Signal recording and replay

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

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

On Thu, Aug 30, 2007 at 02:41:28PM +0200, Max Moser wrote:

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.

  1. Was this modification correct?
    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?

[[email protected] 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

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