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[Solved] Need Help with open stub jpole antenna

Nov 19th 2020, 19:41

KE8PSV

Joined: Oct 17th 2020, 12:52
Total Topics: 0
Total Posts: 0
I have an open stub jpole antenna (2m/70cm) connected via 100 feet of RG8X cable. Reception is great, but transmission is terrible. In fact, when hooked up to my VHF amplifier (Btech AMP-V25), the amplifier has a fast clicking noise synced to the flashing TX light and also sounds an alarm. I am guessing this is an SWR alarm? The antenna is completely within specs, so I just don't get it. I have tested a short RG58 cable to the same effect. I have tried looping cable for balun and without, also to the same effect. I have checked and there are no shorts from the antenna through the cable. Any ideas?
Nov 20th 2020, 06:16

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
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I looked and couldn't find a manual to explain how the SWR protection works. I'd suggest getting an SWR meter or analyzer to help sort things out. Another possibility is over-driving the amp. I don't know enough to rule that out.

It is possible there could be an issue with the automatic PTT circuitry.

If you can't come up with a way to measure SWR you may want to experiment with a horizontally polarized half wave dipole in the clear or a dummy load to figure out exactly what the amplifier is doing.

Zak W1VT
ARRL Senior Lab Engineer
Nov 20th 2020, 06:52

KE8PSV

Joined: Oct 17th 2020, 12:52
Total Topics: 0
Total Posts: 0
The amp works fine with my mag mount Nagoya antenna. BTECH confirmed that the amp is acting in accordance with SWR that is too high or improper grounding. My SWR meter shows infinite SWR. Again the antenna is within spec, and there are no shorts.
Nov 21st 2020, 10:17

WA0CBW

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
What results do you get if you put a dummy load at the antenna end of the coax?
Bill
Nov 29th 2020, 21:33

KE8PSV

Joined: Oct 17th 2020, 12:52
Total Topics: 0
Total Posts: 0
Turns out my power supply was the issue. Switched out the power supply and the amplifier worked like a charm. In the meantime, I made a ground plane antenna and it well outperforms the open stub jpole antenna, at least in the attic. I was able to hit a lot more repeaters with it at further distances.

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