I think there is an overlay modulation. I'll try dig up the source where I
saw that.
On Apr 7, 2016 16:30, "Steve Katzberg" <[email protected]> wrote:

> Jason,
>
> I am involved in a project that needs the bit stream from XM but we do not
> need it decrypted.  The acquisition of the unencrypted Channel 1 would be
> fun to do, but so far I cannot get Gnuradio blocks to properly lock on to
> the signal.  The Costas loop drifts through he QPSK constellation, but
> won't stay locked on it.  That probably means I don't have something right
> in GRC or there is an overlay modulation that confuses the Costas loop
> phase locking.  Until either my hybrid hardware/GRC setup starts locking
> onto the XM signal there will be no Channel 1.
>
> Steve Katzberg
>
> ----- Original Message -----
> *From:* Jason Matusiak <[email protected]>
> *To:* GNURadio Mailing List <[email protected]>
> *Sent:* Thursday, April 07, 2016 5:14 PM
> *Subject:* [Discuss-gnuradio] XM on GR
>
> I was thinking about XM radio today and how channel 1 on it is sent in the
> clear (if you don't have a subscription, you can tune to it and hear their
> adds).  I haven't found a lot of information (so I think I know the
> answer), but has anyone looked into an XM receiver in GR?
>
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