[RFI] QUESTION

[K9MA]

I saw something like this when I was testing a QRP transceiver, 
listening via the main antenna on the K3/P3. Even on the fundamental, it 
looked like there was all sorts of hash, sidebands, etc. It wasn't 
"real". The proper way to do such a test is with a high power dummy 
load/attenuator between the transmitter and receiver. That eliminates 
the possibility of external mixing and harmonic generation. A 
jury-rigged dummy load and a capacitive divider would work, if you're 
careful. Or just two dummy loads close together.

73,

Scott K9MA


On 12/21/2020 6:48 PM, Gary Johnson wrote:
> 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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-- 
Scott  K9MA

k9ma at sdellington.us