Copper J-Pole build for UHF / GMRS

[conve36]

This is my first home built J-Pole for GMRS.

Can anyone give me any tips or tricks on it? Mounting? Balun?

I have the feed point 1.5cm up from the ground point and 1.5cm space between the stub and main element.

Does it need a specific length of coax? Mount to a metal pole OK? Thanks!

 

[kb9hgi]

Oh my no pl259 on the end of that coax? Is the coax just taped to your so239?

 

[gewecke]

YES!!!! You definitely NEED a teflon PL 259 on the end of that feedline which will plug in to the SO 239 you have soldered on! I mounted my so 239 on a plate for added strength,but other wise your J pole should do fine. ALSO make sure your PL 259 is installed on the cable correctly. I did not see your center conductor even exposed in that cable,and bear in mind that the shield is your ground for the antenna,
N9ZAS

 

[n5usr]

Have you checked SWR? It's been a long time since I built a UHF J-pole (for the ham band) and it's in the attic so can't go look at it, but IIRC the feed point on mine is higher than that. I'm almost positive it wasn't that close to the bottom of the J.

I didn't solder my feed connections, I used stainless steel hose clamps so I could slide the connections up/down to adjust SWR. I suppose at that point if you wanted you could solder. I just goop the hose clamps and end of the coax up with sealant to keep water out.

Which brings up the next point, on yours I would suggest gooping the backside of that SO239 (or otherwise sealing it) as well as the PL259 connector or you will wind up with water running down into your coax over time. -- That is, if you intend to put the antenna outside, of course.

Looks nice! I like my "copper cactuses" (cactii?), have one on UHF, a couple on VHF, and even made a monster one for 6 meters!

 

[conve36]

Oh my no pl259 on the end of that coax? Is the coax just taped to your so239?

Actually in the firsts couple pictures I just TEMPORARILY zip tied the connections, but in the rest of the pics I actually soldered the 9913 cable to the so-239 chassis mount (which is of course soldered).

I had a hell of a time soldering the chassis mount so-239 to the copper pipe, actually melted the too much for my liking and plan on replacing it...

I built a similar j-pole from these designs...

Mecworks » GMRS J-Pole Antenna

And it seemed to work better than this copper pipe j-pole... But these things seem to be very touchy... Gonna take some more messing around with I think...

By the way, I am brand new to the hobby. I dont even have my HAM license yet (which I want to get, but dont really know what to study). I started with scanning, then GMRS (WQJZ848 call-sign) and seem to be moving towards amateur now... Thanks for the help and comments!!!

 

[mrweather]

I've built a few copper j-poles over the years. All worked well. Had the most fun putting together the 6m one! I've currently got a 2m/70cm dual-band model in the attic as a backup antenna.

The antenna can be mounted to any kind of mast since the bottom portion (part sticking down from the "U") is at ground potential anyway.

 

[rvictor]

Actually in the firsts couple pictures I just TEMPORARILY zip tied the connections, but in the rest of the pics I actually soldered the 9913 cable to the so-239 chassis mount (which is of course soldered).

I had a hell of a time soldering the chassis mount so-239 to the copper pipe, actually melted the too much for my liking and plan on replacing it...

I built a similar j-pole from these designs...

Mecworks » GMRS J-Pole Antenna

And it seemed to work better than this copper pipe j-pole... But these things seem to be very touchy... Gonna take some more messing around with I think...

By the way, I am brand new to the hobby. I dont even have my HAM license yet (which I want to get, but dont really know what to study). I started with scanning, then GMRS (WQJZ848 call-sign) and seem to be moving towards amateur now... Thanks for the help and comments!!!

So you soldered the center conductor of the coax to the center of the SO-239 and the shield to the outside of the SO-239? While I guess that's possible, it seems like a real opportunity to melt enough of the insulation in the connector and end up with either a short or an open.

Dick

 

[conve36]

So you soldered the center conductor of the coax to the center of the SO-239 and the shield to the outside of the SO-239? While I guess that's possible, it seems like a real opportunity to melt enough of the insulation in the connector and end up with either a short or an open.

Dick

I am in the middle of replacing the SO-239... Does anyone have the exact dimensions of what this antenna's lengths should be for 467.xxx gmrs freqs?

 

[rvictor]

I am in the middle of replacing the SO-239... Does anyone have the exact dimensions of what this antenna's lengths should be for 467.xxx gmrs freqs?

I suggest that once you've done that, you put a PL-259 on the coax rather than soldering it to the SO-239.

Dick

 

[Mikejo]

Have a general question about J-pole antennas.

A while back, I build a 2 meter J-pole for indoors to use while scanning Rail Road frequencies.

When I built it, I did not use a "T" joint connector in order to eliminate the extension for mounting, it turns out it looks exactly like the letter "J".

I have a hook in the ceiling in my apartment from which I hang it, what I am wondering is, will it work better if I get this short section up higher meaning what if I hang it upside down? Will it work better because I got the 17.5 inch section a few feet higher?

 

[Mikejo]

I am in the middle of replacing the SO-239... Does anyone have the exact dimensions of what this antenna's lengths should be for 467.xxx gmrs freqs?

Just google "online J-pole calculator" they ask you to insert the frequency you would like, and then it gives you the dimensions you need for each component.

 

[majoco]

When I built it, I did not use a "T" joint connector in order to eliminate the extension for mounting, it turns out it looks exactly like the letter "J".

...and that;s exactly how it's supposed to be built - whoever decided to add that extra stub out of the bottom got it wrong.
Read.....
https://en.wikipedia.org/wiki/J-pole_antenna
...especially the section on "Mounting".