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Re: [Discuss-gnuradio] Reading I & Q from a binary file


From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Reading I & Q from a binary file
Date: Sun, 25 Jun 2006 19:47:06 -0700
User-agent: Mutt/1.5.9i

On Sun, Jun 25, 2006 at 10:49:03PM +0000, paul munro wrote:
> Hi.
> I have sampled a FM signal and saved it to a file using 'usrp_rx_cfile.py'. 
> I have checked the file by demodulating it using 'wfm_rcv_file.py' and 
> everything works fine. I am now trying to read the file using LabView. The 
> tutorial by Dawei Shen says the data is 16 bit signed integers in I 
> followed by Q format. What I read in LabView is: each I sample is zero, and 
> Q values range from 0 to +-32000 (see figure).

The output of usrp_rx_cfile depends on the command line options you
use.  It saves files either with 16-bit I & Q, or 32-bit float I & Q 
(complex<float>).
By default it writes complex<float>.

> Are these values reasonable?? Should the inphase sample be zero?? I doesn't 
> seem right to me... Is it definitely I followed by Q, am I a word out??  I 
> have tried with a few different files, but I get the same results.

No, this doesn't sound reasonable.  It's highly unlikely that every
other sample is zero.

If you are expecting 16-bit I & Q, try using usrp_rx_cfile with the -s
command line option.  

FYI, most of the examples understand --help.  E.g.,
  

    address@hidden usrp]$ ./usrp_rx_cfile.py --help
    audio: using audio_alsa
    usage: usrp_rx_cfile.py: [options] output_filename

    options:
      -h, --help            show this help message and exit
      -R RX_SUBDEV_SPEC, --rx-subdev-spec=RX_SUBDEV_SPEC
                            select USRP Rx side A or B (default=A)
      -d DECIM, --decim=DECIM
                            set fgpa decimation rate to DECIM [default=16]
      -f FREQ, --freq=FREQ  set frequency to FREQ
      -g GAIN, --gain=GAIN  set gain in dB (default is midpoint)
      -8, --width-8         Enable 8-bit samples across USB
      --no-hb               don't use halfband filter in usrp
      -s, --output-shorts   output interleaved shorts in stead of complex floats
      -N NSAMPLES, --nsamples=NSAMPLES
                            number of samples to collect [default=+inf]

Eric




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