Mysterious "chugging" signal

[KE7IZL]

I don't know what this is but I've included a zip file http://www.mediafire.com/?yb1l7a260yci583 containing an MP3 audio recording and a PNG of the spectrogram. It is on 3.286MHz. Receiver mode is USB. I can only describe it as a "chugging" sound like a running truck engine or something. And it has lots of selective fading (which on the spectrogram look like someone went in with an eraser and took out various parts of it in different places), and makes a wooshing sound of changing pitch in the audio. I first heard the signal when I tuned to the above mentioned frequency. It was already going when I got there at 7:55 UTC, and it is still going now as I'm writing this message at 8:06 UTC.

What type of digital mode is it?

 

[KE7IZL]

Found another VERY similar signal just now on 4.275MHz USB, at 8:26 UTC. I believe it may be the same mode, however this one's spectrogram is a bit different, it's never the same over a period of time, whereas the spectrogram from the one in the opening post looks like it repeats every 1/10 of a second. I'm guessing the first one I found was idling, but this one here is transmitting data. I'd make a second post for it if I believed it was a different digital mode (I may regret this later) but I'm not bothering with that as I believe it's just data transmission using the digital mode I've already documented (it has that same "chugging" sound like a truck engine). This signal too is experiencing the ionospheric effect of selective fading (and VERY heavilly too).

This tells me the transmitter (neither with this signal, nor the one in the opening post) is not able to reach my location without ionospheric bounce, meaning both signals have a source quite some distance away from my location (possibly hundreds of miles away from Seattle, WA).

 

[Token]

While I do not consider myself an expert at digital modes, in fact I think of myself as rather a newb in the area, I believe the audio example you posted sounds rather like STANAG 4285.

One of the ways to help in ID of these types of modes is to catch the beginning or end of the data. Several modes can be quite similar but have pilot tones or other identifying features that can be heard at the start of a data transmission.

Also, a program you might find a bit more useful than Argo for these types of things is Spectrum Lab. Nothing wrong with Argo, but Spectrum Lab brings a few more tools to the job.

T!

 

[KE7IZL]

Nothing wrong with Argo, but Spectrum Lab brings a few more tools to the job.

T!

Spectrum Lab kills my CPU. It always makes my CPU run at 100% capacity. All other programs run slow as a turtle when Spectrum Lab is running. Often times, even when it's the ONLY program running it can't keep up with the processing algorithms it uses, and the sound "skips".

 

[Token]

Spectrum Lab kills my CPU. It always makes my CPU run at 100% capacity.

Is it rather an older PC? I run Spectrum Lab, when i bother to run it, on an old Pentium 4 HT with 1 GB RAM, XP Pro machine, that I put together in 2003 or so, and it seldom gets above the 25% point on the CPU. I can run Spectrum Lab, Perseus GUI and hardware, and SpectraVue with an RFSpace SDR all at the same time with no pauses, drops, or issues on that machine.

T!

 

[KE7IZL]

Is it rather an older PC? I run Spectrum Lab, when i bother to run it, on an old Pentium 4 HT with 1 GB RAM, XP Pro machine, that I put together in 2003 or so, and it seldom gets above the 25% point on the CPU. I can run Spectrum Lab, Perseus GUI and hardware, and SpectraVue with an RFSpace SDR all at the same time with no pauses, drops, or issues on that machine.

T!

I think my CPU speed is only 2GHz, and I believe it only has a single core processor.

 

[SCPD]

BTW, yes the signal is S4285.

 

[KE7IZL]

BTW, yes the signal is S4285.

Why couldn't I decode with MultiPSK in 4285 mode? I tried different frequency polarity (USB LSB) and tuned up and down to center the signal on MultiPSK's waterfall, and I couldn't decode anything. So that's for the heads up about the Stanag 4285. If you hadn't told me I'd have thought it was something else based on my MultiPSK experience with it. Is it maybe encrypted? Or maybe just too much fading?

 

[Token]

Why couldn't I decode with MultiPSK in 4285 mode?

<<snip>>

If you hadn't told me I'd have thought it was something else based on my MultiPSK experience with it. Is it maybe encrypted?

Yes, many, probably even most, S4285 transmissions are encrypted.

T!