Inmarsat B/M/mM/Fleet monitoring?

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kb1ipd

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Hello.

In the past I've listened to inmarsat A, but as it seems, that service is on it's way out. Not surprising, considering the bandwidth and power needed for analog.

I was wondering if there was any software which could decode inmarsat digital voice. I know that HOKA can decode the tdma info as well as inmarsat C messages, but the voice channels would probably be beyond the capabilities of your standard sound card or modem.

I have recently become interested in the SDR-14 and other similar products, which contain a very high speed ADC and can function as their own demodulators, as software-defined radios. The bandwidth of these devices is very high and they are capable of some interesting analysis.

Could such a device, if paired with the proper software be used to decode such signals? Of course...I suppose I'd have to find out if the digital voice is encrypted to begin with...

~Steve
 

mancow

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Yea, A seems pretty much dead. I got into the hobby about 10-15 years too late it seems.


As long as you could pull out the O-CQPSK modulated data and run it through an AMBE vocoder there may be a possibility.

Some real deal units use Analog Devices brand DSP chips and an RF Micro Devices RF2711 Quadrature Demodulator which has now been replaced with the RF2713.

But, who knows if there is any other funny business going on such as encryption etc...


From the spec sheet...

The RF2713 is a monolithic integrated quadrature modulator/
demodulator. The demodulator is used to recover
the I and Q baseband signals from the amplified and filtered
IF. Likewise, the inputs and outputs can be reconfigured
to modulate I/Q signals onto an RF carrier. The
RF2713 is intended for IF systems where the IF frequency
ranges from 100kHz to 250MHz, and the LO frequency
is two times the IF. The IC contains all of the
required components to implement the modulation/
demodulation function and contains a digital divider type
90° phase shifter, two double balanced mixers, and baseband
amplifiers designed to interface with Analog to Digital
Converters. The unit operates from a single 3V to 6V
power supply.
 
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Johnnhattq

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Hi,
I need to receive Inmarsat-C by HOKA software(TDM,TDMA). Can anyone help me about the diagrams can receive Inmarsat-C ( I have as follows: anten L-band, Imarsat-feed, LNB, the code300-32 version 3.02, SDR-14, receiver ICR8500 or AOR5000, PC/WinXP)
John
 

brandon

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dsd?

Just searching around and stumbled across this thread. It would be interesting to see if DSD could support Inmarsat digital voice (assuming it's not encrypted). I don't know much about it but could be something to look into. Perhaps someone with an ideal setup could obtain some raw audio samples for analysis by dsdauthor? *hint* *hint* :)
 
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Inmarsat stuff

>Hi,
>I need to receive Inmarsat-C by HOKA software(TDM,TDMA).

The Hoka software is not particularly brilliant for Inmarsat-C reception. It will work, but the messages are poorly formatted, and of course it wont cope with any MIME attachments etc, or in fact 5 bit ITA messages, of which there are quite a few. You should forget the TDMA mode, it went off air as part of the Inmarsat-A deactivation some years back. The TDMA was simply for call allocation and a mux of low-rate 'telex' channels.

For reception, you simply need to get a reasonable signal from Inmarsat, it sounds like you have the right equipment for it. Once you can tune to the Inmarsat-C LES downlinks in SSB, you then need good software for the demod / decode. Have a look at the stuff available at inmarsatdecoder.com, and download the free demo.

>Could such a device, if paired with the proper software be used to decode such signals? Of course...I >suppose I'd have to find out if the digital voice is encrypted to begin with...

You'll find all the Inmarsat voice modes are 'encrypted' with with a 'scrambling vector' which is agreed between the LES and MES at the start of the call. Mini-M, M, and B use approximately the same system for scrambling. Inmarsat-GAN systems are using air interfaces based on a modified version of the GSM authentication system, so its probably difficult to break those. There is commercial software to decode M and B voice, as these use the IMBE codec for which there is a software decoder. Mini-M uses a modified version of the AMBE codec, presumably to further reduce errors caused by burst noise. There is not currently a solution for decoding Mini-M voice as far as I know. The M and Mini-M downlinks should be doable with a sound card and stable receiver, but as you say, a SDR on the input to the PC would be a lot better.

regards,

Paul
UHF Satcom (uhf_satcom) on Twitter
 

brandon

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Hmm looks like Wavecom has a product called W-Code-SAT
WAVECOM, the reference in data decoding

The SAT Option consists of:

* EasySATSystem
* INMARSAT B decoder
* INMARSAT C decoder
* INMARSAT M decoder
* INMARSAT mM decoder
* INMARSAT AERO-P decoder

Anyone lucky enough to use this program?
 

kb1ipd

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Anyone lucky enough to use this program?
It's actually not a program, but rather it's a hardware and software system. The hardware is either an external unit or an internal PCI card that has various inputs for IF off of receivers.

It's very very nice. Also, it's a bit rich for my blood (or rather, for my bank account). Last I checked it was over ten grand. The satellite monitoring feature is a software option and I'm not sure what their policy is on selling it. It might be restricted to certain authorized purchasers.

It looks pretty awesome, though. It decodes a lot more than Inmarsat.

By the way, if anyone is feeling generous, my birthday is on July 12. Feel free to buy me one ;-) I'll be your friend for life.
 
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