Re: [Discuss-gnuradio] XM on GR

[Chris Kuethe]

Thanks to Steve for hitting me with a clue-stick. For anyone else
playing along at home, the Sirius patch antenna has an integrated amp
and takes inline power - a fact that I did not see anywhere.

This test was done with a hackrf tuned to 2.3265GHz, 20Msps, 8MHz
analog filter - there is clearly something interesting going on when
inline power is enabled with the "bias=1" argument.

On Sat, Apr 9, 2016 at 6:32 AM, Andy Walls <address@hidden> wrote:
>
>
> On Fri, Apr 8, 2016 at 10:48 AM, Andy Walls <address@hidden>
> wrote:
>>
>>
>> >         The audio codec is proprietary and not documented anywhere AFAIK
>> > so
>> >         even if you demod the bitstream, you won't be able to do much
>> > with it.
>>
>> > Thank you all for the conversation, it is pretty interesting.  That
>> > makes sense
>> > that they have a proprietary protocol, it's a shame though.  Is the text
>> > that
>> > comes through encoded in a proprietary way?
>> >
>> > Does anyone know what the frequency of channel 1 is on (I'd like to see
>> > if I
>> > can even see the signal popping up above the noise)?
>> >
>> > ~Jason
>>
>> The XM center freqs are shown here:
>>
>>
>> https://www.rohde-schwarz.com/us/technologies/satellite-broadcast/xm-satellite/xm-satellite-technology/xm-satellite-technology_55613.html
>>
>> The Sats are QPSK, the terrestrial is COFDM.
>>
>> That page also states the audio codec for voice programming is AMBE, and
>> AAC+ for all other programming.
>>
>>
>> The XM radio patents give you a lot of clues:
>>
>> https://www.google.com/search?tbo=p&tbm=pts&hl=en&q=inassignee:%22Xm+Satellite+Radio+Inc.%22
>>
>> Images 4 and 6 of this one:
>>
>> https://www.google.com/patents/US7020217?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22&hl=en&sa=X&ved=0ahUKEwj5ycbeoP_LAhXEXh4KHWSdDeA4HhDoAQgwMAM
>> Image 4 of this one:
>>
>> https://www.google.com/patents/US6510317?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22&hl=en&sa=X&ved=0ahUKEwikn4Ogof_LAhVIJx4KHYaYCt44KBDoAQhTMAg
>>
>> And maybe the most useful I've skimmed:
>>
>> https://www.google.com/patents/US7123875?dq=inassignee:%22Xm+Satellite+Radio+Inc.%22+MCM&hl=en&sa=X&ved=0ahUKEwidqpT1of_LAhUFXh4KHXqIDuEQ6AEIKjAC
>> Images 1, 5, and 6.
>>
>> This particular patent also indicates that after the demod, RS decoder,
>> viterbi decoder, and deinterleaver, that an MPEG TS *might* be the
>> transport multiplex.
>>
>> The images show that the decryption happens after all the FEC and
>> deinterleaving is handled and also after SL (service layer) decoding.
>> The I2C connected external NVRAM is likely where the program decryption
>> key is stored (inside of a tamper boundary), according to other internet
>> pages from 7 years ago.
>>
>> So I'm guessing you have to totally demodulate and decode one of the SAT
>> or terrestrial channels, and then dig around in a (hopefully MPEG)
>> transport stream to find your unencrypted "Channel 1"
>>
>
> The STA400A datasheet gives a lot of good information about the XM signal
> characteristics, bit rate, RCC filter bandwidth, code rates and puncturing,
> proper order of FEC blocks, etc.:
>
> http://www.chipfind.net/datasheet/pdf/stmicroelectronics/sta400a.pdf
>
> Enough info to give one half a chance of getting the demodulation correct.
> It also talks a little bit about the frame structure.
>
> This MAXIM 2140 App Note has a yet another picture of the spectrum
> allocation, that also shows Sirius' and WCS' allocations in context:
>
> http://pdfserv.maximintegrated.com/en/an/AN3851.pdf
>
> I also found a Sirius patent that talks about an overlay modulation, but it
> wasn't clear to me if it was being applied to the XM satellite signals.
>
> Regards,
> Andy
>
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>



-- 
GDB has a 'break' feature; why doesn't it have 'fix' too?

hackrf_sirius_with_bias.png
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hackrf_sirius_no_bias.png
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