[RFI] AM Radio Interference On 75 meters

[Cortland Richmond]

Joe,

It's not a multiple of the distant broadcaster.. Note what Dave said 
about mixing. Here are Reno AM stations
from http://en.wikipedia.org/wiki/List_of_radio_stations_in_Nevada:

	
	
	
	
KHIT <http://en.wikipedia.org/wiki/KHIT> 	1450 AM 	Reno 	Lotus Radio 
Corp. 	Sports
KIHM <http://en.wikipedia.org/wiki/KIHM> 	920 AM 	Reno 	IHR Educational 
Broadcasting 	Religious
KJFK <http://en.wikipedia.org/wiki/KJFK> 	1230 AM 	Reno 	Americom Las 
Vegas Limited Partnership 	Talk/Personality
KKOH <http://en.wikipedia.org/wiki/KKOH> 	780 AM 	Reno 	Radio License 
Holding CBC, LLC 	News Talk Information

	
	
	
	

	
	
	
	
KPLY <http://en.wikipedia.org/wiki/KPLY> 	630 AM 	Reno 	Lotus Radio 
Corp. 	Sports

	
	
	
	

	
	
	
	

	
	
	
	
KXEQ <http://en.wikipedia.org/wiki/KXEQ> 	1340 AM 	Reno 	Azteca 
Broadcasting Corporation 	Regional Mexican
KXTO <http://en.wikipedia.org/wiki/KXTO> 	1550 AM 	Reno 	First 
Broadcasting of Nevada, Inc. 	Latin Contemporary

blanks are deleted FM stations

I'll assume your victim is near a local AM transmitter. Try an AMBC 
highpass filter in front of the victim radio,
as both harmonics generated in the RF stage or mixer AND mixing products 
of combinations of local high power
stations in a rigs' mixer can quite easily beat with a normally strong 
though more distant station with effects you describe.

If it doesn't help, you may be seeing IM generated at the local 
transmitter site (there may be collocated antennas or even a shared 
antenna) mixing with the Sacramento station.

Also, see if you can make out modulation that correspons with signals 
you hear from your local stations.

I don't have an IM calculator on the computer, and one I found doesn't 
seem to like my display,  but poke around
on the net and you may find one.

Oh, and cut power to any cable or other broadband. In fact... turn off 
ANYTHING that might be generating a carrier locally. Especially if it's 
on a timer.  You might be surprised what dwells in, well, dwellings.

Good luck,

Cortland
KA5S

On 9/18/2012 1315, Joe wrote:
> ----- Original Message -----
> From: "David Robbins" <k1ttt at verizon.net>
> Subject: Re: [RFI] AM Radio Interference On 75 meters
>
>
>> 3960khz is not a harmonic of 1530khz so something else is also happening here.  listen carefully to the kfbk signal and see if there is some other signal mixing with it.  check for other harmonics and other signals that it might be mixing with to end up on 3960...
>>
>> 1530 + 2430khz?
>> 1530*2 + 900khz?
>> 1530*3 - 630khz?
>> 1530 + 2*1215khz?
>> 5490 - 1530khz?
>> etc, etc.
>>
>>