J-Pole Problem: Great at Low Pwr, No-Go at High Pwr
 

I have a rather odd problem with a J-Pole "copper cactus" antenna that I
just installed this evening. I can transmit and hit local repeaters w/o
any problems w/ an HT on LOW power ( 1.5W) but can't bring up even the
closest repeater on HIGH power (4.5W).

The SWR for the antenna is 1.1:1 to 1.3:1 across the entire 2m band
(direct antenna reading - not w/ the transmitter in the loop) and I've
got a 5-coil balun right at the feedpoint to trap any return RF.

Any suggestions? It wasn't my intention to build a QRP rig.... ;)

Perplexedly,
Scott Drumm
N3XFD

I recently had a problem with my HF antenna on one band that I fixed today.
It would shut down the powersupply (trip the earth leakage protection) when
the power out of the TX went over about 70W on 40 metres (not the other
bands). The antenna was a 40m/20m parallel dipole.

It ended up that the antenna was shorting to ground at that power from the
high voltage parts (end of the 40m dipole). I cleared it and it now works.

A similar situation may be happening with you. The antenna may be shorting
out at higher powers. Check the materials you used and the spacngs at the
high voltage sections of the antenna. Check the SWR at both the low power
setting and at the high power setting. Also actually check the transmitter
output power at both those settings. If the SWR goes high or the TX power
out goes low when the high power is selected this would indicate a short of
some kind at those setings.

"Scott Drumm" wrote in message
...
I have a rather odd problem with a J-Pole "copper cactus" antenna that I
just installed this evening. I can transmit and hit local repeaters w/o
any problems w/ an HT on LOW power ( 1.5W) but can't bring up even the
closest repeater on HIGH power (4.5W).

The SWR for the antenna is 1.1:1 to 1.3:1 across the entire 2m band
(direct antenna reading - not w/ the transmitter in the loop) and I've
got a 5-coil balun right at the feedpoint to trap any return RF.

Any suggestions? It wasn't my intention to build a QRP rig.... ;)

Perplexedly,
Scott Drumm
N3XFD

On Sun, 12 Oct 2003 04:02:45 GMT, Scott Drumm
wrote:

I have a rather odd problem with a J-Pole "copper cactus" antenna that I
just installed this evening. I can transmit and hit local repeaters w/o
any problems w/ an HT on LOW power ( 1.5W) but can't bring up even the
closest repeater on HIGH power (4.5W).

The SWR for the antenna is 1.1:1 to 1.3:1 across the entire 2m band
(direct antenna reading - not w/ the transmitter in the loop) and I've
got a 5-coil balun right at the feedpoint to trap any return RF.

With the transmitter in the loop, try measuring forward and reverse
power at both power levels, low and high.

Bob
k5qwg


Any suggestions? It wasn't my intention to build a QRP rig.... ;)

Perplexedly,
Scott Drumm
N3XFD