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HF J-Pole

from Mike Higgins, K6AER on July 24, 2017
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HF J-Pole
By Mike Higgins K6AER

I left my Colorado QTH and until I could erect a tower and beam at my new home, I decided to use the very tall trees at my new QTH. I placed a dipole up at 40 feet and it works well. I miss the DX that the beam would bring in and with the Sun Spot cycle heading to the bottom, 20 and 40 meters are the new, DX money bands. I decided to put up a wire J pole for twenty. I used one made from metal pipe back in 2001 and it worked very well.

There is nothing special about a J pole, it is an end fed wavelength vertical radiator that needs no radials. Just like its 2-meter brother but on 20 meters it is ten times larger. The bottom matching section is fed with 50-ohm coax. Bottom of the antenna is shorted and the coax attaches at the 50 ohm point in the matching transformer. The higher the attach point attachment, the higher the feed impedance. The antenna is shorted at DC and thus, P static is never an issue. I ran a nylon line over the top of the tree and the antenna is held vertically by the tree limbs. Leaves seem to have no effect on the radiation at HF. The long side is wavelength and the matching side is wavelengths

The 6 inch spreaders are made from inch PVC and spaced about every 2 feet for the parallel matching section. Drill the spreader and feed the wire through the holes on each end. Spreaders are held in place on the wire with good old vinyl electrical tape. The top of the matching section is tied to the radiator with parachute cord to hold up the matching section. Fifty-ohm coax is attached about 8 inches from the bottom with the center conductor connected to the long side and the shield attached to the short matching side. 2:1 VSWR is about 4 % of the Frequency. Also, the antenna can be grounded at the center of the shorting section for a lightning ground.

To tune the antenna just move the attach point up and down for lowest VSWR. Match should be 1.0:1 with ease. I used THHN 14 gage wire to build the antenna. I dont have $10 into the whole project. The antenna will handle 2KW easily. Mind you if you are running power the voltage at the top will be very high. Try to keep the last 10% in the clear and away from anything conductive.

In typical operation, I find the antenna to be 1-2 S units better on overseas DX. On stations, closer than 1500 miles the dipole generally works better. I was so impressed with the operation on 20 meters I built one for 40 meters. Now that antenna is almost 100 feet long and my tree is only 80 feet high. So, the last 20 feet bends over the tree top. No problem. The VSWR is flat and it too is terrific for DX.

Dimensions for the 20 and 40 meter antennas are shown below.

Member Comments:
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HF J-Pole Reply
by KA2UFP on July 24, 2017 Mail this to a friend!
material cost?
 
RE: HF J-Pole Reply
by NA4IT on July 24, 2017 Mail this to a friend!
In the article he says "less than $10"...
 
RE: HF J-Pole Reply
by N8EMR on July 24, 2017 Mail this to a friend!
Guess they assume you have a 98ft structure to hang the antenna from or have a lot of scrap metal to make one to keep it under $10...


 
HF J-Pole Reply
by KD4S on July 24, 2017 Mail this to a friend!
I interpret the article to describe a antenna made of wire, not metal tubing. That would keep the cost to a few dollars.
 
RE: HF J-Pole Reply
by SWMAN on July 24, 2017 Mail this to a friend!
Looks good but unfortunately I don't have room for it at my QTH. But thanks for sharing.
 
RE: HF J-Pole Reply
by K9MHZ on July 24, 2017 Mail this to a friend!
I hope you're using some kind of coax decoupling at the feed point.
 
HF J-Pole Reply
by KK5JY on July 24, 2017 Mail this to a friend!
Interesting approach to building a J-pole.

If I had 100'+ trees, I would have a vertical antenna for 160m, and another for 80m, and another for 40m. The problem with a J-pole is that it is 3x taller than a typical vertical antenna for the same band.

That said, if you have 100' non-conductive supports, why not?
 
RE: HF J-Pole Reply
by W3TTT on July 24, 2017 Mail this to a friend!
J-Pole - otherwise known as an End Fed Zepp. I built these for 20 and 40 using TV twin lead and doorbell wire for camping and backpacking. Thanks for the article.
 
RE: HF J-Pole Reply
by W3TTT on July 24, 2017 Mail this to a friend!
PS that waterview site looks ideal for radio - - - or just for relaxing!

Joe W3TTT
 
RE: HF J-Pole Reply
by AA4LR on July 24, 2017 Mail this to a friend!
Agreed that a 1/4 wave vertical would require less support height. The trade-off for the J-Pole is the lack of a counterpoise system (generally radials)

For that matter, one could just use a vertical dipole instead and save about 1/4 wave in height.
 
HF J-Pole Reply
by K6YE on July 24, 2017 Mail this to a friend!
Mike,

A very nice article on your part.

We moved again and waiting to put up the HDX-555 tower. Since I do not have any trees or other structures I am using the Tarheel on the back of my truck. I can hardly wait to get the radios, yagis, sloper, and amplifiers back in operation.

Keep up the good work.

Semper Fi,


TOMMY - K6YE

DX IS and CW RULES
 
RE: HF J-Pole Reply
by KE5PQR on July 24, 2017 Mail this to a friend!
AA4LR,
I'm thinking that if that's saltwater in the picture, he wouldn't need radials for a 1/4 wave vertical; he could throw a counterpoise wire in the water and be done with it. But I'd still choose the longer J-pole over a vertical dipole: it should save on coax feedline length and simplify the set-up.
 
HF J-Pole Reply
by KC3JV on July 24, 2017 Mail this to a friend!
For years I used and idea by Bob Dome (SK W2WAM)) that makes use of a top hat and transmission line to create a current node at the base (Effectively a half wave antenna). Although the impedance is not thousands of Ohms it is very high. You can use a 1/4 wave horizontal stub for matching or a 16:1 transformer and a chain link fence for a ground. That way you can use just about any height you have available.

Mark KC3JV
 
HF J-Pole Reply
by K0UA on July 24, 2017 Mail this to a friend!
Nice article Mike, I wish I had trees that tall. :( A good build and it sounds like you are getting some good results with DX contacts. Two thumbs up.

James
 
HF J-Pole Reply
by W4JLE on July 24, 2017 Mail this to a friend!
The quarter wave matching section can come off at 90 degrees reducing the height of the needed support.
 
HF J-Pole vs end fed Reply
by KA2UFP on July 25, 2017 Mail this to a friend!
end fed best wire antennas...less coax, cord, 40-20-15-10 63 ft...80-40-20-15-10 130 ft...inverted L, sloper,inverted V, inverted V with flat top, zigzag with 90* angles...1-1 swr
 
HF J-Pole Reply
by VE3KKQ on July 25, 2017 Mail this to a friend!
Nice simple to the point article.
You are fortunate indeed to have those handy trees.
Ham radio at its best, innovation with materials to hand, good job, OM.
 
HF J-Pole Reply
by W4AMP on July 25, 2017 Mail this to a friend!
Good article and looks like a nice new qth.
 
HF J-Pole Reply
by N7SWL on July 25, 2017 Mail this to a friend!
Great article! Nicely written and shows you have a solid understanding of your antenna theory. Looking forward to building one of these for my station. Looks like a great afternoon project.
 
HF J-Pole Reply
by ONAIR on July 26, 2017 Mail this to a friend!
How 'bout one for 80 meters? :)
 
RE: HF J-Pole Reply
by K6AER on July 26, 2017 Mail this to a friend!
Take the dementions for 40 meters and double it. Better off to use a standard vertical.
 
RE: HF J-Pole Reply
by AF6AU on July 26, 2017 Mail this to a friend!
With that lake right there, he probably could have just shoved a ground rod into the dirt a few feet, and went up 1/4 wave for any particular frequency. Or use a network and go up 5/8 wave. Lucky guy with such conductive ground.
 
HF J-Pole Reply
by NO6E on July 27, 2017 Mail this to a friend!
Thanks! I'll certainly try both the 20M and 40M versions. It looks inexpensive and easy to haul up into a tree.
 
HF J-Pole Reply
by NO6E on July 27, 2017 Mail this to a friend!
Thanks! I'll certainly try both the 20M and 40M versions. It looks inexpensive and easy to haul up into a tree.
 
RE: HF J-Pole Reply
by WA2ISE on August 1, 2017 Mail this to a friend!
You'd need a common mode choke to keep RF off the outside of the coax feedline. Like several turns of coax to make a coil.
 
HF J-Pole Reply
by HK1A on August 2, 2017 Mail this to a friend!
You don't need to put the whole thing vertical, the matching stub doesn't radiate, you can put it horizontal (1 - 3 or 4 feet above ground) or sloping up towards the base of the vertical section. That will allow you to use a hanging point a bit over half wavelength high instead of a bit over 3/4 Wavelengths.
 
RE: HF J-Pole Reply
by K9MHZ on August 3, 2017 Mail this to a friend!
ISE, I was wondering if the OP would mention that. Seems like a worthwhile project if someone has the vertical dimension to work with, so it would prevent some frustration for someone if that point was emphasized.
 
HF J-Pole Reply
by KA4DPO on August 16, 2017 Mail this to a friend!
Many years ago I built a Jpole antenna for 15 meters. From a mechanical perspective I would not try to go much lower in frequency because the length becomes difficult to manage. There are also some misconceptions surrounding these wonderful antennas. The idea that a Jpole does not need radials is true but it does need a very low impedance RF ground in order to preserve proper current distribution along the upper section of the antenna and the matching stub.
Jpoles are voltage fed (high impedance) antennas and are subject to detuning by almost anything near the 1/4 wave transformer section. That also means that there is very high RF voltage around the 1/4 wave transformer so don't let anyone touch it while transmitting.

Half wave antennas can be a potent DX getter but the Jpole can be cranky to tune.

I don't want to take anything away from K6AER, he wrote a very nice article on the subject but keep in mind a 100 foot vertical for 40 meters is a tall (pun intended) order.

My suggestion is that a Jpole would be a fun project for 17 meters and up where the lengths are manageable. Don't forget the RF ground.
 
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