My solution involved the frequency translating block and a third party application. As part of the initial channel filter, I set the the "Center Frequency" attribute to -40000+fftshift*rx_shift_factor (assuming my LO tuned to +40 KHz from the carrier). The satellite tracking program, PREDICT, provides a Doppler shift calculation assuming a 100 MHz carrier. rx_shift_factor is the satellite carrier frequency divided by 100 MHz. I then polled PREDICT, which provides a UDP server interface and then in Python called set_fftshift method on the flowgraph object generated by gnuradio-companion. In turn, this would update the taps of the FIR filter to provide a desired frequency shift.
As for temperature drift, I assumed that with a strong enough signal, the inbuilt Costas loop would be able to bring the signal back to baseband. The drawback of this solution is that it's not fully contained within gnuradio-companion, and like you said, requires the orbital elements to be known. One solution that uses the PLL block is here: https://www.cgran.org/wiki/ESTCube-1Receiver On Wed, Sep 3, 2014 at 4:53 PM, Mike Willis <willis...@gmail.com> wrote: > Hi Colin, > > > > Not really, though there is an AX25 style header. Far from ideal 01111110 > flags. > > > > Mike > > > > *From:* Colby Boyer [mailto:colby.bo...@gmail.com] > *Sent:* 03 September 2014 03:11 > *To:* Mike Willis > *Cc:* GNU Radio Discussion > *Subject:* Re: [Discuss-gnuradio] PSK demodulator and Doppler > > > > On Tue, Sep 2, 2014 at 10:09 AM, Mike Willis <willis...@gmail.com> 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 > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > 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. > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
