[Discuss-gnuradio] Using GNU Radio to accumulate FFT samples over a constant time duration before writing to disk

[Terrance Pat]

Hi everyone,

I am working on a project that requires the use of the USRP B210
and GNU Radio to act as a receiver and record signals being
transmitted from a RF source.

Initially, I thought it would be as simple as just taking the UHD_USRP
source and piping it to the file sink. However, it becomes apparent
the file holding the raw data quickly becomes very large; on the order
of gigabytes in a matter of minutes. It is expected that the receiver
will be collecting data for several hours and our disk space in the
receiver system is rather limited.

One person suggested having the software
accumulate or integrate the data samples after they've been FFTed for
a predetermined duration of integration time before writing to disk to
reduce the amount of overhead.

In the attached flight_recorder.grc file, I insert an integration
block between the USRP source and the file sink to do this, but using
the flight_recorder_playback.grc to play back the signal shows that
the sample rate is significantly reduced. Initially I thought
decimation had something to do with the time duration the integration
is done with the samples, but that was not the case and further
research showed decimation is defined as reducing the sampling rate.

I also tried the same approach in the attached flight_record_fft.grc
flow graph with the difference being I pipe the raw data to the FFT
block before running it through the integration block and writing to
disk.

Accumulating the data for some integration time should increase my
signal to noise ratio, but that is not happening with my current
approaches and there doesn't seem to be a way to tell the integration
block to integrate over a constant time duration. Perhaps I
misunderstood how the integration block works in GNU Radio.

Is there another approach using standard blocks in GNU Radio for
accumulating the FFTed data samples from a USRP source over a constant
integration time before writing to disk?

I am a novice when it comes to GNU Radio and any assistance is much appreciated.

Thanks,
-- 
Terrance

flight_GR_spectrum_analyzer.grc
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flight_recorder.grc
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flight_recorder.py
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flight_recorder_fft.grc
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flight_recorder_fft.py
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flight_recorder_playback.grc
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flight_recorder_playback.py
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flight_spectrum_analyzer.py
Description: Text Data