[TowerTalk] 40m Beam: Problem - Attenuation and Static

[john at kk9a.com]

It sounds like a bad connection, a little RF causes it to temporarily
reconnect. The easiest way to locate the problem is to start bypassing
things when in failure mode until the RX signal returns. If you have an
amplifier I would start there as bad T/R relays are common.

GL
John KK9A



Richard Thorne N5ZC

I've had a strange problem develop with my JK 404C 4 element tribander.

  - The signal is sometimes attenuated.  Per my Flex 6600, I'll show a 
noise floor of -130db, when I transmit a bit the noise floor increases 
to -120db.

- After transmitting and the noise floor increases, I get a lot of broad 
band static, which appears to be random and comes and goes.

- The SWR on the antenna is excellent and doesn't change, which seems to 
be strange with symptoms described above.

- I'm using a 2 antenna WX0B stack match to combine the JK404c and a F12 
2 element delta 240 40m yagi.  I have absolutely no issues with the F12 
delta 240 going through the same feed line (from the stack match) to the 
transceiver when the Delta 240 is the only antenna selected on the stack 
match.

Here's what I've done to attempt trouble shoot the problem:

- disconnected the JK 404C feedline from the stack match and attached an 
Elecraft KX2 directly to the feed line.  Same issues as described above.

The feed line is LMR-600 from outside the shack to the tower.  The coax 
is direct buried, no pvc pipe.

- From the shack to the base of the tower a run of LMR-600 about 195' 
long.  RG-213 from the LMR-600 via SO-239 / female N adapters to another 
length of LMR-600 (with the same adapters)

- The LMR-600 goes from the base of the tower up to the where the 
antenna is mounted.  The LMR-600 is attached to the tower leg inside the 
tower, not outside.

- RG-213 jumper from the LMR-600 to the balun/feed point of the 
antenna.  At this junction I'm using a DXEngineering grounding block 
with a 2" barrel so-239.

All that being said has anyone come across the same symptoms of an 
attenuated signal and static that was caused by coax adapters, bad coax 
or a balun at the feed point?

This particular antenna has a phasing line between two driven elements 
with 1:1 current baluns at each feed point.

I'm stumped at this point.  I climbed the tower this morning and didn't 
see any obvious mechanical issues.

Any ideas or other things to check?

Thanks in advance.

Rich - N5ZC