Re: [Discuss-gnuradio] Mixing two signals for Radar application.

[Marcus D. Leech]

Hi Marcus,

here is the flow graph and the output signals with movement across the antennae and without.

http://tinypic.com/r/a5et5k/8  (GRC flow)

http://tinypic.com/r/nbeq0k/8  (without movement)

http://tinypic.com/r/2s7dnye/8 (with movement)

Thank you.

Dimitris.

OK, so I looked at the flow-graph you posted.  There's a lot of confusion in there, it has a lot of "confusion per unit area" of flow-graph, so there's
  a list:

  o You're mixing sample-rates without doing any interpolation or decimation.  For example, slamming your 100ksps signal source into a USRP hardware
      source that will try to suck samples out at 20Msps.

  o You're trying to mix this 100ksps source with a USRP source running at 25ksps (which isn't a valid rate for any USRP that I'm aware of).

  o You're using a throttle block in a chain that includes hardware -- I'm *guessing* that you thought maybe it would do sample-rate conversion
      or something, but it isn't clear what your intention is here.

  o You're trying to generate a 1MHz signal source with a sample-rate of only 100ksps.  This violates Nyquist rather badly.

I think you need to understand what your bandwidth requirements are, and let that guide your sample-rate decisions.  If this is a CW radar, you
  don't need a lot of bandwidth, and thus, sample-rate.

You don't mention what USRP hardware you have, but in general, the sample-rate must be a proper integer fraction of the master-clock rate,
  and generally, the resulting decimation can be no higher than 512.  Some USRPs (B100, E1xx, B2xx) have variable master-clocks, so you
  can achieve a variety of different rates.

Further, my suspicion from all the above is that your current grasp of DSP techniques isn't all that solid--I could be wrong, but it *seems* that
  way from the flow-graph.  My suggestion would be to step back, trying to really understand what you want to do, and maybe curl up with
  a book on DSP *first*.   While "stumbling around" when you're just building RX flow-graphs with real hardware doesn't do any harm, doing the
  same with TX flow-graphs can get unwanted visits from the Federal Authorities in some countries....

-- 
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org