[RFI] QUESTION

[Dave Cole]

I have a handy flow chart for location of RFI at:

https://www.nk7z.net/i-have-rfi-now-what-locating-it/

Plus a few hints on location of RFI at the same URL.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 12/22/20 1:53 PM, donovanf at erols.com wrote:
> 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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