Strange Slow Sweeping Signal

[AlaskaMike]

I found a strange one that appears to be an extremely slow descending sweep from at least 4255 kHz through 4244 kHz (where I found it, and where it's descending through as I type this). I would've thought this was some kind of noise, but I've never seen or heard of any noise that slowly shifts frequency like this, especially in such a slow and consistent manner.

I took the audio and screenshot below at about 0940z. Anyone have any ideas what this might be?

http://www.tibor.org/slow-sweep.wav
http://www.tibor.org/slow-sweep.jpg

It really looks more like noise to me, but that slow frequency change seems uncharacteristic.

 

[n2nov]

See this thread:

http://forums.radioreference.com/utility-listening/230454-4200-4250khz-strange-pulsing-signal.html

 

[AlaskaMike]

Sorry, but what I posted is nothing like the CODAR referred to in that thread. I hear CODAR all the time, and it sounds exactly like the .wav file example titled "What does a Long Range 5MHz SeaSonde sound like?" given in the post by Bryan Herbert in the thread you referenced.

What I posted sounds nothing remotely like that.

 

[Token]

Congratulations, you have found a ... ... ... wait for it ... ... ... slow sweeper.

Well, that is what I call them in my log anyway. As far as I know no one has actually identified what these are for sure. Several times folks have attempted to tie these signals to a system such as a sonde of some kind, and that is the most likely answer if they are intentional.

In my opinion, and I freely admit this is opinion, not something I can prove, most of these are unintentional radiation. Most that I have looked at do not repeat in a controlled manor, ie, when they come back the next time they are not really the same frequency extent (start/stop freqs or swept width), or they appear at irregular intervals. Most sonde type signals have a pattern that can be detected. However, arguing against unintentional, they almost all seem to sweep down in frequency, and that does not quite seem random enough.

However, I have seen a few similar signals that are very regimented, as in show up the same time every day and sweep the same freq range every day or specific time period. Those would probably be intentional. So it is quite possible there are many sources that make similar signals, and they all kind of get lumped together by listeners.

Upshot of all of that? I don't know what they are, and I have never talked with anyone who does know for sure what they are what they are, but I have talked with a lot of people who have heard them. I personally have heard them, or similar signals, since the 70's for sure and maybe even the 60's.

T!

 

[AlaskaMike]

Interesting. While I was tuning around after I posted last night I found two more, one of them in the 80m band around 3560 if I recall. I didn't write down any details, however that one was definitely sweeping upward in frequency at the time I first caught it. When I searched for it a couple minutes later it was stationary (the waterfall lines were vertical), and a few minutes after that it had started back down the band.

All three that I found last night seemed identical in signal strength and there was no fading at all, which was part of the reason I thought it might be noise.

 

[AlaskaMike]

In progress again on 3578, and sweeping up in frequency. I notice blips in the waterfall where the lines will shift up about 10 Hz briefly, and I'm wondering if that's modulation.

 

[AlaskaMike]

Here's an interesting data point--I was tuning around the 80 - 75m bands over the past 30 minutes because they seem to be wide open as I type this, but I was amazed to copy 75/850 RTTY on about 3550 kHz. I was just getting reconfigured for it when it stopped, and then the slow sweeper started immediately. This was at approximately 0809z. There was about a quarter second gap that was very distinct. To me the transmitters appear to be the same strength.

The signal is climbing up through 3585 as I type this, slowing it's ascent--the waterfall lines are almost vertical..