[RFI] heterodyne on 17 meters

Jim Brown jim at audiosystemsgroup.com
Mon Jul 15 11:48:29 EDT 2013

On 7/15/2013 7:33 AM, Stephen Reichlyn wrote:
> I am hearing an s-3/4 heterodyne on 17m every 18 kHz. Any suggestion 
> of  the source? 

Sure -- if the carriers drift around slightly, the most likely culprit 
is some sort of switching power supply.  If they are very stable in 
frequency, they are more likely to be the clock for a microprocessor.  
Power supplies include wall warts of all sorts, battery chargers, and 
even those built into equipment.

Start with your own home first. Run your radio from a battery, turn off 
any UPS that may be protecting a computer, and kill power at the main 
breaker. If the interference goes away, it's in your house. Then turn 
breakers on, one at a time, to notice when the QRM returns.  But wait a 
while after each breaker, because if it's a switching power supply, it 
will drift in frequency quite a bit as it warms up. You could also 
reverse the process, by restoring power, letting the culprit warm up, 
then turning breakers OFF one at a time.

For a lot more on RFI, see http://k9yc.com/RFI-Ham.pdf

73, Jim K9YC

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