[RFI] receiver spurious response

Cortland Richmond ka5s@earthlink.net
Wed, 13 Mar 2002 10:59:2 -0800

By all means do check for a spur. Is your TX synthesized? How clean is the
PLL? For that matter, how clean is HIS handheld's synthesizer? 
But it could be an IM problem. Has a new user moved in on your tower, at
453.4? Is there one in HIS area at 446.4? What do the 3rd order numbers
look like for sources local to his area?
A less innocent possibility is, someone retransmitting your link. This
happened up here, a malicious operator retransmitting one of the local
repeaters on another county's law enforcement frequency. 

P.S.: I hear you guys fine up here in Sonoma County, nights.

> [Original Message]
> From: Tony Dinkel <tonydinkel@clubnet.net>
> To: <rfi@contesting.com>
 > Date: 3/13/2002 10:24:17 AM
> Subject: [RFI] receiver spurious response
> 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
> level.
> =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
> issue.
> 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.
> Anybody?
> tony dinkel
> wb6mie
> kfi am 640, more stimulating talk radio; klac 570, not just facts,=20
> feelings;  kxta fox sports 1150
> http://www.tonydinkel.dynip.com/