built by adding reflectors and directors to an extended double Zepp wire antenna.
I wondered at that time what would happen if I could have stacked two of those arrays (8 elements)
My 80 element 2 meter antenna was actually based on 8-10 element beams designed by Russ Farnsworth. It began with an extended double zepp driven element and added a pair of reflectors, and two pairs of directors.
I used coax phasing lines fed by power dividers made from square aluminum tube with copper tube center conductors.
All you need to do is scale it up 10 times to go from 144mHz to 14mHz…😉😂😂😂

Seriously, sounds interesting. I am wondering, though, why you are not making a 5 element Delta beam?
73, MB

Tom,

This is a really long thread with lots of iterations. Can you go over your final measurements on loop lengths, spacing and anything else relevant to reproducing this antenna? Perhaps a synopsis article in the Antenna section for posterity?

Thanks,
John

Hi John,
I second that. Tom has published a lot of length, spacing and other data within the thread, but if compressed, it would make a fantastic article for others to build this excellent design. Do not forget the pics either, Tom. As a technical problem(s), I have felt that belonged here as an engineering problem to be solved.
It would, however, then clearly be an antenna article as a complete design and reside in Antennas. 73, Mike

Hi Mike, John -

Making condensed articles is a good idea, though in this case I will leave it as an "experimenter's delight." These threads [blogs at times] are more to inspire and show the various trials and tribulations of constructing an antenna system that is out of the ordinary for performance. This is also a great way of keeping archive notes for future maintenance.  I have many times gone back and referred to things I've built but had long forgotten.  

It is difficult to get more specific with plans to duplicate what I am doing, other than what I have already written. The problem is that for both the fan dipole and especially the loops,  wire lengths are greatly affected by height above ground, shape, spacing, coax velocity factor, other antennas, etc.  The best way is to start with the published formulas and expect to change  dipole/loop lengths until you get resonance on the driven loop or dipole.  Then adjust the reflector stub for each direction to give the best front to back based on real signals on the band.

Delta Loop info:  Each loop is resonant at 3790 (with no feedline).  The two RG-11 open stubs (84% velocity factor) are about 170' long each after final trimming.  Your mileage will vary.


Another thing - unless you can get the bottom of the loops to be at least 1/2 wavelength above ground, it is best to stick with dipoles. (Yagi style)   For effective loops, it would take a 190' tower on 75M and a 95'er for 40M.  So 10-20M loops would be a better way for amateurs with towers of 60' or less.   Inverted Vees will work better than low loops, though flat dipoles should always be the goal for best performance.

There should be enough info within these threads for an intermediate to advanced antenna builder to pull it off.  Or if any questions, just ask away and we will try to help. We help each other as shown by the many, many good ideas that have modified my plans over time.


BTW, 20M array Update:

I settled on a 2X2X2  array.   Three, two-element Yagis at 35', 70' and 105'.   They will be mounted on steel swing gates for manual rope rotation from the ground.  I ordered RG-213 coax, ferrite beads and 2" diameter fiberglass rods for the driven element centers. There will be a combination of coaxial choke and ferrite beads at the three feedpoints.  Now in the drilling and blasting mode.  

The 40M 2x2x2 stacked Yagi array is probably the best performing antenna I have, so why argue with success? I will duplicate it for 20M scaled down by 1/2.   The overall f-b is always greater than a single 2el Yagi due to the "curtain array" effect. My 40M 2x2x2 has a 20 to 25dB f-b.  Also the horizontal main lobe is quite broad compared to a 3el Yagi. This is an advantage when using a manual rotation system as I have.

As a reference dipole, I will add a single aluminum tubing dipole at 65' high, about 150' away from the 20M array.  Notice that 65' is about the average height (center point) of the 20M array.

T

Nice summary Tom and I get it, there is a lot of information in the give and take and experimental iterations found in the thread, so keeping it metaphorically placer mining for gold nuggets in these pages as opposed to gold jewelry ready to wear leaves a bit of fun for the next guy to “pan out”.
Also, the reason I will not build a delta loop for  75 meters is precisely because I do not have the requisite150-200 ft towers that allow the performance you are seeing.
However, I am inspired to put some of my own cache of CATV-SAT rg-11 to work for a 60’  high fat dipole or fan dipole myself. It will serve for shorter range hops and my 80’ monopole will rise next year for 160-80 meter longer range work to come.
I have been eyeing a conical monopole setup for that tower with 8-10 wires around the floating insulated 25g center support. Looking at covering 1.5-4.0mHz on that.
This is a fun thread for so many reasons, even as an armchair exercise.
So many ways to do everything!😉 73,MB

Tom...
The triple stack of 20m Yagis sounds swell.  I have a question  to axe regarding feeding the stack.  Perhaps it was covered in previous discussion of the 40m stack but it's rather voluminous to peruse at this point.
How do you combine the three Yagis and get things at 50 ohms?  Ages ago when I was building FM transmit arrays, if I had a 3-bay, I'd tune each bay to 150 ohms, j0 and combine them with a wavelength (electrical) of line between them.  As it was air dielectric coax, that gave me one lambda spacing and all was hunky dory.  The middle bay had slightly different mutual impedance to its neighbors than an end bay, but that generated just a bit of null fill in the elevation plane which we did not begrudge.
How is it done at JJ Worldwide?
73 de Norm W1ITT

Mike,

Yes, the fan dipole is really a worthwhile project.  When using it, it feels like a dummyload... :-)  I can go anywhere on the whole 75/80M band and see a great match.  75/80M is an especially large band to cover. (%-wise)  

For a DX antenna, if you have limited tower height, like say under 80', then the best antenna for 75M and possibly 40M is a pair of phased dipoles. Space them 1/4 wave and feed them 90-120 degrees out, make them switchable directions and you gots it all.    They work better than a parasitic Yagi when at low heights around 1/4 wave above ground.


Norm,

I was just thinking of how to match the three 20M Yagis...  In the past I usually tune stacked 2 el Yagis for as high an impedance as I can get away with. 75 ohms is possible for each Yagi and still have good broadband gain. When combined and fed with a 1:2 unun or just tied together and fed with 50 ohm coax usually works well. I usually experiment and find the best solution by trial and error.  Sometimes a short 75 Ohm RG-11 insert can help.

I also have a 3 way combiner from Array Solutions... 50 ohms in with three 50 ohm ports out. Gotta see if I can find that somewhere around here.

Also considering a 180 degree flip for the center Yagi which will give a nice higher angle 35 degree takeoff. The three Yagis in phase are about 13 degrees TO.

I was listening to a guy on 20M last night with a 5el Yagi at 140'.  He was having trouble hearing stations and blamed it on the low angles and sharp nulls on his high Yagi. You had commented on this earlier concerning corntest stations. I do not want to get caught with a low angle cigar pattern that works only 3% of the time at best. Especially when angles start going higher later on with active sunspots.


BTW, thinking ahead, I'm considering a fixed NE/SW 10M stacked dipole array.  Wanna hedge my solar bets.  Imagine  TWELVE 10M aluminum elements hung from 190', like venetian blinds, spaced every 16', all the way to the ground.  (190' down to 16')    Or, make the elements full wave and have a bunch of stacked lazy H's.    Each 10M element would connect to the single open wire feedline  fed starting at the bottom, that is flipped over 180 degrees at each element.  The vertical pattern would be clean with ONE lobe at <3? degrees.  The horizontal pattern would be a bi-directional  figure eight, broad like a dipole.  This would be a "listening everywhere" DX array and probably quite fun considering how crazy and unpredictable 10M can get during the hot sunspot times.  Signals coming in from many directions... the times when we burn out rotators trying to keep up with propagation.

The question I have:  Rather than calculate the feedline placement spacing on each element to get a perfect 1/2 wave  0-180-0-180.... phase relationship with cumulative errors, how would you experimentally find the proper feedline connections?   What if you stretched out the feedline horizontally 5' above the ground, terminated it at the other end and put 100 watts into it and used a florescent light or FS meter to find each perfect 1/2 wave point. Then tie on the element and go to the next position based on the brightness, etc.?  I imagine adding each element would drag the phase a little off, but not sure.  I don't want to build one of these and "hope" the calculated phasing is correct; rather have it right on the money since a small error on 10M can really add up over a twelve element run.  Maybe after doing a few element placements, the spacing distance will be the same and not require further placement effort...  

I will be using  #10 THHS insulated wire for the OWL.  I don't want to go with equal multiple OWL feedlines due to complexity and the fact that it is only for 10M, thus I can get away with the 0-180-0 flip..  

Any ideas?   I figgered you've had a lot of experience here with the many SW BC station arrays you've set up.


T

Tom...
I don't think the fluorescent light will give you the precision that you want and need for the 10 meter Venetian.  Do you have one of the NanoVNAs ?  If not, get one.  The new VNA-lite or whatever they call it has a 4" screen and goes for around $150.  They go up to 6 ghz but we HF guys don't care.  Or you can even do this for $50 with the original Nano.
What you do is connect the Nano to the feedline via a balun.  Set a marker for whatever 10 meter frequency you want to play at.  Then take a reference point by putting a shorting bar across the feedline.  A bolt or a butter knife will work.. Obviously, enameled wire complicates this.   Looking at a Smith Chart ,note the position of the marker on the perimeter of the Smith Chart.  Every trip around the chart is a half wavelength.  You can take this from there if you use a tape measure to get you into the ballpark and the VNA to get some precision.  I can't recall if the Nano can change the phase reference position like the expensive analyzers, but it doesn't matter.  Just memorize the starting point. Or start your butter knife at a point that's easy to recall (i.e. the right end of the axis of reals)  If you can enlist a helper, you can take the smart end (the VNA) or the dumb end (the butter knife) and mark the points on the line for precise placement of your dipoles.   Remember the Lecher Lines we used to read about in the old buzzard radio books?  This is in the same vein but now we have great instruments for chump change.  We can now locate half waves and multiples with great precision.
73 de Norm W1ITT

Good info, tnx Norm!

If I build it, now I know it can be precisely tuned, so would buy a NanoVNA.


Do you think by adding each element it will affect the phase placement farther down the line?  I realize that 5' off the ground is close for the elements, even at 10M, so wonder if these phase placements will get corrupted once the array is raised high and put in position.

Yes, bare copper wire will be a better choice. I still have a lot of this THHS #10 insulated from the delta loop openwire tests.

What is your opinion of this array as far as performance and usefulness as a fixed NE/SW bi-directional antenna with near horizon reach?  There is no way to switch to higher angles.   I actually have fifteen 10M elements ready to modify from an old 10M stack of the last solar cycle, so WTF.  The open wire is cheap. I plan to find the 75 ohm tap on the OWL / balun at ground level for the 75 ohm hardline run to the shack.  The only cost would be some bare copper wire for OWL.  The only drawback would be the lack of uni-directional pattern, thus more noise on RX.

T

I was just seeing if there is a cheap and dirty way to feed three yagis and here is on possibility:

You can make the feedpoints to be 50 ohms and then run a 3/4 wave phasing coaxial cable made of rg11 from the top to the middle of the array. 3/4 wavelength for this rg11 with a VF of 84% is about 41 feet. This may be close to what you need to get to the middle.
Then you do the exact same thing from the bottom yagi to the middle.
Then you put a 3/4 wavelength of rg11 from the middle yagi feedpoint to the node where all three are connected together. It will all be coiled up.
Each line will have been transformed to 100 ohms and when connected together, it will look like 33 ohms. Now, add a 1/4 wave coaxial Q section of rg11 to the feedpoint and then connect a flat 50 ohm feedline from there to the shack.
If I am not mistaken, all antennas will be fed in phase and impedance matching should be close to a flat line as long as the phasing lines are exactly the same length.

It will take 41+41+41+13.5 = 136.5 ft of rg11 and the 50 ohm feedline needed. The loss would be low even with all the phasing-transformer lines.
I may be missing something, but it seems possible.
Phase errors, of course cause grating lobes in any multi yagi array and fine tuning lengths could clean up a lobe pattern if it gets ugly, but f-b is not hurt if elements are tuned properly. 50 ohm common mode chokes can be placed right at the feedpoint. Just a thought….MB

Tom...
I can't think of any reason why adding successive elements would cause a phase drift as long as they are pretty much identical anyway.  Going back to my time building FM arrays, I think the longest bottom-fed array I built was 6 elements and we just put them on equally spaced.  In some instances I took phase and magnitude measurements at each bay and never saw any phase drift to amount to anything.
A Venetian array of the size that you are contemplating should have a few minor lobes in the elevation pattern to fill in missing angles.  If not, a separate low antenna, for high angle stuff, could be made cheap enough although it would not have the gain of the stacked monster..
I can't emphasize enough how capable the NanoVNA series of instruments are for the money.  I've made my living for decades staring at the high priced HP and R&S instruments, and own a few.  For amateur use, these Nanos are comparable to the best Alien Technology that ever came off the flying saucer.  Here's an Eham discussion snippet on the NanoVNA Lite series that seems to be the latest.  As to where to buy, I'm not sure... It's pretty fluid.
73 de Norm W1ITT

https://www.eham.net/community/smf/index.php/topic,136813.msg1269435.html#msg1269435

Forgot to do the Paste part of cut-and-paste.
N

I second Norm's suggestion. The Nano is the bees knees! Once you are finished tuning your antenna array, you will find that they are great for tuning filters and anything else RF related. Make sure you get one with the calibration board. That way you can set and save a calibration for the freq.(s) you are using. I also invested in some small cables with SO-239 connectors on. They usually use SMA's to connect to the Nano so the extra cables make it a little more unwieldy.

VNAs are impressive. Good calibration modules important and cabling to get best results, I understand. These cheap ones might not be great at 1gHz and speed snd data points limited, but for Hf, they are amazing for the price.

Edit: Sorry SLK, I seem to have posted at the same time as you. 73, Mike

Edit: For a more professional unit for about $600, this SDRKits unit has great specs and far less expensive than a $20K Lab model…

https://www.sdr-kits.net/

FB on all!

It's time to start a new thread since the 75M delta loops are finished and we are moving into the 20M 2x2x2 stack and 10M 12 el dipole stack.  I will be having some questions about these projects and the NanoVNA.

Here is the new thread:

http://amfone.net/Amforum/index.php?topic=47651.0

Thanks to all for a very informative, helpful and effective thread!



T