[BC] Te st your wits on this

[David Senft]

Good Morning to All!
Thanks to all for the excellent clues respecting our BE FM20T issue. I'll
address a number of suggestions made thus far. In answer to Jerry's
suggestion, we have new replacement spare IPA and power supply modules which
essentially gives you a new IPA. Same symptoms. The coax between the IPA and
amplifier was also subbed. No dice. We tried using the Bext 300 as an IPA,
-same results. It appears to be the main PA without doubt. Richard's
suggestion appears to be the closest to what may be the problem although
replacement of the filament contact ring is a "no brainer". The socket has
built-in bypassing that is essentially a copper-faced kapton sheet that is
clamped into place. The Harris 25K uses a similar product for the screen
bypass. Replacement of the socket ring simply requires un-bolting 6 bolts
and dropping in a new ring. 15 min. work. As a precaution, we have a
complete new socket on Fed Ex today. Mike's on the right track as it is
indeed a spur that appears out of the band-pass of the combiner that is
reflected back into the PA amplifier and the resulting VSWR shuts the thing
down. As start-up of any transmitter will generate some "hash", it appears
that it doesn't take much to set this one off. While we've never had to
neutralize one of these transmitters, this will be our next step. Tom's idea
of running it directly into the antenna is workable aside from the fact that
this installation has two broadcasters on the same antenna. We'd have to
shut the competitor off to test, -not always a bad idea :). As the antenna
load is more broadband, it would likely work. Warren's suggestion about the
transfer switch is valid, -have seen this too many times but the transfer in
this case is a simple U link patch. We've examined and swept every inch of
the transmission lines in the plant so we are confident that it isn't a
hardware issue. Our standby is a full-power off-site installation. I'll keep
you posted.