From: Eric Blossom <address@hidden>
To: paul munro <address@hidden>
CC: address@hidden
Subject: Re: [Discuss-gnuradio] Reading I & Q from a binary file
Date: Sun, 25 Jun 2006 19:47:06 -0700
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