Re: [Discuss-gnuradio] Bug in gr_quadrature_demod_cf, or scheduler?

[Matt Ettus]

Steven Clark wrote:
> Hi all-
> please look at this sequence of eye diagrams:
> http://picasaweb.google.com/steven.p.clark/GMSKFmdemodGlitches
>
> These are from a gmsk mod/demod pair, showing the output of the TX's
> gaussian filter (blue) overlaid with the output of the RX's fmdemod
> (red). BT = 0.35.
>
> At 8 samples per symbol, everything looks ok. Red is pretty much right
> on top of blue, as we'd expect.
> As I increase samples per symbol, however, something strange happens,
> shown in plot sequence. The RX's fmdemod output gets successively more
> "glitchy".

One other thing -- you really shouldn't be going to more than 8:1
oversampling on GMSK anyway -- all the timing recovery stuff will have
trouble with that high of an oversampling rate when you have noise on
the signal.  We still need to fix this problem, but I would advise
staying at 8:1 or lower.  Your bandpass filtering also becomes harder at
the higher oversampling ratios.

Matt