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[Discuss-gnuradio] Really low sample rates for gr_sig_source_x()

From: Marcus D. Leech
Subject: [Discuss-gnuradio] Really low sample rates for gr_sig_source_x()
Date: Sat, 08 May 2010 18:13:15 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4

It looks like when you set low sample rates (say below 1KHz), the NCO
code doesn't seem to work right,
  *never* putting out samples.

I haven't done exhaustive testing.

This was prompted by Bill Pretty's issue with his flow-graph that uses a
triangle or sawtooth generator,
  at low sample rates (2Hz) and low Fc (a fraction of a Hz) to drive the
tuning variable going back into
  the USRP.

I tested the graph he gave, and after making a few fixes, observed that
the signal source appeared to be
  never producing any output.  Hmmmm.

So, I did up my own flow-graph, consisting of a signal source, a
throttle, and a number sink and scope.
  It only started to work when I cranked the sample rate up to about
1KHz on the signal source.

Any ideas?

Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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