Mysterious Signal

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Does anyone recognize this? The fundamental is about 269 kHz and the harmonics extend up well beyond 4 MHz. First noticed it as S9 interference on 160M at about 1.891 MHz. 
Sometimes it is on, sometimes it is not. Doesn't correlate to sunrise/sunset or anything else I can identify yet. Loudest on ground mounted receive antenna, not present when using dummy load.



Screen shots from Flex 6700.

73 John N5CQ

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John Langdon

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Posted 1 month ago

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Joe N3HEE

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What does it sound like ?
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John Langdon

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Sounds like video on an AM detector, but the sidebands are constant. The center frequency drifts a bit, but not much.
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Joe N3HEE

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Can you make a audio recording and send it to me ?
(Edited)
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Stan - VA7NF

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These are normally with a switching power supply base and can go from small power buck to grow-op digital ballast multi KW switches.  If you really zoom in with your 6700, you will likely see the sidebands are 60Hz or 120Hz based. 
 I have also seen this from a power drill battery charger or any variable speed motor (i.e. refrigerator compressor, washing machine, pond pump, furnace fan or a/c compressor).  Pick the fundamental or harmonic and go on a DFing fox hunt; Alternately put your 6700 on battery (including switch and monitor/Maestro) and turn off the house power.
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Pat - WH6HI

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Yes, do as Stan recommends . Most likely a switching supply . Going to battery will help see if the noise is in your house or a neighbor. If it is a neighbor, good luck.
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John Langdon

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Seems to be coming in over the power line. Sometimes it shifts center frequency a few kHz. Sometimes it is not there at all.

Brief recording at https://jlangdon18.wixsite.com/n5cq-swap/mystery-noise 

Next step is 'sniffing' with a portable receiver. 

73 John N5CQ

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Pat - WH6HI

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Switching PS WILL drift as the RC circuitry is not that stable.