Unidentified floating signal, in 2m band

[lw3haz]

The info below is full of estimated guesses... I'm no expert!

I was monitoring a failing ham satellite (I suspect) TO-108). It seems to transmit only when receiving sunlight. As it seems to be tumbling or rotating, the ystem seems to restart each time. It does transmit BJ1SV in morse code, so that confirms its origin...

Now, while doing that, I heard short bursts of another signal. Only after widening the waterfall range (a lot) did I notice that the signal is actually drifting - quite rapidly - in a downward direction, over a range of over 1MHz. Here are some characteristics:
- The scan range and speed varies randomly
- I can't find any modulation, though there seem to be frequency jumps
- I've been looking at the sig for more than an hours, which would exclude the possibility of a LEO satellite (which would mostly limit the visibility to about 14-15 minutes, though the repetitivity could also indicate 'tumbling' and sun dependency.
- It start at the upper frequency then floats to the lower
- then disappears for tens of seconds
- and restarts.
- the scan range is large - 100's of kHz (not comparable to the TO-108.
- The signal level change quite drastically.

This is an example of such a signal. (Note that the waterfall 'falls': The top is the most recent:

 

[merlin]

What satellite is this ?

 

[lw3haz]

What satellite is this ?

That's exactly my problem - I also doubt it is a satellite...

 

[merlin]

The steady signal does look like a beacon, can you decode it ?
I ferreted through all the amateur sat frequencies an dont find this.
Been watching SDR# and nothing there in NW US.

 

[lw3haz]

Hi Merlin. Thanks for your investigations. The vertical - steady - lines are probably caused by some strange intermodulation of nearby FM transmitters. A recurring themes is a carrier at a multiples of 100 kHz, and two sidebands 19 kHz, probably the FM's pilot tone... These dongle SDRs are very sensitive to large signals, though in this case I suspect the IM is caused between the FMs themselves. But that's another subject.

 

[merlin]

Yea, that is a problem with these cheaper SDR dongles. I needed to update my tracking software TLEs anyway.
Do you suppose it could be an image of over the horizon radar ? I have seen a bit of that.
Also, a nearby scanner searching frequencies could leak enough VCO to be picked up on a nearby receiver.

 

[lw3haz]

Over the horizon Radar? Never hear of that on VHF, I doubt that's the QRM.

Anyway the QRM continues, erratically. It scans about 500+ kHz between 144 and 146 MHz. Apparently no relation with temperature etc.

Years ago we had a similar problem with a very old (analog) TV antenna amplifier. I seriously doubt there are still of those active.

 

[KK4JUG]

Be sure to check some of the least likely places, too.

Several years ago while I was still a LEO, the department got a call from the airport control tower. They had an aircraft beacon going off. They weren't missing any aircraft and a crash is hard to miss in an urban area so it wasn't an emergency. Still, it needed to be quieted. I got the EMA director (and his Icom aircraft portable radio) and we went to work. It was narrowed down to a older well-established middle class neighborhood. Using the radio with a bread wire tie as an antenna (that's a whole different story), we pinned it down to a vocational high school. As it turns out, someone had donated an old aircraft fuselage (I think it was a Piper Sundowner) to the school and one of the students apparently activated the still-viable beacon.

Ya never know.

 

[merlin]

Over the horizon Radar? Never hear of that on VHF, I doubt that's the QRM.

Anyway the QRM continues, erratically. It scans about 500+ kHz between 144 and 146 MHz. Apparently no relation with temperature etc.

Years ago we had a similar problem with a very old (analog) TV antenna amplifier. I seriously doubt there are still of those active.

If you get mixing, it can happen, but usually related to strong OTH signals, I never looked at AWACS radar, if something they use slides like that,you could get mixing up to UHF frequencies.