*Compact Full Sized J-Pole*
I have no idea why this popped in my head. I was in the bathroom (you fill in the blanks) and just happened to look at the shelf and saw a ½" male coupling for ½" copper pipe. "Screw together J-pole" entered my gray matter. DUH, YES!!! So simple!
Some hams such as myself like to have field expedient antennas for ease of portable use or emergency communications. There are roll up J-Poles made of RG-58 coax and 300ohm twin lead (I’ve never had any luck with them) and tons of other field antennas. I’ve been licensed since 1997 and visited hamfests and many ham websites and I’ve never seen a compact "REAL" J-pole. This "could" be a whole new idea, but I doubt it. If it is, you saw it FIRST at the AlphaRubicon. So here we go.
First of all, build a regular J-Pole. (I don’t see why this wouldn’t work for a J-pole on 6 meters, 70cm or whatever.) You can get those instructions right HERE. After you’ve built the thing then it’s time for modifications. No reason this can’t be done on an existing one.
You’ll need to get two ½" male couplings and two ½" female couplings (they screw together). Oh, that didn’t sound good did it….well, you get the point :o).
Fittings.
I cut the driven element at the end of the ground element and soldered on a MALE fitting. This way when it rains, it can’t enter the coupling. I soldered on a female fitting to the piece I cut off.
Then I used the top piece of the driven element to measure from the fitting toward the bottom of the J-pole. I then cut the bottom at that mark and soldered on another set of couplings. Again…make sure the female is on top so water runs off. If you do this part right, there’s NO WAY you can screw the wrong element to the wrong place.
From top to bottom we have- top of driven element/ center piece/ bottom element. This baby screws together in seconds and is just as rigid as a regular J-pole.
Convenient huh….breaks down in to 3 small sections. Easy to throw in a trunk or back of a car. (watch the male threads not to ding them). You can always buy 2 more female fittings to screw on just for protective covers when it’s taken apart.
You’re not done yet. It’s time to compensate for the extra length added by the coupling. Screw the thing together hand tight (think field use…you might not have tools…no need to crank it tight with a wrench anyway). Then re-measure the driven element and cut whatever’s required from the top. The bottom section shouldn’t matter. I took it completely off and it didn’t affect the SWR.
It’s on the air and working!!
I propped it up in the living room and put it on the air with 45 watts. My worst SWR is 1.6 and that’s in the very top of 2 meters….which I seldom use. I figure once the antenna’s outside and in the clear the SWR should drop a little anyway. I had a couple of contacts and it was doing just about as well as the ¼ wave in the attic.
So I guess it’s official, tried and tested that this works.
FACTA NON VERBA
73’s
Jaden
www.alpharubicon.com
All materials at this site not otherwise credited are Copyright © 1996 - 2005 Trip Williams. All rights reserved. May be reproduced for personal use only. Use of any material contained herein is subject to stated terms or written permission.