[Discuss-gnuradio] Decimation Rates

[Andrew Buck]

I'm using a USRP and the usrp_rx_cfile program to record data for later
processing.  When I graph the recorded data, it looks choppy as if I
need to sample at a higher rate.  I have done a few runs at various
decimation rates and I'm confused by the resulting file sizes.  When I
set the decimation rate to 4, 8, or 16 for a constant period, the
resulting recordings are approximately the same size.  At decimation
rates of 32 or higher, the recording sizes reduce dramatically. I would
expect the recording sizes to increase inversely and proportionally to
the decimation rate.  The fact that this isn't happening makes me
suspicious of whether changing the decimation rate is really doing
anything.  I thought it might be that the USB throughput was the
limiting factor when decimation rates we low, but I tried recording
shorts rather than floats to reduce bandwidth usage, but I saw the same
results.  What am I missing?