J Pole questions
 

Hi Fella's

I have recently built a J pole for 2 meters from the handbook and I was
wondering if any of you had some tuning tips.

Thank you in advance.

Mike Burch K8MB

Apache Junction AZ

Hi Mike

You can place a brass machine screw in the pipe caps for fine tuning.
EG moving the center frequency up and down. (vertical screw)
Changing the impedance slightly (stub screw)
Adjusting the SWR is by moving the coax connect point up or down
slightly.

TTUL
Gary


Mike Burch verbositized:

Hi Fella's

I have recently built a J pole for 2 meters from the handbook and I was
wondering if any of you had some tuning tips.

Thank you in advance.

Mike Burch K8MB

Apache Junction AZ

Mike Burch wrote:

I have recently built a J pole for 2 meters from the handbook and I was
wondering if any of you had some tuning tips.


I just put mine up this past weekend. I made a Jpole out of 3/4 inch
copper pipe. My coax is attached with copper pipe clamps. To tune, I
used a MFJ antenna analyzer, but anything you have that measures SWR
will be okay.

As I moved the clamps up or down on the antenna, I could tune the SWR &
resonance pretty easily. Biggest problem was having to walk away from
the antenna (on the roof) to keep from affecting the readings. Tuned it
for 1:1 on my favorite repeater frequency which happens to be in th
emiddle of the band, and have less than 1.5:1 at the edges. The antenna
works very well compared with the homebrew 1/4 wave ground plane I had
before.

The clamps are supposed to move up and down equally on the antenna, but
the position that gave me the best resonance and SWR hade the braided
wire clamp just a tad below the center conductor clamp, so that may be
another area for adjustment.

Seems like it would be a dead short, doesn't it?

Hope this helps!

- Mike KB3EIA -

Mike Coslo wrote:
Mike Burch wrote:

I have recently built a J pole for 2 meters from the handbook and I
was wondering if any of you had some tuning tips.



I just put mine up this past weekend. I made a Jpole out of 3/4 inch
copper pipe. My coax is attached with copper pipe clamps. To tune, I
used a MFJ antenna analyzer, but anything you have that measures SWR
will be okay.

As I moved the clamps up or down on the antenna, I could tune the SWR &
resonance pretty easily. Biggest problem was having to walk away from
the antenna (on the roof) to keep from affecting the readings. Tuned it
for 1:1 on my favorite repeater frequency which happens to be in th
emiddle of the band, and have less than 1.5:1 at the edges. The antenna
works very well compared with the homebrew 1/4 wave ground plane I had
before.

The clamps are supposed to move up and down equally on the antenna,
but the position that gave me the best resonance and SWR hade the
braided wire clamp just a tad below the center conductor clamp, so that
may be another area for adjustment.


BTW, I have seen some plans for a Jpole identical to the one I built,
and they call for several turns of coax as a balun for the thing. I
really don't think that is needed. I measured out 1.1:1 SWR @ 50 ohms in
the middle, and good SWR across the band.

Then again, maybe there are some hams that put a balun on everything! ;^)

- mike KB3EIA -

BTW, I have seen some plans for a Jpole identical to the one I built,
and they call for several turns of coax as a balun for the thing. I
really don't think that is needed. I measured out 1.1:1 SWR @ 50 ohms in
the middle, and good SWR across the band.


Thats not the reason for the Balun. The balun is to keep the feed line from
radiating

WA8ULX wrote:
BTW, I have seen some plans for a Jpole identical to the one I built,
and they call for several turns of coax as a balun for the thing. I
really don't think that is needed. I measured out 1.1:1 SWR @ 50 ohms in
the middle, and good SWR across the band.



Thats not the reason for the Balun. The balun is to keep the feed line from
radiating

Is it going to radiate when everything is set up correctly?

- mike KB3EIA -

Mike,
Can the feed line radiate if everything is setup
correctly? Yes. Will it radiate? Maybe. Using a
choke at the feed point, or a balun, isn't any trouble,
so why not?
'Doc

Thanks to all of you for you input. It helped me out a lot.

Best wishes.. Happy Thanksgiving

Mike Burch K8MB

Apache Junction AZ