Mystery 'drifting' signal

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Tom41
Posts: 7
Joined: Sun Dec 30, 2018 8:23 pm

Mystery 'drifting' signal

Post by Tom41 » Fri Jan 11, 2019 4:23 pm

I was looking around the Air band at approx 132MHz on my SDR, and came across this mystery signal. It's constantly changing frequency, then every 1.5 seconds jumps to another frequency making it impossible to tune in clearly. I'm wondering if it's some kind of scrambled transmission or perhaps something not broadcasting correctly?
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snn47
Posts: 128
Joined: Tue Dec 27, 2016 11:00 pm

Re: Mystery 'drifting' signal

Post by snn47 » Mon Jan 21, 2019 4:06 pm

At the part of the ATC-COM band only AM DSB (25 kHz or 8.33 kHz spacin) is used so it is very unlikely usebs by civil or military ATC. While Europe is aiming to shift also for the lower airspace to a 8.33 kHz wide channel spacing the rest of the world is using 25 kHz channel spacing,

Did you check if it is a harmonic of a signal on a lower frequency e.g. f/2, f/3 and so on, of the frequency you tuned to?
More diffuicult to identify are spurious emission of a transmitter since they don't have to have a fixed relation like harmonics. e.g. from a wide band modulation or non linear products of a transmitter, CATV leackage powerline or some equipment in or around your home.
Use a directional antenna and try to identify the direction of the source, but my tip would be some spurious emissions in your home.
Let us know what you find

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