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Re: [Discuss-gnuradio] signal recording and replay
From: |
Eric Blossom |
Subject: |
Re: [Discuss-gnuradio] signal recording and replay |
Date: |
Thu, 30 Aug 2007 08:05:29 -0700 |
User-agent: |
Mutt/1.5.9i |
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