OK, I have a new 2 meter j-pole antenna installed in my 3rd floor
attic. I have 50 feet of LMR240 coax running to the basement. I
measure SWR at the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?

Thanks for any insight, jimbo

jimbo wrote:

OK, I have a new 2 meter j-pole antenna installed in my 3rd floor attic.
I have 50 feet of LMR240 coax running to the basement. I measure SWR at
the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter band?

That's what I would conclude from the data given. Wind some
wire around the tip top and extend the antenna by a few
inches. Then repeat your SWR measurements.
--
73, Cecil http://www.qsl.net/w5dxp

"Cecil Moore" wrote in message
om...
jimbo wrote:

OK, I have a new 2 meter j-pole antenna installed in my 3rd floor attic.
I have 50 feet of LMR240 coax running to the basement. I measure SWR at
the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?

That's what I would conclude from the data given. Wind some
wire around the tip top and extend the antenna by a few
inches. Then repeat your SWR measurements.
--
73, Cecil

One might also try adjusting the feed point location and see what effect
that has.

Harold
KD5SAK

kd5sak wrote:
"Cecil Moore" wrote in message
Wind some
wire around the tip top and extend the antenna by a few
inches. Then repeat your SWR measurements.

One might also try adjusting the feed point location and see what effect
that has.

That would be good to do after adjusting the length.
--
73, Cecil http://www.qsl.net/w5dxp

kd5sak wrote:
"Cecil Moore" wrote in message
om...

jimbo wrote:


OK, I have a new 2 meter j-pole antenna installed in my 3rd floor attic.
I have 50 feet of LMR240 coax running to the basement. I measure SWR at
the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?

That's what I would conclude from the data given. Wind some
wire around the tip top and extend the antenna by a few
inches. Then repeat your SWR measurements.
--
73, Cecil


One might also try adjusting the feed point location and see what effect
that has.

Harold
KD5SAK



I have done that on a j-pole that I made, but that antenna was in my
shack, where it was accessible. This antenna is in a third floor attic
where I have to wriggle my feet through 14 inches of insulation to
find a rafter to stand on. Not conducive to much tweaking.

Thanks, jimbo

Cecil Moore wrote:
jimbo wrote:

OK, I have a new 2 meter j-pole antenna installed in my 3rd floor
attic. I have 50 feet of LMR240 coax running to the basement. I
measure SWR at the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?


That's what I would conclude from the data given. Wind some
wire around the tip top and extend the antenna by a few
inches. Then repeat your SWR measurements.

I am not sure what you mean by "wrap some wire around the tip top." I
could splice some wire on the long leg of the ladder line?

jimbo wrote:
I am not sure what you mean by "wrap some wire around the tip top." I
could splice some wire on the long leg of the ladder line?

The antenna appears to be too short. Lengthen the antenna,
normally accomplished at the tip top.
--
73, Cecil http://www.qsl.net/w5dxp

On Mon, 20 Mar 2006 08:12:51 -0700, jimbo wrote:

OK, I have a new 2 meter j-pole antenna installed in my 3rd floor
attic. I have 50 feet of LMR240 coax running to the basement. I
measure SWR at the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?


Have you a common mode choke on the feedline? J-poles are nortorious
for feedline common mode problems.

Danny, K6MHE

Dan Richardson k6mheatadelphia wrote:
On Mon, 20 Mar 2006 08:12:51 -0700, jimbo wrote:


OK, I have a new 2 meter j-pole antenna installed in my 3rd floor
attic. I have 50 feet of LMR240 coax running to the basement. I
measure SWR at the following frequencies on simplex.

144.2 2.5
145.2 2.4
146.2 2.3
147.2 1.9
147.9 1.7

Can I conclude that the antenna is electrically short for the 2 meter
band?



Have you a common mode choke on the feedline? J-poles are nortorious
for feedline common mode problems.

Danny, K6MHE


Maybe a 4-5 loop coil of coax close to the feed point?

Thanks, jimbo

On Mon, 20 Mar 2006 15:01:53 -0700, jimbo wrote:

Dan Richardson k6mheatadelphia wrote:


Have you a common mode choke on the feedline? J-poles are nortorious
for feedline common mode problems.

Danny, K6MHE


Maybe a 4-5 loop coil of coax close to the feed point?

Thanks, jimbo

Yes, that would help.

Danny