Hi, I think this behaviour may be due to the level into the Polyphase Clock Sync block. The block expects a signal amplitude of 1 as explained in [1].
An AGC between the Correlate and Sync and the Polyphase Clock Sync blocks might do the trick. Cheers Ernest [1] https://destevez.net/2017/08/agc-for-gr-satellites/ On Wed, Jul 10, 2019 at 6:22 AM Achilleas Anastasopoulos <anas...@umich.edu> wrote: > Hi all, > > I am not very successful in running the uhd_corr_and_sync_tx/rx.grc > example in the gr-digital examples directory (3.7.13.5) using usrps. > > In an effort to debug it, i merged the two graphs and eliminated the uhd > sink/sources (see attached) and so I am running a simulation without the > usrps. I also eliminated the FLL block as I do not have any frequency error > and not even any noise. > > The behavior I see is as follows: > > The transmission seems fine (a nice rrc spectrum followed by silence > periodically on and off). > On the reception side the blocks seem to be working fine producing > appropriate tags (one every 20Ksamples as expected) which means that the > "correlate_and_sync" block works as expected. > > When I plot the output of the "polyphase_clock_sync" I expect to see three > clear points: +/- A and 0. Indeed this is what I see at first. > > Now I do the following: I increase the noise for a while to a large number > (~10dB) and then I take it back almost to 0 (-20dB). From that point on, > although the "correlate_and_sync" block works as expected (I see the tag > offsets back to normal) the picture does not contain three clear points but > is blurred indicating that the "polyphase_clock_sync" does not work > appropriately and I can never recover from this. > > I was hopping that since the "correlate_and_sync" block recovers and adds > the appropriate tags to the stream, the downstream block can recover as > well. However the behavior is not as robust as I expected. > > Can someone shed some light into this. > > thanks > Achilleas > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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