The AM Forum

I've about decided that this inverted L is not living up to my expectations. Due to my situation, I really cannot install a decent enough ground radial system to do it justice. So, I'm thinking about going back to the classics (not Greco-Roman) and putting up a high dipole of sorts. If I build an OCFD, it will be easier to tune multi-band, but then I have a balun to worry about burning up, not to mention losses. OR, put up a standard all band 80-10 doublet fed with twin lead and use a link coupler. I really don't have room to install a 160m doublet unless I route the wire ends down the supports (in this case, trees).

Using high duty cycle modes @ 200W carrier makes we worry I'll burn up any balun I use, despite claimed power handling capabilities.

If this works, life will be better for everyone as folks won't have to strain to hear my PW signal.

Tnx!

Philip

Center fed doublet as long as you can fed with open wire line not crappy brown stuff.

Junkston Matchbox IS a balun. Some baluns don't burn up.

Phil,

You will be much happier replacing the L with a high, center-fed, flat dipole using a link coupled, balanced tuner. Forget the toroidal balun.

Twin lead is lossy for high swr, multiband use  - use homebrew openwire if you can.

If you really want 160M, consider a 180' long dipole with the ends sloped down. This will be a good compromise and let much of the current on 75M stay up in the air.  160M will work FB too.

T

180' indicates resonance at 2.6 MHz? Sloping the ends down adds top loading which makes it resonate lower???? Am I on the correct track here?

P

It doesn't have to be resonant to work.

The reason for the longer length (180' vs: 123') is to make the dipole more efficient on 160M.   Any time a dipole's size approaches 1/4 wavelength or less, (123' on 160M) its impedance drops so low that losses in the tuner and feedline can get significant.

The dipole as a 180' "skirted dipole" (flat with ends dropped down) will work well on 75M.    180' is about 3/8 wavelength on 160M and will work well there too, but as a slightly shortened dipole.  It's a small compromise given your space restrictions.  No ground radials are needed.

The higher bands on 40M and above will have cloverleaf and octopus radiation patterns, but will still be reasonably efficient.

T

T:

Roger on that. I think this is what I'm gonna go with. Now I just have to figure out the particulars of running balanced line to my shack. Having an upstairs shack will complicate my lightning reduction system (I never say "lightning protection system") grounding provisions. However, there is plenty of open attic space to run the twinlead.

tnx.

P

Sounds good, Phil..  You will be vely bery happy wid that antenna.   BTW, maybe you hear Bob / K1KBW on 75M down your way. He is running this same antenna, a skirted dipole.  He is very loud on 75M and also on 160M.

Maybe you already know this, but just to be sure, "twinlead" is that 300 ohm solid type brown feedline used with TV sets. There is also some for ham transmitting use. You do not want to use that.  Make your own 4" spaced openwire line with #10, #12 or #14 copper wire, that uses spacers every 2'-3' or so.. Plexi, Teflon and many other materials can be used for the spacers.  Also, stay away from the commercial brown plastic openwire that has the punched squares.  Making your own openwire with a good link coupled balanced tuner is what you need for an efficient multiband dipole antenna.

T

The antenna wire does not have to be of resonant length. But the system (antenna wire, feedline and tuner) does have to be resonant.

Open wire works well, but if you're lazy (like me), you could use coax.  I use coax fed dipoles everywhere; on Rattlesnake Island, and at home.  For multiband, I connect more than one dipole to the same feedline, and put the antennas as close to 90 degrees apart as possible.  This is very easy to do with 2 dipoles.  With 3 dipoles on the same feedline, you can't get all of the antennas 90 degrees from each other, but you can get to 60 degrees.

Or use a separate antenna for a band that isn't to big (wavelength wise).  I do that on 40 meters - use an individual antenna.

This is a personal preference as I've never had good luck getting the line to be balanced and getting a tuner that won't arc over.

If you're concerned about antenna currents on the coax shield, put a bunch of type 43 toroidal  doughnuts up at the center of the antenna and run the coax up through the middle.  The inductance created by all of those cores will break up the antenna currents and eliminate coaxial radiation.

Dirt simple and practical.  That's why I use it!

Found this after looking around...

http://www.73cnc.com/category_s/42.htm

Sure, those will work FB for making openwire.   You can get the 500' spools of #14 THHN stranded wire at Home Depot, as they said.

As Steve said, coax feedline is a great solution too using separate dipoles or multiband fan dipoles.

 For years I ran five separate ant tuners with #10 open wire for quick band switching. But for the last 20 years I have run 75 ohm hardline coax for all antennas. It is buried underground in 4" PVC piping.   Flexible coax wound on a 4" to 6" pvc pipe can be used as a choke at the dipole feedpoint to supress shield currents.   (As well as using ferrite cores)

The advantage of using separate coax-fed dipoles is that you get control of your radiation pattern. It will always be a predictable broadside figure 8.  With a multiband single legged dipole with ant tuner, the number of pattern lobes increases with frequency.  So a 160M dipole used on 40M will have four lobes...  a 160M dipole used on 10M has sixteen lobes - and as many sharp nulls. Pot luck.

Good luck with the project.

T

This thread has caused me to think about my situation

I have about 200' of space between two 60' trees and I want to work 160 - 10. Currently I have a 140'+ doublet fed with open wire & a link coupled tuner.

Results on 75 are OK, 40 so-so & the higher bands iffy based on lobe direction.

Would there be any theoretical (and hopefully practical) advantage to lengthening the wire to say 190'-200', and also adding additional (fan) dipole wires for higher bands of interest while keeping the balanced feed.

I would think that this would give me the desired addition of 160 but would the addition of fan dipoles for the higher bands help, hurt or have no effect?

Has anyone used and or modeled a fan diople fed with open wire?

Hi Terry,


As you thought, adding length to the 140' dipole will increase its impedance up to 40 ohms or so and make it more efficient on 160M - as a figure eight pattern.

Now as for adding the extra dipole legs for the higher bands using coax....    A set of dipoles on the same feedpoint will approximate separate dipole radiation patterns, but not exactly.  On some frequencies certain legs may hog more power than others and distort the pattern from a perfect figure 8.   But in general, multiple legs is a way to control the pattern into a figure 8.   You would need to model it to see the variations on various freqs.   For example, you may find that the lower band dipoles hog a lot of power on 15 meters and start to produce  multiple lobes. The "even" bands should fare much better.  

For an open wire fed fan antenna,  let's say we have 450 ohm line and multiple fanned dipoles...  The normally 70 ohm dipole legs will not be a match for the 450 ohm line at the desired freq.  How will that affect the radiation pattern if at all? Will the proper leg still take power at the desired frequency compared to the other legs which may be a better match for 450 ohms?  I'd have to model that to see or maybe someone else knows the answer.

The bottom line is that we want the proper 1/2 wave dipole leg to take most of the power at the desired frequency to produce a nice figure eight pattern.  A similar problem occurs when we use 450 ohm open wire rather than low impedance 50 ohm aluminum angle or a double boom  to feed a log periodic.

T

On 160 meters, with a height of 60 feet, the azimuth pattern will be omnidirectional. The antenna is too low to yield a figure-8.

Yep, true.  160M pattern optimization is almost a mote point. (And 80M too)   160M  efficiency increase would be the reason for lengthening it.  Though, at 60' high the ground losses are beginning to increase to significance, like using an 80M dipole at 30' high.  Good reason to get it up to 90' or more if possible.

T

The configuration you mentioned "skirt dipole" is also termed an "inverted U". The rational for its operation was that the highest current region (and radiation) is near the center. Operational characteristics by folding down 33-50% of the ends doesn't affect things all that much.

so
Well 60' is my max height so I guess I'll forget 160.

Maybe a loaded verticle this fall, but I hate radials.

Possible drawback at my qth is only 60' height available and it will be impossible to run the stuff from the feed point entirely clear of foliage. Lots of trees on my property.

Terry,

Don't sweat it - I know of guys running 160M dipoles at 30' who do very well.  For local work, most of us will have omni-directional patterns, which is probably a good thang.   To get a good >600 mile DX signal on 160M under average conditions, we need either a well radialed vertical in the clear or a very high dipole.

So you will be fine on 160M at 60' using a skirted or inverted U dipole out to 300-500 miles or so.
The regular AM group here on 1885 Thursday nights are all within 300 miles, so low dipoles do FB here.


K1KBW runs a skirted dipole at ~ 70' fed with openwire.  Two weeks ago he was loud on 1885 - at times within 5 dB of Chuck / K1KW who runs a dipole at 140' at the apex.  Running similar power that night.  Bob is closer to me, but still, it's a tremendous antenna system for local 160M work.

T

Wow, just read this analysis using windowed polyethylene dielectric twinlead.....

http://users.triconet.org/wesandlinda/ladder_line.pdf

Not intended as a hijack, but a shot for opinions: ???

About 400' length dipole @ 60' AGL. 

Made up from #6 hard drawn copper, center fed with same on 6" porcelain insulators to husky HB balanced matching unit.

??

73DG

Thanks Tom.

By a "skirted dipole" I assume you mean i should let the ends drop down vertically to make up the additional length necessary to get to full size 1/2 wave?

In my case that would be about 25' of vertical on each end. The bottom of the vertical wires would be about 35' off the ground.

Or should I just leave the wire at 200' in length and keep the ends 60' high - as far from the ground as possible?

Here are some MMANA GAL test runs. 60 foot horizontal, 30 foot vertical each leg, 60 foot height horizontal section.

Continued...

Last batch

Hi Terry,

On 160M, the difference between 200' at the same height and hanging the ends down will not affect the pattern much.  But it will have an effect on the higher bands.    If you use the antenna for 40-10M a lot, then I would keep the whole thing at 60', 200' long.  If it is just a 160-80M antenna, then drop the ends so that 160M is most efficient.  The 80M band will have some slight bi-directional gain.


Dennis, that sounds like a vely efficient antenna, being made entirely of #6 wire.  I once had a 123' dipole fed with open wire just like that. My friend calculated the loss difference to be insignificant compared to using #12 wire.  But if the antenna were a shortened dipole, like 60' long used on 80M, it would make a big difference.  The higher bands will have many high current spots, so it will help there.

Anyway, 400' is quite big.  On 80M, 310' long is about the longest we can go before the bi-directional figure 8 starts to get significant side lobes. So on 80M, you probably have four lobes.  (two main and two smaller) On 160M, you would see a dB or so of bi-directional gain, IF the antenna was high enough.  On the bands 40M - 10M it would break into more lobes and nulls... and have more directivity off the ends.

T

Thanks, Tom.

I am planning now, and have a lot of room for this.  I'll take your advice and shorten up the plan a bit.

I was going to put up just one antenna at present, and wanted it to be the best I could get with simplicity of construction.

73DG

Dennis,

Yep, it's not how much wire is in the air, but how it is phased.  We can have a 5000' long dipole, but if the lobes are many and facing in the wrong directions, it will have negative gain compared to a simple 1/2 wave dipole in the right direction.   The idea of lots of wire in the air applies to getting needed efficiency on the LW frequencies, etc.   Once we have 1/2 wavelength of wire, on the higher ham bands, it's all about phasing.

If one had the room, I still think a pair of phased, coaxially fed dipoles at 50'- 90' high is the best antenna for the bux on 80 and 40M.   Switch it NE, SW or cloud-burner modes.


Phil's 180' antenna plots above are revealing. It looks good on 160, 80M and 40M.    180', no longer,  JUST works for 40M.   But on 20M - 10M  there's more radiation off the ends of the dipole. That is OK if that's what we want, but remember that on 80M we are radiating broadside.  We will be loud in Calif on 80M and 40M -  and loud in Florida on 20M - 10M.... :-)     That's the advantage of separate dipoles that can be faced figure-8 broadside in the desired direction.  

Actually that skirted dipole is not as lumpy on the higher bands as I  thought. Maybe the skirted ends help. It's a fine multiband antenna, really, compared to the commercial gimmick antennas out there.. We just need a good, heavy duty link coupled balanced tuner to finish the job.

T

Coax is for sissies.

Dennis,

Another thing, since you haven't put up your antenna yet....

The longer the antenna, the higher above ground it needs to be to achieve the same vertical take-off angle.    For example, a center-fed 240' dipole on 80M may have to be at 80' to show the same vertical takeoff as a 123' dipole at 60'.  Probably has to do with higher ground losses due to higher coupling of a longer antenna to Earth ground.

So, it might even be better if you make your dipole 240' at 60' high to cover 160M and call it done.  A reasonable vertical take off angle is very hard to get on 160M, so we need all the help we can get.

T 

BTW, those plots are combined H+V.

P

I'd opt for the flat-top as high as possible for best 160 meter performance, unless you want to use coax. The ends hanging down may help avoid some pattern break up on the higher bands, but there's no guarantee. I guess it depends on how much you plan to operate on the higher frequency bands, and/or if you can/will put up a separate system for 20-10 meters.

My 160 meter horizontal antenns over the yeas have never been more than 70 feet high (some in the 50 foot range). I have still been able to make 100s of AM contacts (5-10 contacts nearly daily back in the 90s), never running more than 300 watts. On slop bucket I have something like 40 countries worked with a 70 foot high dipole.

Get on 160 and see what happens. If you want to try a vertical or Inverted-L later, you can.

My situation is we have two granite hills on the acreage, and I was going to suspend it between them. 

Can't do to much to work a different alignment, so a pretty much N-S stretch is it.

No matter how it will play is better than not being on at all. ;)

Besides, there are a lot of Watts waiting in the wings for their time in the limelight.  Now if I just had something important to say then....

73DG

By a bizarre alignment of the planets or other mechanism, I already possess most of the parts to make a balanced tuna; HV 500 PF bread slicer and an EF Johnson 28 uH roller inductor. All I need to do is find another EF Johnson #229-203 roller inductor and we're cooking with gas.

Philip

Fleep,

    It isn't necessary to use expensive ganged roller inductors. That's nice to have but a pair of identical coils works also. I've wound my own in pairs several times.

The balanced design can be a a lot of work to find settings the first time but well worth the effort.

Better than link tuners for band cruising because they are not bandpass filters.

Can be configured to keep all wire in the air at D.C. ground. Some people like this for static dissipation. Yeah that can be done with a pair of resistors on a linky setup.

Not likely to wind up with a power robbing awful Q situation as you can with high pass T networks along with some poorly thought out link setups.

Can be built with extreme impedance matching range and work well. 

With my history with Thor, I'm already performing some thought experiments on how to ground this antenna prior to entry into the house. Reference paragraph 1:

http://www.iceradioproducts.com/30.htm

So I will need to bring the ladder line close to ground, anchor near a ground rod, install lightning arresting/ground means, then route back up to eave, through attic, and terminate at my second floor shack. I also do NOT intend to install the vertical run up to eave directly adjacent to the downward lead to avoid flashovers.

The final version will enable me to completely disconnect/isolate the portion of the feedline that enters the house while shorting/grounding the lead from the antenna.

The center will be supported by a tree at about 60'. The ladder line will drape away from the tree at about a 15 degree angle to the vertical.

Any pitfalls to my approach??

Matching rollers aren't always expensive:


http://www.ebay.com/itm/E-F-JOHNSON-229-203-ROTARY-INDUCTOR-/251582035396?pt=US_Ham_Radio_Transmitters&hash=item3a937535c4

Got it. Thanks for the link.
 ;D

That's a good deal and a lot less than they were Jeff. A couple more deals like that and you and I can afford a classic Mercedes.

Best price I've found on a 500' roll of #14 AWG THHN/THWN is 40 bux @ Lowes/Home Despot. A local electrical supply house had it for almost exactly the same price.

Only problem I've noted in the past is the outer coating flakes off quickly due to UV and uglifies the whole shebang.

I've used Home Depot wire for antennas, and after roughly 15 years, it still looks fine.

But, if UV is your pressing issue, go here:
http://www.dxengineering.com/parts/dxe-antw-500

Must have been the brand I was using. Anyway, found a copy of Ed Bigbie's article (I knew Ed personally and he lived not that far from me) quoted from friend Mark's blog:

http://ka4cid.blogspot.com/2008/12/w4mmq-legacy-balanced-antenna-tuner.html

What happened to the pair you had?

THHN can get ugly. Lighter colors seem to take longer shedding the clear coating.


I've had 3 sets in use over the years. One was sold on epay to a ham in Studio City Ca. Sold the second set to members here.

The pair on the K3L 2005 / W2A coupler is not really a pair. The pitch and turns count are different. No effort was made to gang any.

Still using the different ones as a band cruiser. Find the necessary values and build a permanent setup after.

 

Nah, I was refering to the "classic Mercedes" part of the post, Dave...

Thread needs an NPO. I still have both W-140s.

Somewheres out on the land is our '59 219 ???.

Gotta go look for it.

73DG

Regarding THHN Building Wire for antennas;

Black insulation holds up quite well.  In a year or three,  the clear Mylar(tm)/polyester coating on the wire delaminates,  and falls off,  but the black PVC insulation seems to hold up.   Some of the black insulated THHN antennas,  here,   have been up for a couple of decades,  and seem to be going strong.

Had tried lighter colors,  and green insulation.  On these antennas,  the PVC  started rotting in a few years.

YMMV.     Have Fun,     Vic

May wait to the fall to do all this work. Frankly, this bod doesn't do well in high heat/humidity anymore. One has to do lawn work by getting up prior to the crack o' dawn.

I visited Home Despot this past weekend to acquire some wire (pronounced "war", rhymes with "tar"). The wire was advertised on the internet at around $40 for a spool of No. 14 AWG THHN stranded, 500'. Upon entry, I noted that nary a spool was anywhere....however, loose wire was for sale by the foot on their vertical lazy susan at 0.25/foot. This works out to more than 3x the price per foot for a prepackaged spool. I left the store and made a note that Home Despot will be the last on my list for various and sundry electrical supplies.

In any event, frequent spectacular storms this weekend precluded any antenna work. The ladder snap kit arrived on Friday.

PAN

Home Depot is last on my list of the big box stores.  In this area Menards has excellent pricing and stock levels and Farm and Fleet often has good prices on electrical stuff.  After that I hit Lowes and to me Home Depot is a great place for soccer moms to shop for generic decorating crap. :)

Just put on your scruffy clothes and go steal some copper wire out of an under construction home like the meth heads :(  Two years ago one or more of them stole about $5,000 worth of copper and did over $100,000 in damage to a gravel quarry operation in the area.  Unfortunately not enough of them try to steal live wire and fry themselves in the process.

I designed a project about 10 years ago that consisted of converting a Publix into a shopping mall. Complete gut and redesign. Ton of electrical, 277/480 and 120/208, lighting, power, data, fire alarm, mucho blinkies and flashies, and worth lots of grey hair. One morning the foreman came on site and noted that all of the already pulled copper wire (about 50K worth) was missing. It was an inside job.

Subs these days typically install covert CCTV cameras and alarm systems. Copper prices have gone thru the roof due to Chinese demand and other factors. Today the price is $3.27/pound.

Lowe's pretty much carries the same stuff in a variety of colors for around $38:
http://www.lowes.com/pd_293645-295-11579058_0__?productId=50149804&Ntt=wire+14&pl=1&currentURL=%3FNtt%3Dwire%2B14&facetInfo=

(http://images.lowes.com/product/converted/032886/032886892653lg.jpg)

Yep.....they were out too. The local electrical supplier near Ft. Stewart had what I needed in stock at competitive pricing. Big plus: small stores are not crowded.

A soldier stole some wire on-base here. I was asked to testify (as an electrical engineering expert) but never called. I think the guy is in Leavenworth now. I don't want to spend the remainder of my adult life making high quality furniture at that place as well as forced participation in activities I'd rather not discuss in a "G" rated forum.

Construction underway using Ladder Snap...finished up 100 feet of ladder line in about 3 hours.

Where's the LIKE button?

 Looks Good! I'm thinking of something along these lines myself, Looks like you have a lot more space than I do with my 100' X 50' typical Bay Area lot.

 Right now I have a fan dipole, section for 80 and 40, I'm using a tree on the far corner of my property line that is 10 feet in from the corner on the property line. The dipole is in a very tight V, you gotta fit it where it will fit!

 The plan is the have a local tree guy put a redwood 2X4 up at the top of tree, it's a Redwood too, so I can gain another 15 or 20 feet in height. Once that is done then it's time to rethink the antenna, 600 ohm ladder line using the spreaders you have and a 130 foot dipole and my Johnson Match Box.

 When I get closer to doing the antenna I'll probably post here for some advice.

Finished up today prior to temps getting into the 90s. Its been pow'ful warm here.

Used a dog leash anchor as well!

Notice that the slits in the lawn chairs were almost exactly the width needed! Really helped in getting the spacers at waist height for assembly.

Very nice.
"Stairway to Heaven"

The die has been cast and we've crossed the Rubicon....I took down the venerable inverted L and will erect my open wire feedline doublet soon.

Other than on 160 meters, you'll likely have a far better signal. Enjoy!

160 radiation model plots

Got the 180' doublet about 50% installed this past weekend at which point my friend's "Big Shot" malfunctioned and we adjourned due to the heat.

Here is a Big Shot

https://www.youtube.com/watch?v=OIitgJ0M5dk

The apex is going to be at least 60' up and the two outlying trees are far enough apart that we will not need to droop the ends. The final configuration will be an inverted vee with about a 150 central angle.

Woke up Monday morning with a whole bunch of itchy red bug bites....they must be impervious to DEET.

I figure this will be a 3 weekend project. Next weekend, finish erection. The following weekend, run balanced line into the attic and to my Mad Scientist Shack of Doom. I think I may have a proper Frankenstein Switch lined up as well.

Chiggers are fun, are they not?   ;D

Clear nail polish over every chigger hole. Asphyxiate the lil' buggers.
Red nail polish if you want to clear the room.

Oh, yes they are! Still need to chop up a felled tree into little pieces with a chainsaw. I am putting a lot of effort into this so it ups the likelihood it won't function well at all.

A friend and I finished up the antenna erection. The apex is at 60'. We'll work on the feedline routing next weekend. Looking good!

FINISHED!!!

Completed routing of open wire line through the attic to my shack. Seems to load up fine using the Heathkit SA2060. No arcing or sparking at 1200W. My only complaints.....

1. Insulation sure makes you itch BAD.
2. Roofing nails don't feel good at all on the bottom side when they scrape over the top of one's skull.

We'll do some "smoke tests" tonight and see how it plays.

...addendum

Contacts on 40m...statements such as "hearing you 10x better than I ever have".

So preliminary results suggest the doublet is cooking with gas.

Philip

hi Feeleap ....heard you last night on 75 mgr SAMRC net on 3885 .... at least an s unit stronger here than befo' ... one thing, do you have some sort of lightning arrestor on that open wire befo it comes in the attic .... I used a small piece of aluminum angle bracket with 2 tractor spark plugs (no resistor element, please) to ground ....has taken 2 hits to the tower so far with no ill effects ...recommended

My solution is simple. I have a quick disconnect for the aerial run to the house in the middle of it. It's low enough to reach. So, when not in use, I disconnect the antenna side of the feedline and move the ends to a very large ground rod directly below the suspension point. I don't plan on leaving this behemoth connected while away from home during prime lightning season.

I also got a tetanus booster yesterday as I was a year overdue: didn't want to take any chances on that nail-head injury.

Rats. Roller inductor No. 2 has a bent shaft end. Gotta try to straighten it for the balanced tuna.