Re: [Discuss-gnuradio] Early Late Prompt Correlation and Costas Loop implementation

[Mir M. Ali]

I am using Flex-2400 boards and the received signal is ideally at baseband which in fact is not possible because, of various factors. Now, we have a signal that has a center frequency 'fc' which is not 0Hz. Assuming the costas to lock at this carrier I can achieve my goal. Isn't it right? 

Can you also tell me how fmax and fmin are calculated? For example, dbpsk.py has fmax=0.1 and fmin=-0.1. How do we get these?

Thanks,
Ali

On Wed, May 27, 2009 at 8:24 AM, Tom Lutz <address@hidden> wrote:

>
> As in Gnuradio there is no such thing as a carrier as the signal is in
> baseband what will the output of costas loop be so as to use it to get the
> Spreading sequence.
> I am sorry my concepts are not very strong but I am learning and such
> unresolved questions make this learning all the more difficult. Can you
> please tell me where I am wrong and what could be done.

The costas loop block (the one found in GRC and in the source code,
assuming you are using that one) actually outputs the incoming signal
multiplied by the synchronized carrier (assuming it has locked).  If
you tune the USRP off of the carrier you are interested in, that would
probably work, but that's from my naive view of the world.  For
example, if your carrier was at 465MHz and you tuned to 464MHz, you
might be able to bandpass filter and send to the costas loop the 1MHz
carrier.  The costas loop would output the downmixed signal downmixed
further, such that baseband is now 465MHz.

The min/max frequencies for the costas loop are in radians/sample, FYI.

Tom