Have you tried a analyzer at the matching device? Perhaps you have a corroded
ground that looks OK at DC but not RF. While you are looking at the analyzer
you can move and shake the parts. (of course, see if there was a change after
you remove you hand or tighten a nut.)
Are you sure your PL-259 at the end of the coax is good? How did you check
your transmission line? With a dummy load connected to the PL-259? Just a
wild guess, but I would really suspect the shield solder connection to the
PL-259.
Good Luck.
Mike
AD6AA
--- On Mon, 12/29/08, Kim Elmore <cw_de_n5op@sbcglobal.net> wrote:
> From: Kim Elmore <cw_de_n5op@sbcglobal.net>
> Subject: [TowerTalk] Now this is maddening...
> To: towertalk@contesting.com
> Date: Monday, December 29, 2008, 2:23 PM
> I've been shunt-feeding my tower for awhile now using an
> L-network
> and a motor-drive to adjust a vacuum variable. Until
> recently, all
> has been just hunky-dory. However, last night it appeared
> that my
> motor drive no longer worked as I couldn't adjust the
> match. What's
> more, the match started to act flaky, with variations that
> appeared
> to act randomly.
>
> Today I opened up the box that holds the matching network
> and found
> that there was some water inside and that the nuts holding
> the SO-239
> connectors had corroded on the inside. Water had deposited
> some dirt
> and detritus on the inside of the SO-239 and it was wet.
> So, I
> cleaned everything out with alcohol (91% isopropyl).
>
> Found the motor drive was a bit cranky, so I lubed it up
> and assured
> my self that it worked as it was supposed to. But, no
> matter how I
> adjust things, I no longer can get a match. I checked the
> vacuum
> variable and it appears ok -- the mechanism works and all
> and it's
> not shorted. All the wiring is intact. The shunt is still
> connected,
> the grounds good, the antennas up top still work and are
> intact, etc.
> The capacitor that's in there is a 5-500 pF, so as a
> sanity check I
> substituted in a 7-1000 pF that I have laying around. Still
> no match
> can be found. The transmission line checks good, so
> that's not it, either.
>
> Anybody else ever seen this? What have I missed?
>
> Kim Elmore, N5OP
>
> _______________________________________________
>
>
>
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