Rich, I would check the connectors on your feedline run. Sometimes a
connection running RF is made but on RX the connection opens to the point
that the induced noise appears. The same could be true with any loose
nuts/bolts on the feed portion.
Just a thought.
Herb Schoenbohm, KV4FZ
On Sun, Mar 17, 2019 at 5:00 PM Richard Thorne <rthorne@rthorne.net> wrote:
> 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
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