Plot spectrum of SigMF recordings

plot_spectrum.py

#!/usr/bin/env python3

import json
import pathlib

import numpy as np
import matplotlib.pyplot as plt


def main():
    NFFT = 2048
    N = NFFT * 4096
    files = pathlib.Path('.').glob('*.sigmf-data')
    
    for file in files:
        with open(file.name.replace('sigmf-data', 'sigmf-meta')) as f_meta:
            meta = json.load(f_meta)
        fs = meta['global']['core:sample_rate']
        x = np.fromfile(file, 'int16', count=2*N)
        x = x[::2] + 1j * x[1::2]
        f = np.fft.fftshift(np.average(np.abs(np.fft.fft(x.reshape(-1, NFFT)))**2, axis=0))
        freq = np.fft.fftshift(np.fft.fftfreq(NFFT, 1/fs))
        plt.figure()
        plt.plot(1e-6 * freq, 10*np.log10(f))
        plt.title(file.name.replace('.sigmf-data', ''))
        plt.ylabel('PSD (dB)')
        plt.xlabel('Baseband frequency (MHz)')
        plt.savefig(file.name.replace('sigmf-data', 'png'))


if __name__ == '__main__':
    main()