[RFI] receiver spurious response

Tony Dinkel tonydinkel@clubnet.net
Wed, 13 Mar 2002 10:24:17 -0800

Hello to the list, I enjoy very much reading the problems and=20
responses that come through here.  I have solved quite a few=20
interference problems myself both professionally and on an amateur=20

=46irst some background...I am a broadcast engineer for KFI AM 640 in=20
Los Angeles.  Since we are "talk radio" we operate in 10 second audio=20
delay to our main transmitter for obscene language deletion and=20
liability issues.  This makes it impossible to receive at a remote=20
site or in our traffic reporter's aircraft over the air.  So, I put=20
up a transmitter on 450.725 mHz that puts our audio signal out in=20
"pre-delay" 24 x 7.  We are licensed for 55 watts tpo and around 800=20
watts erp on Mt. Wilson.

Here is the problem...I got a call from a ham 80 miles away that=20
claims he is hearing my 450.725 transmitter on 448.060 mHz.  Its not=20
a mix, its just there all the time.  He is using a Premier PR-460=20
hand held and we are coming in strong.  That is a frequency=20
difference of 2.665 mHz.  I did some research and determined that the=20
radio uses a 21.4 - 455 IF.  To me, this does not make any sense.

Of course I will check my 450 transmitter just to make sure I have=20
not developed a spur with more power than my center channel.  I can't=20
imagine I have because there are enough hams in LA who know me well=20
enough to let me know of problems like this before it would become a=20

My question is...has anyone had any experience with this or any other=20
radio and a possible off channel response?  I seem to recall my VX-5R=20
(before I lost it) had a similar response around =B1100kHz or so.  Does=20
anyone know what this could be caused by?  I am considering injection=20
spurs out of the synthesizer as the only possibility.


tony dinkel
kfi am 640, more stimulating talk radio; klac 570, not just facts,=20
feelings;  kxta fox sports 1150

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