class fmDemodulator(object):
def __init__(self, sdr=None):
self.sdr = sdr if sdr else RtlSdr(device_index)
def demod(self, *args):
Fs = self.sdr.sample_rate
# Read IQ samples
samples = self.sdr.read_samples(256*1024)
print(samples)
# Convert sampled data into numpy array
x1 = np.array(samples).astype("complex64")
# Downmixed Baseband Signal (Adjust offset to be centered)
offsetFreq = 0 # already centered
fc1 = np.exp(-1.0j*2.0*np.pi* offsetFreq/Fs*np.arange(len(x1)))
x2 = x1 * fc1
# Filter and downsample the FM Radio Signal
bwFM = 200000 # approx. 170 kHz for a single channel
decRate = int(Fs/bwFM)
x3 = signal.decimate(x2, decRate)
newFs = Fs/decRate
### Demodulate 200kHz FM Signal
# Polar discriminator
y4 = x3[1:] * np.conj(x3[:-1])
x4 = np.angle(y4)
# The de-emphasis filter
# Given a signal 'x4' (in a numpy array) with sampling rate newFS
d = newFs * 75e-6 # Calculate the # of samples to hit the -3dB point
x = np.exp(-1/d) # Calculate the decay between each sample
b = [1-x] # Create the filter coefficients
a = [1,-x]
x5 = signal.lfilter(b,a,x4)
# Find a decimation rate to achieve audio sampling rate between 44-48 kHz
audioFreq = 44100.0
dec_audio = int(newFs/audioFreq)
audioFs = newFs/dec_audio
print(audioFreq)
x6 = signal.decimate(x5, dec_audio)
# Scale audio to adjust volume
x6 *= 10000 / np.max(np.abs(x6))
return x6, audioFs
def start(self):
while True:
x6, audioFs = self.demod()
sd.play(x6, audioFs)
return
def main():
sdr = RtlSdr(device_index)
fm = fmDemodulator(sdr)
# SDR Configurations
sdr.sample_rate = int(2.4e6) # Hz
sdr.center_freq = int(102e6) # Hz
sdr.freq_correction = 77 # PPM +- 20
sdr.gain = 'auto'
fm.start()
# Clean up
sdr.close()
del(sdr)
if __name__ == '__main__':
main()
提前谢谢!
