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@wb9jps.com
On Dec 21, 2020, at 4:06 PM, rfi-request@contesting.com wrote:
From: David Eckhardt <davearea51a@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@sdellington.us
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