[RFI] 9Khz spacing of intermodes carriers interference

[Jim Brown]

On 1/23/2013 10:16 AM, N1BUG wrote:
> Are you sure, Jim? He said he has carriers every 9 kHz. This is a well 
> known problem from AM BC mixes in Europe, where their MW BC stations 
> are spaced 9 kHz apart. I may be wrong but I believe the 9 kHz spacing 
> is used in the middle east also. What he is experiencing may be the 
> same issue many us in North America have on 1810, 20, 30, 40, ... due 
> to mixes or harmonics from our MW BC stations spaced 10 kHz. 

Based on his second description (hearing audio modulation on those 9 kHz 
spaced signals), I think you're right that they may be coming from some 
sort of broadcast intermod. After hearing that second description, I was 
hoping someone might have some direct experience with it.  In Chicago, I 
heard a FEW mixes on 10 kHz increments, the result of a FEW sources, but 
not a LOT (the result of MANY sources).

Another clue -- if those are broadcast sources, there will be very 
strong carriers that are frequency-stable and quite precisely on 9 kHz 
increments (or 10 kHz in North America).

The symptom of EVERY 9 kHz suggests something in his setup may be 
strongly non-linear, like a preamp or RX front end that's getting badly 
overloaded, or that has poor strong signal performance.

73, Jim K9YC