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Bringing the K6AER HF J-Pole to Life

from Andrew Ellis, NO6E on November 16, 2017
Website: http://www.no6e.org
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Bringing the K6AER HF J-Pole to Life
By Andrew Ellis, NO6E

Intrigued by Mike (K6AER) Higgins' eHam article on HF J-Poles, I decided to bring his design to fruition. Not everyone has trees or support structure to hang a 50-foot vertical wire antenna – but some of us do! It's not the equivalent of a beam and tower, but one does what one can.

Many, if not most, hams have built J-Pole antennas for VHF or UHF. They have a lot to offer – no ground is plane required, there's DC ground is through the antenna and good bandwidth. Still, like many others, I had never considered building one for HF.

Mike's article has all the info one needs to build one. I felt that the most structurally-sound realization would be to use a single piece of wire for both the antenna and the matching stub. The 20M version of Mike's J-pole, then, needed wire amounting to:

48' 9” for the main element
16' 5” for the stub.
6” for the space across the base between the two
3” or so to allow for connecting loops at the ends of the element and stub.

That all adds up to about 65' 11.5”. In the interest of getting it up quickly and cheaply, I used green-jacketed THHN #14 solid copper wire. It's $0.29/foot at my home center, but less than $0.13/foot if you buy a roll of 500'. That's what I did. You can probably do better on the price.

The spacing between element and stub is 6”. Being a natural cheapskate, I realized that a $.99 wooden yardstick could yield five 7” spreaders, with 1” left over. My materials were chosen!

The first step was to cut the three yardsticks into fifteen spreaders. I used an inexpensive plastic miter box and back-saw, but any kind of saw would work. Neatness counts, but not for very much!

Stacking five or so spreaders together to save time, I drilled 7/32” holes about 1/2” from each end, yielding the 6” spacing I wanted.

Pausing only to admire my hairy legs, I measured to see where the bottom spreader (with wire connecting element and stub) went along the wire, then threaded the newly-drilled spreaders over both wires.

The bottom spreader is made up of two pieces of wood, the others from one each. Making a virtue of sloppiness again, I spaced the spreaders about 16” apart, though this is far from critical.

This photo shows that the 20M J-pole is, well, pretty tall! The bottom spreader (at the bottom of the photo) is 49' from the top of the main element, marked by the distant yellow tape measure.

This photo shows the top of the matching stub and the top spreader, 16' 5” from the bottom spreader. The main element (on left) continues.

To fasten the spreaders to the wire, I first used small (red) nylon cable ties. Once everything was placed, and after receiving assurances from the manufacturer that it was not actually made from gorillas I added a blob of “Gorilla Glue” to each spreader penetration.

The only tricky part of the 20M J-Pole assembly is making the feedline connections. K6AER's article suggests they be 8” above the bottom of J. I decided to strip enough wire to let me connect the feed over a 4” range, from 6” to 10” above the bottom. Stripping the middle of a wire is tricky. It's easy to nick the conductor, which would weaken it a lot. Using a felt-tip marker, find where the beginning and end of the strip should be. With a sharp hobby knife, cut through the insulation around both ends of the area to be stripped. Cut a couple of lengthwise slits between the marks, and then carefully remove the jacket between them. Take your time!

I used the feed from an old doublet. It's made of RG-58 coaxial cable with a few ferrite beads for isolation. (The J-pole is a balanced antenna, so some kind of common-mode choke should be used.) As Mike's article notes, the feedline can also connect electrically to the middle of the base, but I didn't do that.

The last photo shows the J, very much not vertical, hanging from my 135' 80M doublet for SWR testing. It looked fine near the bottom of the 20M band, though it was best with the feed about 10” above the base instead of 8”. That's within tolerance, and one reason for allowing a range of tap points.

The final steps are mechanical: Form a small loop (say, 1” in diameter) at the ends of the stub and element. Tie a support line (I use “Paracord,” a strong nylon line with dacron braid over it) to the main element, and then extend it to the end of the stub and to the top spreader. This helps when hoisting the antenna by keeping the spreaders close to horizontal.

I soldered the connections from feedline to antenna and ends of the main element and stub. They were covered with “Brush-On” liquid electrical tape, which is available a most hardware stores.

Finally, I sprayed the sides and, especially, the end-grains of the wood spreaders with primer paint to keep them from absorbing water. That's a big issue here on the Oregon coast, where we receive almost 60” of rain each year.

Over many years, I've learned that getting an antenna up in the air to try is more important than making sure it will last for decades. There's plenty of time to beef up the structure later if it proves to be the greatest gift to HF since sliced bread.

For a “quickie” project, I'm very pleased. Early tests on-air suggest it may be better on distant stations than my 20m reference antenna, an 88'-long Extended Double-Zepp (EDZ) at about 40'. We shall see! It seems unlikely that the 100'-tall 40M version would work here. Still...

Many thanks to K6AER for suggesting this unusual (if large!) HF antenna. I'll report on results once I have more experience with it.





Andrew Ellis, NO6E
Rogue River / Bandon Oregon
no6e@no6e.org
my blog: www.no6e.org

Member Comments:
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Bringing the K6AER HF J-Pole to Life Reply
by KJ4DGE on November 16, 2017 Mail this to a friend!
Thanks Andrew, very good article and pictures are always a good way to share the experience. I too am considering a J-pole for 20 as a vertical since I moved to a much smaller lot to hang wire in. Good step by step instructions, keep writing you have a knack for it!

73

Greg
 
Bringing the K6AER HF J-Pole to Life Reply
by W5DXP on November 16, 2017 Mail this to a friend!
This antenna is very similar to the Zepps of old. The only apparent differences is that this antenna is matched to 50 ohms and goes up instead of down. The 1/4WL matching section has some common mode current and does radiate.
--
73, Cecil, W5DXP.com
 
Bringing the K6AER HF J-Pole to Life Reply
by N0XAX on November 16, 2017 Mail this to a friend!
Nice article Andrew! Building wire antennas is fun! And you learn as you go about building the antenna. I have constructed many wire antennas through the years. And the best of all they are cheap!! Nice presentation too!
 
Bringing the K6AER HF J-Pole to Life Reply
by K8ALM on November 18, 2017 Mail this to a friend!
Very nice article. Thank you. Looks like you had fun with this one.
-K8ALM
 
Bringing the K6AER HF J-Pole to Life Reply
by W4WDM on November 18, 2017 Mail this to a friend!
I’ve often thought about building this antenna. It looks like you did a good job with yours, thanks for sharing it...
 
Bringing the K6AER HF J-Pole to Life Reply
by ONAIR on November 19, 2017 Mail this to a friend!
Nice article! Always fun to homebrew antennas. Reminds me of the time when I built a 40 Meter ground plane! ;)
 
Bringing the K6AER HF J-Pole to Life Reply
by NO6E on November 20, 2017 Mail this to a friend!
Hmm. 40M ground plane, eh?
 
Bringing the K6AER HF J-Pole to Life Reply
by KA4NMA on November 28, 2017 Mail this to a friend!
Can. J-pole be mounted horizontal? Any 6m and 10m plans using window line? Can it be multiband and is so length for 16-6m mounted horizontal?

Great article

Randy ka4nma
 
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