please look at this sequence of eye diagrams:
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
BT = 0.35.
At 8 samples per symbol, everything looks ok. Red is pretty much right
top of blue, as we’d expect.
As I increase samples per symbol, however, something strange happens,
in plot sequence. The RX’s fmdemod output gets successively more
If I (in python) do the same thing that gr_quadrature_demod_cf is doing
def fm_quadrature_demod(re, im, gain):
num_c = min(len(re),len(im))
out = 
for i in range(1,num_c):
the glitches do not exist. This tells me that TX fmmod output is fine.
Something is going wonky as gr_quadrature_demod_cf does its work. Any
Is this a problem with the scheduler?
Code attached (incidentally, I tried using the old style flowgraph,
hier_block2 / top_block, glitches were still present).