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[Discuss-gnuradio] pfb clock sync

From: Nick Foster
Subject: [Discuss-gnuradio] pfb clock sync
Date: Mon, 13 Feb 2012 18:39:53 -0800

Hi all, 

I've been doing some stuff with the pfb clock sync for GMSK (my AIS app again) and had a couple questions. First, a sanity check so you can tell me if I'm just nuts:

BT = 0.35
self.filtersections = 32
self.tapspersection = 20
self.clockrec_sps = 1
gain_mu = 0.03
self._samples_per_symbol = 250.0e3 / 9600.0
self.datafiltertaps = gr.firdes.gaussian(1, self._samples_per_symbol*self.filtersections, BT, self.tapspersection*self.filtersections)
self.clockrec = gr.pfb_clock_sync_ccf(self._samples_per_symbol, gain_mu, self.datafiltertaps, self.filtersections, 0, 1.15, self.clockrec_sps)

Am I constructing the filter correctly? If not, don't bother reading further, just tell me I'm a rube and move on. =)

If not, increasing the output samples per symbol (self.clockrec_sps above) to 2 seems to cause the clock recovery to go off into the weeds. Any reason for this? Does the filter construction need to change when using multiple osps?


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