Thanks Josh and Dave, I will start experimenting with Dave's suggestion for the Polyphase Clock Sync because I already built the GRC flow graph, just that I could not get it to work.
Then, I will move onto experimenting with the other suggestions. Regards, George On Wed, Mar 10, 2021 at 9:39 AM J M <mor...@gmail.com> wrote: > There is also an excellent presentation on Timing Recovery from GRCON 17 > by Andy Walls: > https://www.youtube.com/watch?v=uMEfx_l5Oxk > > The clock sync block described in this presentation (which lives in-tree) > is intended to supplant the polyphase clock sync block since it covers more > timing recovery options. > > Josh > > On Tue, Mar 9, 2021 at 5:10 PM Dave Miller <dave.todd.mil...@gmail.com> > wrote: > >> George, >> >> I would recommend that you start with the below referenced example symbol >> sync flowgraphs and parameter settings and tutorials first, get them up and >> running well, and then tweak the symbol sync block settings to your desired >> parameters/settings for your scenario: >> >> - .grc examples: You can find some symbol sync example flowgraphs >> with gnuradio version 3.8.2 installed on >> usr/share/gnuradio/examples/digital/demod >> - GRCon 2019 Slide Presentation: I developed the tutorial >> presentation at the following link in order to help get others up and >> running quickly with the Polyphase Clock Sync block including the RRC >> filter taps. See slides #8 and #10 for the exact parameter settings that >> may answer your question. It was done in gnu radio version 3.7.11, but the >> flowgraph and all its parameter settings still work in version 3.8.2. >> >> >> https://www.gnuradio.org/grcon/grcon19/presentations/NASA_Space_Communications_Network_Modem/ >> >> - GRCon 2020 Presentation Video: Daniel Estevez’s video tutorial uses >> the other symbol sync block in gnu radio with the Gardner TED selection. >> You can pause his video at about 1:01:24 with the symbol sync “properties” >> box open and see all the exact settings. >> >> https://www.youtube.com/watch?v=RDbs6l4rMhs >> >> You may also want to check your symbol rate frequency offset setting >> between your modulator and the symbol sync block and verify that the >> frequency offset is not too large for the loop bandwidth of the symbol sync. >> >> Hope the above is useful, >> >> Dave >> >> _________________________________________________________________________ >> >> *From*: George Edwards >> *Subject*: Questions on Polyphase Clock Sync block >> *Date*: Mon, 8 Mar 2021 16:21:22 -0600 >> ------------------------------ >> Hello, >> >> My goal is symbol timing using the Polyphase Clock Sync block. I >> generated a QPSK waveform which I input to the Channel Model block with >> epsilon set to 1.0005 (small signal timing offset) and pass the signal to >> the Polyphase Clock Sync. The Polyphase filter is designed to run with 32 >> arms and receive the tap coeff's from the RRC Filter Taps. The parameters >> for RRC Filter Taps block are are set with defined variables as follows: >> Gain =1 >> Sample_rate (Hz): sample_rate >> Symbol_rate (Hz): sample_rate/sps (where sps is samples/symbol and >> defined) >> Excess_BW: excess_bw >> Num Taps: 32*(sps*6*2) (designing for overlap of +/-6 symbols >> with "sps" >> samples/symbol) >> 1) When I run the GRC and look at the constellation plot at the output of >> the Polyphase Clock Sync, all I see is a dot at the origin of the I/Q plot. >> >> 2) So I tried changing the number of taps to see if things change and >> only when I try the number of taps equal to 32*11 do I get something that >> makes some sense. I get data over the 4 quadrants between +/-.04 +/-0.4j, >> spread out. Of course, it keeps smearing into one. >> >> Will appreciate any suggestions on how to use the Polyphase Clock Sync >> block in conjunction with the RRC Filter Taps for symbol timing. >> >> Thank you! >> >> Regards, >> George >> >
