[RFI] Inter-station interference question.

donovanf at starpower.net donovanf at starpower.net
Thu Nov 21 13:06:33 EST 2019

"Yes the harmonic DOES have a growl to it!" 

Hi Martin, 

You've described a classic symptom of an intermod problem, which 
I refer to more specifically as "RF flooding." No amount of filtering 
of your transmitted or received RF signals will fix it. In most cases 
the intermod originates in your own ham shack, in your home or in 
nearby homes or buildings. 

It results from a very strong RF signal entering an electrical or 
electronic device with little or no protection from a very strong RF 
signal. When the RF enters the device it mixes with AC power or 
digital signals and re-radiates both the fundamental and harmonics 
of the very strong RF signal onto the AC power wiring which serves 
as an antenna, but the reradiated signal is modulated by 50 or 60 Hz 
AC power and its harmonics or by digital signals (these are the 
sources of the "growl" you reported). 

The RFI hunting process is nearly identical to hunting any other 
RFI problem. Turn your transmitting antenna to the direction 
that causes the most "growl." Then turn your receiving antenna 
or RFI hunting antenna to maximize the "growl." Then hunt the 
RFI the same way you do for AC power line RFI. 

Start by turning off all AC power in your home except for your 
transmitter and receiver. All other equipment in your shack and 
your home -- especially all UPSs and wall warts -- must be turned 
off and all wall warts unplugged. 

Good luck! 


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