Using predict is a similar solution to what I do in simple_ra for "fringe stopping", except that it's all contained within the same chunk of
Python, using a "helper" function that's tied to a every-5-seconds polling loop. The helper function calculates the required phase rotation, given a number of input parameters relating to the observation. On 2014-09-03 09:03, Tom Rondeau wrote: > It might not be completely contained in GRC, but it's a clever solution. > > Another thing to look into is the fll_band_edge block. This will only work, > however, if the signal is pulse-shaped. Specifically with an RRC filter by > design, but we can modify it for other pulse shapes as well. This only does > coarse frequency correction, but it's lock in bandwidth is much wider than > that of the Costas loop block. You'd still want to follow this up with the > Costas loop for fine frequency and phase tracking. > > One thing, too, is that this block is fairly expensive computationally. It's > calculating two FIR filters, which should be replaced by fast convolution > filters. And I think that we could even combine this into a single filter > operation. > > Tom > > 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 [1] > > 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 [1] _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [1] _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [1] Links: ------ [1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
