Russian navigation satellites

[AlanC]

Hi All,

Daft as it sounds, this IS vintage technology; the Russian Parus navigation satellite system has been around since the early 1970's and, I suspect, won't be with us for that much longer. I'm in the process of recording passes and preparing an in-depth article for my website about them, so that when gone it is at least recorded for posterity.

I'm writing a software program in Java that decodes the data transmitted from the satellites. The program uses a WAV file recording of a satellite pass as its input source, and it synchronises to the 50 symbols/sec fsk transmission from the satellite which uses tones of 3, 5 and 7 kHz. The program uses some novel techniques to improve the SNR of the signal. So far, I am able to recover the symbols from each one-second 50-symbol frame, convert them into binary data, and I can decode the time (Moscow time, UTC + 3) easily from the first 18 bits. Although not intended as a real-time decoder, early indications are that it is way more than fast enough- it processes a wav file some 20-50 times faster than the wav file would play; I'll post some screenshots later.

As stated above, in each frame, the first 18 bits are the time in hours minutes and seconds, the remaining 32 bits being an information word. What I really need is any information at all on the content of the individual words within these blocks, and how they can be used to calculate the coordinates of the spacecraft and others in the constellation.

I have a copy of Wood and Perry's classic paper from 1978 'The Russian Satellite Navigation System' describing the basics of the signal format, breaking down the 60 frames transmitted in a minute into a number of information blocks each of 7 words.

I've been interested in this satellite system for years, and I remember that there was an article in PW or PE in the 80's or 90's that described it in a lot more detail than Wood and Perry, and I would dearly like a copy of that magazine article if anyone can lay their hands on it. Or, can someone please tell me who the author was?

Currently, Cosmos 2407, 2414, 2429, 2454 and 2463 are the operational satellites (the latter only being launched in April last year) and are all working fine. It's civilian opposite number, the Tsikada system, was shut down in 2009.

Any assistance would be most gratefully received.

Many Thanks,
Alan

[AlanC]

Screenshot of decoder app as promised

[davegsm82]

I'm quite interested in stuff like this, and i've been told you can pick up the transmissions on a normal scanner, is this correct? If so, what frequency?

I imagine the data words are going to contain similar information to the current US System that we all use for our sat-nav's. Things like, Sat ID, altitude, speed, direction perhaps.

Dave.

[neon indicator]

Certainly I pick up the NOAA satellites at 137MHz on a Discone. A cheap scanner is better than the comms receiver as the wider IF makes it less affected by doppler shift.

Frequency is 149MHz approx, so a discone + cheap scanner may well work.

I use orbitron to track orbits.

[AlanC]

Satellite fVHF launched Norad ID
cosmos 2407 149.970 22/07/2004 28380
cosmos 2414 149.970 20/01/2005 28521
cosmos 2429 150.030 11/09/2007 32052
cosmos 2454 149.940 21/07/2009 35635
cosmos 2463 149.940 27/04/2010 36519

These satellites are very easy to receive on a handheld scanner though obviously you'll get better results on an external antenna. The tx power is about 10 watts (+40 dBm) so with a 140dB path loss on an overhead pass (alt = 1000 km) you'll get about a microvolt in a zero-gain antenna, which is enough to hear. As Neon indicator says you'll need a predictor program- there's loads out there for free, I use GPredict on Linux; you can even get one for an android phone! Try to pick a near overhead pass for your first attempt; and don't forget to set the program to UTC not local time!

The VHF frequency carries the time data and orbital parameters for the current and other satellites. There is a second transmission on around 400MHz- its in an 3:8 ratio with the VHF carrier frequency. This is unmodulated- i.e cw. It is used to measure the Doppler shift, to determine when the satellite is dead abeam the observer. The transmitted time, and the orbital data, tell you where the satellite was in the sky when that happened- or, put another way, if you know where the satellite is relative to you, then you know where you are- well, you're somewhere on a line at right angles to the satellite's track. You then wait for another satellite, and obtain another poition line- and where they cross, then bingo- that's where you are. Hope that makes sense!

Parus could give you a fix in 1-2 hours; and had an accuracy of 100m anywhere on the earth's surface. Okay that's poor compared to GPS, but in the 1970's it was revolutionary.

It isn't just Doppler that determines the receiver bandwidth, although you do take it into account. Most satellites have a much higher FM deviation than a normal narrowband FM transmission- the NOAA met sats are about 19kHz deviation I think- and these nav sats are higher too, but not that much. But for decoding, you do need to resolve the 7kHz second markers which a narrow filter won't easily do. I'm using a Yupiteru MVT7200 to do my recordings with and it works very well.

Best regards,
Alan

[m0cemdave]

I remember that there was an article in PW or PE in the 80's or 90's that described it in a lot more detail than Wood and Perry, and I would dearly like a copy of that magazine article if anyone can lay their hands on it. Or, can someone please tell me who the author was?

Radio & Electronics World ran a series of articles on this. I only have Part 2, appearing over 6 pages in the February 1985 issue. I presume Part 1 was the previous month, and there's a reference to more "next month" so it must run through at least 3 issues.

Authors were P Daly and M Leybourne, (Dept of E&E Engineering, University of Leeds) and PA Pitts of the University of Leeds TV Service.

HTH

[AlanC]

Dave, that's fantastic and might well be the one- does that part that you have contain any info on the message format?
Alan

[KeithsTV]

I have all 3 issues with the articles which I can scan if required.

Part 1 does have some details of the data format.

Part 2 has details of the hardware used to receive the signals.

Part 3 has details of software.

Keith

[m0cemdave]

Originally Posted by KeithsTV

I have all 3 issues with the articles which I can scan if required.

Part 1 does have some details of the data format.

Part 2 has details of the hardware used to receive the signals.

Part 3 has details of software.

Keith

Don't scan Part 2....

I have today scanned it, cleaned it up, and uploaded as follows:

www.spamabyss.net/pictures/RuSats2p1.jpg
www.spamabyss.net/pictures/RuSats2p2.jpg
www.spamabyss.net/pictures/RuSats2p3.jpg
www.spamabyss.net/pictures/RuSats2p4.jpg
www.spamabyss.net/pictures/RuSats2p5.jpg

Files are quite large, between 400 and 1200k each, but they should print to A4 at 360dpi.

Hoping this is helpful.

Dave.

[AlanC]

Dave,

That's fantastic, thank you very much for doing this, I am most grateful.

Keith,

I would really appreciate it if you could scan the other two parts for me... thanks in advance.

Best regards
Alan

[KeithsTV]

Here's parts 1 & 3 of the series.

Keith

[AlanC]

Thanks Keith, that's absolutely spot on- got all the info I need. I can crack on with the coding now!

Thanks again
Alan

[AlanC]

Okay, well thanks to that info and a bit of deduction we now have an application that decodes all of the data. In the picture below you can see that the satellite being received (it was Cosmos 2407) is sending blocks of Keplerian orbital data- the ephemeris- for the various satellites in the system.

When the web article is finished, the application will be available to download and use free for both Windows and Linux from my website.

Thanks all; yet again, the members of this forum have come up with the goods!

Best regards
Alan

[neon indicator]

Brilliant Alan. Since I have successfully received WX images via the 137MHz sats, I fancy a go at this.

[julie_m]

Hmm ..... I wonder if those little Russian valves could be used to make a receiver for the Russian satellites?

Might they even be what's in the satellites?

[neon indicator]

149MHz is pushing it.

There is a VHF-FM radio though.

[nerdsville]

Hi, new to the forum.

I stumbled across this thread while investigating an identified signal on my scanner which turned out to be this Russian navigation system.

I have got back into the hobby after a break of many years and been passing the time decoding all the strange data signals you now find on the VHF/UHF bands so I was intrigued by Alan's decoder and wondered how it was progressing?

[davegsm82]

Welcome to the forum nerdsville,

sounds like you're doing some interesting research, are you listing your findings anywhere?

Dave.

[nerdsville]

Hi Dave,

At the moment just using various decoders available on the internet for paging, taxi-mdt, trunking etc. But there are lots of other mysterious telemetry, data and digital transmissions out there.

In the past I've decoded NOAA APT weather satellites, and more recently been getting the odd SSTV images from the ARISSat-1 amateur radio satellite.

I do update my blog with updates.

[scottph59]

I am getting into decoding the navsat birds and wondered if the java decode program is available anywhere? Thanks. Scott