2 Meter J-pole tunning

[KD2GOE]

I made a J-Pole antenna but I am having a hell of a time getting the match down on 145mhz right now my swr is 1.2:1 is at the top of the band 148mhz.. the tuning stubs seem to do nothing and I adjusted the feed point all over the place, this is the best I can get right now.
here is a video if me sweeping through 2 meters and some pics of my J-pole any tips would help...

https://www.youtube.com/watch?v=btRJ03Z3GOg

 

[vo1ks]

I've had better success with the shield on the long section and the center conductor going to the short stub. It may also work better if you minimize the horizontal part at bottom of the J, keeping the two vertical elements much closer together. Keep the shield length very short, to the point of just barely hanging out of the jacket. Install a multi turn choke balun beneath the bottom of the J section.

Never been a fan of the antenna, but keep messing with it and it should work.

 

[Captain Kilowatt]

Looks like the antenna is a little short. You may need to add a half an inch to an inch to it and retune from there.

 

[vkrules]

Swap the connections over ( I know some say it doesn't matter but I found it does)fit a choke and try again. If it still doesn't work lengthen the 1/4 section a little.

 

[KD2GOE]

Ok ill try fliping the wires see what that will do. if that dont work ill shorten the center section... the shore and long pipes have 4" tuning stubs that are not all the way out.
i have had the long one out all the way it did not help. The short tube will change the SWR.

 

[KD2GOE]

the coax I'm running is Dave's bery flex

 

[Beetle]

the coax I'm running is Dave's bery flex

Doesn't matter. 50 ohm coax is 50 ohm coax.

 

[KD2GOE]

Doesn't matter. 50 ohm coax is 50 ohm coax.

yeah I know but it may be info that matters

 

[KD2GOE]

ok I flipped the feed point and I got it down to 1.3:1 at 144.95 so that is good but when I compare it to the 1/4 ground plan I have I am giving my friend 2 more s units with the 1/4 wave

 

[KD2GOE]

I am going to play with it some more... some thing is not right the 1/4 wave should I be doing way better than the j pole....

 

[Robb]

My experience with j-poles taught me they can be fussy to set up right and are somewhat directional. Very disappointing; not thrilled about j-poles - to say the least. Isolated it from the mast, kept it away from anything that could possibly capacitively de-tune it, and added a choke on it as well. The directional part came as a complete surprise; had no idea that would be a problem since it is a vertical. Hope you have better results than I did.

If I needed to build a 2m vertical, I would build a Vector 4000 scaled down to 2m resonance from scratch. Easier still, a 2m vertically polarized full wave loop. Much cheaper/easier/smaller too . . .

 

[Captain Kilowatt]

Robb if you found the J-pole to be somewhat directional it must have been due to coupling with something else or feedline issues. I have built a couple including an extended J-pole that has another 1/2 wave section fed in phase and stacked on top the main section. It worked VERY well. Any J-poles I have made showed no directionality but were a bit tricky to get a perfect match. The spacing seems to have the most effect when trying to minimize SWR. IMHO the J-pole is an OK antenna for working local repeaters where you do not need a great antenna but then again in that situation a simple 1/4 wave groundplane would likely work just as good. I consider the VHF J-pole and the G5RV as starter antennas for beginners however I rarely recommend them for beginners because I believe there are better antennas to start off with even if they do require a bit more knowledge to understand properly especially for HF.