[SBE] FW: Question about a Crown exciter and transmitter, over temperature, and spurious signals

[Mike Langner]

Hello everyone !


I'm about to try to "fix" a problem on a site where an FM transmitter
operating at about 1 kW power output and about 1 kW erp may be causing
interference to some VHF Public Safety equipment at a remote mountaintop
site.

Access to the site in wintertime is an arduous snowshoe/snowcat trip, so
nobody involved in the problem has been there in wintertime when the problem
occurs.

Summertime presents no interference.

My suspicion is that the FM transmitter building (a typical tiny mountaintop
building) overheats in winter from snow pack into the marginally designed
airflow/vending, and the equipment overheats.

The equipment in question is a Crown FM 100 exciter operating at about 60
watts, and a Crown FM2000A transmitter operating at 1050 watts.

The system employs a Shively 2604-3A bandpass cavity filter in the output.
The radio station owner voluntarily purchased and installed the filter as a
goodwill gesture and to attempt to stop any spurious signals from getting to
the antenna.

My sense without going up the mountain (I was there once a number of years
ago) that the Crown equipment is overheating, generating spurious signals
that may be emitted through the cabinet or by inter-chassis wiring.

I have gotten reports that the building is "hot" in wintertime.

Does anyone have any experience with "hot" Crown exciters or transmitters
getting "squirrelly?"

Seems to me that I repaired a 100 watt Crown amplifier some years ago which
exhibited exactly this problem.

Your thoughts?


Thanks!

Mike/

Mike Langner, CPBE
929 Alameda Road NW
Albuquerque, NM 87114-1901

(505) 898-3212
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://seven.pairlist.net/pipermail/sbe/attachments/20090817/de1b0b45/attachment.html>