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

[Chris Murray]

I had a crown that emitted 504.9 MHz fifth harmonic of the carrier  
interfering with a TV 19 reception. Not there on the RF output Jack.  
It was radiating from the cabinet.

Chris Murray
KKNU, Eugene, Ore.

Sent from crmurray at clearwire.net I-phone


On Aug 17, 2009, at 7:49 PM, "Phil Alexander, CSRE, AMD" <dynotherm at earthlink.net 
 > wrote:


> 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

>

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