[RFI] QUESTION

[donovanf at erols.com]

Hi Gary, 


The process for identifying this type of RFI is the same as for any other RFI, 
except you need to use your transmitter to excite the RFI generating source. 



First verify that the RFI is not coming from your own home 


- kill all of the circuit breakers in your home and power up ONLY 
your transmitter. All accessories should be DISCONNECTED from 
AC power. You may need to use your amplifier to produce 
enough RF to trigger raspy harmonics from RFI generating source. 


- Put your transmitter on the air, keying it from a memory keyer 
is a good approach 

- if the raspy harmonics have gone away, start turning on the 
circuit breakers in your home, one by one, until the raspy harmonics 
reappear. 


If you determine that the RFI is not being generated in your own home, 
turn your directive antenna in the direction that produces the strongest 
raspy harmonics. A sensitive spectrum display such as the Elecraft P3 
helps immensely. 


Then use a portable receiver to hunt for the RFI source along the line 
of bearing identified by the previous step. 


Good luck 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Gary Johnson" <gwj at wb9jps.com> 
To: rfi at contesting.com 
Sent: Tuesday, December 22, 2020 12:48:16 AM 
Subject: [RFI] QUESTION 

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 

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