Re: [Discuss-gnuradio] PSK demodulator and Doppler

[Colby Boyer]

On Tue, Sep 2, 2014 at 10:09 AM, Mike Willis <address@hidden> wrote:

I am trying to develop a satellite ground station using the PSK demodulator block. This works fine when tuned accurately. However, with low satellites there is quite a bit of Doppler at VHF / UHF and there is also some frequency drift with satellite temperature as it enters or comes out of eclipse. This is a problem as the signals are relatively narrow in bandwidth compared to the Doppler and drift. I am wondering how to track this Doppler in Gnuradio. I have tried a PLL block and while this works it isn’t quite right unless the signal is very strong. It can also get fooled by one of the many spurious signals encountered on the bands.

 

To some extent the Doppler can be predicted and compensated for, but only when the orbital parameters are known accurately. Even a few seconds error at TCA can make quite a difference.

 

Has anyone solved this one?

 

Mike

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Is there a preamble/training sequence you can search for? If so, you can use that to get the initial frequency offset estimate to correct and then use the PLL to track the fine phase correction.