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

[Vik Persaud]

On the Crown Exciter I remember there was a driver board on the underside of the Exciter which would cause the problems you speak of. Change the FET, resistor and Capacitor. The original FET used had some issues. The Crown Tech would tell you the Part No. for the replacement FET. You can also purchase a new driver board from Crown. The clue is the resistor. If the FET is defective you will see on the resistor signs of it over heating.
Kishore Persaud, CSRE, CBNT



From: Mike Langner 
Sent: Monday, August 17, 2009 7:12 PM
To: sbe member discussion mail list 
Subject: [SBE] FW: Question about a Crown exciter and transmitter,over temperature, and spurious signals


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



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