Capturing Signals in GNU Radio (ZZ)

Storing Data into a File
The output of any block (including the USRP) can be stored into a data file. Insert the following commands into the Python script:

audiodata = gr.file_sink(gr.sizeof_float, “audio.dat”)
self.connect(src0, audiodata)

This creates a sink named audiodata which will store its data (binary) into a file called audio.dat. The sink is then connected to the source or block that will be outputting the data to be collected. In this example we have used src0 to represent a source. In the event that the source/block outputs complex data, use

audiodata = gr.file_sink(gr.sizeof_complex, “audio.dat”)



Converting the Binary File to a MATLAB Readable Form

The file created above contains binary data that MATLAB (or Octave) does not know how to read. There is a set of .m files in gnuradio-core/src/utils that perform the needed conversions. In the case of a binary data file that contains floating-point data use:
read_float_binary.m

In the case of a binary file that contains complex data use
read_complex_binary.m

From Octave you can run these with:
audio1 = read_float_binary(‘audio.dat’);

and the resulting data will appear in a matrix called audio1.


Plotting the Data with Octave
You can create a plot of this data in Octave (assuming Gnuplot is also installed) with:
plot(audio1)

Plotting the Data with MATLAB
If you would like to create a data file that is readable by MATLAB you need to save the audio1 data in a MATLAB readable file. This can also be done from within Octave using:
save (“-v7”, “audio2.mat”, “audio1”)

The file audio2.mat can now be imported into MATLAB (Mac or PC).