HF Data Squitters Req Help ID'ing

[chgomonitor]

Requesting help identifying these HF data squitters I've been catching all up and down the bands. Attaching a somewhat poor quality .wav file I captured tonight.

Did an informal freq survey for these things across the 5 MHz band tonight and came up with;

5260
5290
5320
5350
5370
5380
5405
5430
5435
5750

These things seem to come and go at random between at least 5 and 10 Megs. Very distinct and rather wide squiggly RF waveform with lots of little audio peaks inside each squitter. Looks like some type of MFSK data burst. Looks like some variations in signal strength between the signals from here in the Midwest. They seem to come and go in some odd series, but almost random. Never very active on any single given freq. Might catch 2 or 3 in 4 or 5 minutes, then silent for 10 or 20 minutes. But as a network it seems to be always on. A couple of times I thought I observed some exchange type patterns, like groups were talking back and forth - but I could be wrong about that.

I'd love to take a crack at actually reading the little things, but for now I'd more than happy to learn what this network is. Anyone? Thanks in advance and...

Happy Scanning! - Ted

 

[DaveNF2G]

Get PC-HFDL.

 

[ka3jjz]

Compare the freqs to HFDL's Table 49, which we have here as a PDF, and is the most current we have today...

http://www.udxf.nl/HFDL-ACARS-VDL2-ModeS.pdf

and you will find the freqs he's reporting doesn't match up...

Ted you might post these on the UDXF Yahoo group and see if anyone has seen these. The logs are in the files area, and you can do an online search, too...a quick check shows 5260 having been used about 2 years ago by a group using RFSM8000, but that isn't necessarily what you have here.

Mike

 

[Token]

Your attached sound file is of an HF OTHR (Over The Horizon Radar) or a sounder, it is impossible to tell which from the recording. If you have a waterfall display a screen shot could help.

However, if you are seeing them several times a minute that is almost certainly an OTHR.

The waveform you have recorded appears to be a burst of LFMCW, typical of several different kinds of radars and sounders. I say appears because the recorded bandwidth is too narrow to confirm LFMCW, it might also be LFMOP. However, the users of LFMOP are few and far between, so odds are it is LFMCW.

One very possible source would be the Australian JORN, but there are other possibles.

The rep rate appears to be ~25 Hz. Assuming no coding beyond what is seen in the recorded file that would yield a maximum unambiguous range of about 6000 km for the system seen.

T!

 

[chgomonitor]

Update

Thanks for the very interesting input. I've worked HF ACARS/HFDL and this isn't it, although the thought had struck me that perhaps it's some new version - but I don't think it is.

I was chatting with some local friends who suspect it's some local QRM noise source. We have no shortage of every type of noise imaginable here in greater Chicagoland. It could be that or some internal noise from the computer / airspy sdr / NooElec upconverter box. But I've been DX'ing HF data and utilities for 40 years and I'm doubtful that this stuff is local interference - though I can't rule it out, either.

But the Over The Horizon Radar idea is really, really fascinating. For some strange reason I get fairly good reception from Australia and that area. North-South 60 foot random longwire at about 20 feet above ground with a coax shielded lead-in.I strongly suspect the signal is being generated by an automated sequence and the way these hop around all over the bands is highly suggestive (to me anyway) of some anti-jam countermeasures planning.

It's not going to be so much a case of a frequency list as these things hop around all over the bands at 20, 25 and 30 KHz intervals, and in a seemingly random pattern. Looks like true hopping to me.

These things are a bit wider than I thought. Via an IQ recording I recorded a squitter tonight centered on 6938 KHz. But when zoomed in and carefully measured it actually spanned 6933 to 6941, 8 Khz wide signal, wow. The USB filter in HDSDR is only about 1.8 Khz wide, so I've been actually only demodulating a little chunk of it as it sweeps around. I might try some audio captures in other, wider modes.

These things are hard to catch on a conventional receiver but in SDR displays they have a waveform that sticks out like a sore thumb, hard to miss. And watching the RF pattern come sweeping in while zoomed in on playback is pretty breathtaking. Then we come to the audio structure. I got a good capture on that tonight, too. What I thought was a 16 tone pattern is, well...I'll let the audio graph speak for itself. I, um, under-estimated this one. Again, wow.

Modern OTHR, eh? Could be...could very well be...fascinating. This thing must be screwing up HF 24/7.

I'll try insert the screen grabs of the RF fingerprint zoomed in and the audio graph here. I got a much better wav file capture on this particular squitter so I'll try to follow up with one zipped up for y'all. Thanks for the help...and...Happy Scanning! - Ted

Oh, and 131 Mhz = 6 Mhz thanks to the NooElec upconverter...

 

[chgomonitor]

Follow Up - Better Audio Recording

Zipp'ed .WAV file attached. - Ted

 

[chgomonitor]

One other note. A couple of weeks ago I really had these things coming in like gang busters and they weren't hopping quite so much. I was getting repeated squitters on a single freq in the 6 MHz band. Then, only once, exactly between two bursts I caught three quick little "dot" like beeps. Haven't heard that again. Transmitter tech at work??? - Ted

 

[Token]

But the Over The Horizon Radar idea is really, really fascinating. For some strange reason I get fairly good reception from Australia and that area. North-South 60 foot random longwire at about 20 feet above ground with a coax shielded lead-in.I strongly suspect the signal is being generated by an automated sequence and the way these hop around all over the bands is highly suggestive (to me anyway) of some anti-jam countermeasures planning.

It's not going to be so much a case of a frequency list as these things hop around all over the bands at 20, 25 and 30 KHz intervals, and in a seemingly random pattern. Looks like true hopping to me.

These things are a bit wider than I thought. Via an IQ recording I recorded a squitter tonight centered on 6938 KHz. But when zoomed in and carefully measured it actually spanned 6933 to 6941, 8 Khz wide signal, wow. The USB filter in HDSDR is only about 1.8 Khz wide, so I've been actually only demodulating a little chunk of it as it sweeps around. I might try some audio captures in other, wider modes.

These things are hard to catch on a conventional receiver but in SDR displays they have a waveform that sticks out like a sore thumb, hard to miss. And watching the RF pattern come sweeping in while zoomed in on playback is pretty breathtaking. Then we come to the audio structure. I got a good capture on that tonight, too. What I thought was a 16 tone pattern is, well...I'll let the audio graph speak for itself. I, um, under-estimated this one. Again, wow.

The frequency hopping seen by most OTHRs today is not really an anti-jam technique, although for sure in jamming environment it would have value. Note that you are seeing this action in a benign environment.

OTHRs must change frequency to illuminate the desired portion of the Earths surface and sky. While they often have good azimuth angle control they often have no or very limited control of elevation angle. Geometry involving elevation (and the layer of the ionosphere they are reflecting off of) is how they control where, down range, the energy "lands". With no elevation control the selection of frequency causes the signal to reflect from the ionosphere at different altitudes, the same affect as controlling the elevation angle.

There are also more complex issues of rep rate, frequency, and Doppler shift, and associated blind speeds, that are resolved with shifting frequencies.

On the interference front, a radar that hops causes less interference to other users of the spectrum, and also reduces any interference those other users would impart on the radar.

The width of these signals varies with type and current target set. From about 3 kHz to over 400 kHz widths are commonly used.

With HDSDR you should be able to adjust the USB filter width. The most usable data will result from a recording that is slightly wider than the swept width of the signal. This allows you to confirm sweep direction and whether it is FMCW or FMOP.

Modern OTHR, eh? Could be...could very well be...fascinating. This thing must be screwing up HF 24/7.

Not could be OTHR, this is OTHR, or an associated sounder. It can be difficult to discern the two, as they can use the same waveform, in fact some are called mini backscatter radars" in their own right. As a general rule if you see it active every few minutes or longer it is a sounder, more frequent would be a radar.

Actually modern FMCW OTHRs are less intrusive than something like the old Russian Woodpecker would be.

But there is no doubt, this is radar, or sounder, or both combined.

One other note. A couple of weeks ago I really had these things coming in like gang busters and they weren't hopping quite so much. I was getting repeated squitters on a single freq in the 6 MHz band. Then, only once, exactly between two bursts I caught three quick little "dot" like beeps. Haven't heard that again. Transmitter tech at work??? -

The three CW tones occur just before a burst, this burst can be alone or in a series of burst, with or without tones. No, it is not a transmitter tech at work, but rather is part of the signal. Exactly why these are sent has been the source of some questions, however I believe it might be used to detect very low Doppler shift targets that would be more difficult to detect with the FMCW.

T!

 

[a417]

Token...has spoken.


nicely done, bro.