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

[Phil Alexander, CSRE, AMD]

Having been through an overheat problem at sub-sero outdoor ambient,
a couple of things come to mind. Installing indoor and outdoor temp
sensors on the remote control will help understand the scope of the
problem. Second, consider installing a powered louver ventilator and
exhaust fan with remote control. That should get you through the 
winter and let you prove at temperature relationship aspect.
If that is proven, a Baird or similar HVAC unit may be the final
answer.

Phil Alexander, CSRE, AMD


-----Original Message-----

>From: Mike Langner <mlangner at swcp.com>

>Sent: Aug 17, 2009 7:12 PM

>To: sbe member discussion mail list <sbe at sbe.org>

>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