[RFI] QUESTION

[Gary Johnson]

That’s easy. RF is picked up on the AC lines then enters any nonlinear device plugged into those lines, such as a walk wart. There, RF is rectified, harmonics are generated, and that’s mixed with all the garbage on the power line, then re-radiated via conducted emissions. Many harmonics are normally expected. This is the classic problem for any SO2R or M/M station. 

Case study: At 8P5A, Tom has very little ancillary stuff plugged in and yet he had your problem. He traced it to a single LED light. Once removed, the harmonic garbage disappeared. 

Gary Johnson NA6O  
gwj at wb9jps.com

> On Dec 21, 2020, at 4:06 PM, rfi-request at contesting.com wrote:
> 
> From: David Eckhardt <davearea51a at gmail.com>
> Subject: [RFI] QUESTION
> 
> I'm out of ideas on this one!  Where does the raspy modulation come from
> on the harmonics which changes with position in my radio room on a battery
> operated receiver?
> 
> Situation:
> 
> transmit on 7.010 MHz
> receive on second harmonic, 14.020
> 
> transmitter:  IC-7300
> receiver:  IC-7610
> and reversed
> Demod:  CW or SSB (or AM, for that matter)
> 
> Fundamental sounds clean.  Second harmonic sounds modulated by 120-Hz (and
> a few harmonics of the line) and quite raspy - pretty awful.
> 
> Receiver:  portable battery operated receiver (Grundig G3) with same
> transmitters:  I can walk around the room tuned to the second harmonic and
> find places in the room where things are clean and other positions where
> the second harmonic (and third) sound awful with 120 Hz raspy
> 'modulation'.  Any idea how I can account for this localized behavior?  I'm
> out of theories.
> 
> Dave - W?LEV