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Author Topic: Question regarding antenna bandwidth for coax vs: open wire line  (Read 37180 times)
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K1JJ
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« on: July 05, 2022, 03:13:18 PM »

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



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« Reply #1 on: July 05, 2022, 05:45:03 PM »

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
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K1JJ
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« Reply #2 on: July 05, 2022, 06:24:40 PM »

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
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« Reply #3 on: July 06, 2022, 09:06:57 AM »

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.
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« Reply #4 on: July 06, 2022, 02:07:53 PM »

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
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« Reply #5 on: July 06, 2022, 02:38:10 PM »

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!
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« Reply #6 on: July 06, 2022, 05:26:55 PM »

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.   Grin

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.   




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« Reply #7 on: July 06, 2022, 05:31:17 PM »

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.


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There's nothing like an old dog.
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« Reply #8 on: July 06, 2022, 07:05:24 PM »

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 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.   Grin

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  show the delta loops at 190', but are hard to see in the sunlight.  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.





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. 😉
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« Reply #9 on: July 06, 2022, 07:45:45 PM »

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
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K1JJ
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« Reply #10 on: July 06, 2022, 11:45:47 PM »

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


* RG-11.jpg (308.26 KB, 1800x1800 - viewed 197 times.)
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« Reply #11 on: July 07, 2022, 12:33:28 AM »

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…😉😁


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K1JJ
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« Reply #12 on: July 07, 2022, 12:24:14 PM »

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



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« Reply #13 on: July 07, 2022, 12:52:13 PM »

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
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« Reply #14 on: July 07, 2022, 01:45:34 PM »

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
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« Reply #15 on: July 07, 2022, 06:36:06 PM »

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!
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« Reply #16 on: July 07, 2022, 07:13:19 PM »

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.  Grin

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".



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« Reply #17 on: July 07, 2022, 09:56:29 PM »

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…


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« Reply #18 on: July 08, 2022, 12:21:27 AM »

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
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« Reply #19 on: July 08, 2022, 06:12:34 AM »

cold shrink
https://www.powerandcables.com/product/cold-shrink/cold-shrink-tubes/
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« Reply #20 on: July 08, 2022, 11:30:33 AM »

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

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.


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« Reply #21 on: July 08, 2022, 12:44:06 PM »

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.  Grin

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
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« Reply #22 on: July 08, 2022, 02:17:05 PM »

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.  Grin

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 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.  More weight. I will tie the balun and feedline to the center insulator for support.  Keeping a sag in the dipoles will help 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!


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.😉



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« Reply #23 on: July 08, 2022, 06:58:04 PM »

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
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« Reply #24 on: July 09, 2022, 12:26:37 AM »

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


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