Looking for Old J-Pole Design - Elmers Forum at eHam.net

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eHam.net Forum : Elmers : Looking for Old J-Pole Design

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Looking for Old J-Pole Design	Reply
by K1YU on July 22, 2004	Mail this to a friend!
About 30 years ago I built a J-Pole "like" antenna for 2m use. I have since lost the antenna and the plan. But, the performance was very good, and I'd like to build another one - but have not been able to track down the original design article. I suspect it was from QST or 73 mag, but really don't remember. I built it for 2m and I don't recall if it actually worked on other bands. As I recall the design, there were 2 vertical elements (one short, one long) attached to a conductive base - very much like a typical J-Pole. The unique feature however was the feed mechanism. The SO-239 was mounted to the antenna base. The center conductor was attached to a length of 12ga, insulated solid copper wire. The length of wire was then coiled around one of the antenna elements. Ringing any bells?

RE: Looking for Old J-Pole Design	Reply
by WD5G on July 22, 2004	Mail this to a friend!
I remember seeing that in one of the ARRL's Hints&Kinks books. In fact, I've been using that same coupling method on my J-pole for 10 years, or so. When I get home this evening, I'll find the dimensions for you. 73 de Dave

RE: Looking for Old J-Pole Design	Reply
by WD5G on July 22, 2004	Mail this to a friend!
The information you are looking for is in the 13th edition of the ARRL Hints&Kinks book on page 7-31. It describes using loop coupling on J-pole antennas. There's no magic on the J-pole dimensions, just use the standard dimensions. I used 5/8" copper pipe to withstand the Oklahoma winds. The magic is in the coupling. The article indicates a loop that is 1 3/4" between the vertical sides, and 5 1/2" between the horizontal sides. They suggest putting the bottom side about 3/8" above the bottom part of the J. The article suggests using insulated #14 wire. It's interesting that there is no electrical contact between the J-pole and the loop. This is the best way I've found to match J-poles. 73 de Dave

RE: Looking for Old J-Pole Design	Reply
by K1YU on July 23, 2004	Mail this to a friend!
Dave, thanks for tracking this one down. Sorry, but I am having trouble seeing the coupling network. Any chance you could try describing it a bit more, or emailing a drawing? 73, John

RE: Looking for Old J-Pole Design	Reply
by WD5G on July 23, 2004	Mail this to a friend!
John, Just imagine a rectangle that is 1 3/4" wide and 5 1/2" that is laid over the bottom of the J so that the bottom edge of the rectangle is 3/8 " above the horizontal part of the J. Feed it with 50 ohm coax at point where the horizontal part of the J and the long part of the J intersect. Seal the solder connection where the coax and the loop intersect with RTV, etc. If you'll send my your email address, I can probably scan the picture for you. 73 de Dave

RE: Looking for Old J-Pole Design	Reply
by WB6BYU on July 23, 2004	Mail this to a friend!
John - I know what you mean - the feedline is actually capacitive coupled to one of the elements (it doesn't really matter which one) by wrapping a length of insulated wire around it. This is a form of gamma match and I have used it on quads and yagis over the years with good results. I know I have a drawing of it at home, and I'm sure I've seen them on the web somewhere. I saw a number of them in the Santa Barbara/southern California area. And I think I still have one of the machined aluminum brackets out in the junkbox with holes for the mounting mast, the two vertical elements, and the SO-238 connector. - Dale WB6BYU

RE: Looking for Old J-Pole Design	Reply
by KB1LKR on July 23, 2004	Mail this to a friend!
What is the advantage of the gamma match vs. direct connection w/ a J-Pole?

RE: Looking for Old J-Pole Design	Reply
by K1YU on July 23, 2004	Mail this to a friend!
Hi Dave - guess I am a bit "thick" today - still cannot visualize it. My email is goutboy#comcast.net - just replace the # with a @ - thanks!

RE: Looking for Old J-Pole Design	Reply
by W8GAS on July 25, 2004	Mail this to a friend!
http://www.hamuniverse.com/jpole.html

RE: Looking for Old J-Pole Design	Reply
by WB6BYU on July 26, 2004	Mail this to a friend!
I like the "twisted wire gamma match" because it is easy to adjust: slide the wrap up and down the element to adjust the resistance, and unwind turns to reduce the capacitance. And it avoids having to make a direct connection to the element, which can be an advantage when they are of different metal types (ie. copper and aluminum), or are hard to solder. Also, the mobile J-poles that were using this were usually made from stainless steel CB whips. Both whips were terminated in a machined aluminum block with set screws which made it easy to adjust the length of each whip individually. The block was then attached to a mast of some sort: I think the lower mast sections for a Hustler mobile HF whip were often used. Again, the twisted wire eliminated the need for an additional clamp to connect the feedline to the stainless whips. The flexible whips are more appropriate for mobile use than the standard copper pipe version. There are many different ways to build the J-pole, and the differences among them often are more due to the materials, skills, and equipment available to the builder than performance factors.

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