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

[Don Moman VE6JY]

Have certainly seen similar things here.... likely a coax connector not
quite tight or has oxidation - but usually a small dose of transmitted RF
will break thru the oxidation layer and make it work again for a while.
But as the connection is still pretty tenuous at best, one can get noise
generated there. I have seen it in the form of AM BCB rectification and the
resulting IMD stuff.

73 Don
VE6JY

On Sun, Mar 17, 2019 at 8:00 PM Richard Thorne <rthorne at 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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