On Sat, 28 Jun 1997, henry gillow-wiles wrote:
> a funny thing....
> i'm the guy w/the th7 that had an odd swr curve on 15m. i rearranged my
> shack tonite and while doing this, checked the swr w/ my mfj meter,
> starting at the remote coax switch.
> finally everything in line. radio, amp, tuner, low pass filter, remote
> switch. nice and flat.
> now the hmmmmm thing. what made the swr funny in the first place? loose
> connector? bad jumper? how can i keep this from happening again?
One way to prevent the problem is to develop a procedure for checking
antenna adjustments without the equipment in the line. This will ensure
that only antenna system elements are involved in any odd readouts and
limit the number of places to check for problems.
Starting with the antenna along, using one of the portable meter and
source instruments (AEA, MFJ, Autek) is ideal, since readings (assuming
the instrument was checked before tower climbing) then indicate antenna
(and possible tower connection) performance alone. Second best is down
the coax a ways, with only the antenna, tower, coax, and antenna frounding
system in the line of testing. Down here, one can check with both the
source/meter instrument and with an independent rig/SWR meter to correlate
results.
Because of the number of instruments in the full station set-up, any guess
as to the source of the false readings would be speculative. But
reinstalling the gear suggests things like poorly seated coax connectors,
poorly seated ground line connections, and the like. Sometimes common
mode paths that throw off SWR meters are sneaky, and coax connector should
be flexed periodically (unscrewed and retightened for thread cleaning and
center conductor pin cleaning). You might be amazed at how little contact
is made between 238s and 259s that have not been moved in years--even
indoors.
But all of that is guess work. The best way to prevent recurrence is the
development of a good antenna test and adjustment procedure to isolate any
problems to the least number of possible components. If that procedure
shows a problem, but reconnecting all the gear says no problem, then you
have 2 problems.
Good luck.
-73-
LB, W4RNL
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|