Re: [Discuss-gnuradio] signal recording and replay

[Eric Blossom]

On Thu, Aug 30, 2007 at 02:41:28PM +0200, Max Moser wrote:
> Hi there,
> 
> well gain i like to ask a short question. I did try to record some  
> signal in 27mhz. Its FM based.
> 
> I did it like this:
> 
> 1st i modified usrp_tx that it saves the recording into a file called  
> audio-0.dat
>       /usrp_rx_nogui_to_file.py -f 27.195M -g 20 -m FM (tried it with rate 
> 32000 and 48000)
> 2nd i try to replay the data using:
>       ./fm_tx4.py -f 27.195M -n 1

fm_tx4 FM modulates the given audio file.  It's not just "playing back
the samples"

You need to understand the difference between samples at IF and
demodulated audio samples.


> I did have my radio scanner beside of me and can say from the sound  
> allready that the signal is deeper. (Akkustically)
> so i guess its the samplerate. But no matter what i use it does not  
> seem to be right.
> 
> Just before i go nuts i hope that someone hase answers for the  
> following questions:
> 
> 1) Did i do it correctly? Is there a better way to save and replay a  
> signal? Can you give me an example?
> 2) Was this modification correct?
> 
>                       diff usrp_rx_nogui.py usrp_rx_nogui_to_file.py
>       153c153,154
>               <         AUDIO = audio.sink(options.output_rate, "")
>               ---
>               >         #AUDIO = audio.sink(options.output_rate, "")
>               >       AUDIO = gr.file_sink(gr.sizeof_float,"audio-0.dat")
> 
> 3) When i use ./usrp_rx_cfile.py -f 27.195M -g 20 --no-hb output.dump  
> i just get high frequent noise instead of the signal, thats why i  
> modified usrp_rx_nogui.
>      is there a way to record it using cfile corectly so i can replay?
> 
> Greetings
> Max

What sample rate are you expecting at the output of usrp_rx_cfile?
Since you haven't specified a decimation value you're going to get 16
which implies 4MS/s (64e6/16).  Is that what you want?
Also, why are you turning off the half-band?


address@hidden usrp]$ ./usrp_rx_cfile.py --help
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