93 lines
2.7 KiB
Python
93 lines
2.7 KiB
Python
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import SoapySDR
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import numpy as np
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from scipy.signal import blackmanharris
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import serial
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fs = 5e6
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base_freq = 1086e6
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threshold = 0.4
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target_freq = 1088.3e6
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k = 200e-6
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induction_min = 430e3
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induction_max = 445e3
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generator = serial.Serial("/dev/ttyUSB0", 57600, writeTimeout=0)
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def set_induction_freq(freq):
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command = ":s1f{:010d}\n".format(int(freq*1e2))
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generator.write(command.encode())
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generator.readline()
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def set_induction(amount):
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amount = max(min(amount, 0.5), -0.5)
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freq = (induction_min + induction_max)/2 + amount*(induction_max - induction_min)
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set_induction_freq(freq)
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def parabolic(f, x):
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"""Quadratic interpolation for estimating the true position of an
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inter-sample maximum when nearby samples are known.
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f is a vector and x is an index for that vector.
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Returns (vx, vy), the coordinates of the vertex of a parabola that goes
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through point x and its two neighbors.
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Example:
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Defining a vector f with a local maximum at index 3 (= 6), find local
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maximum if points 2, 3, and 4 actually defined a parabola.
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In [3]: f = [2, 3, 1, 6, 4, 2, 3, 1]
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In [4]: parabolic(f, argmax(f))
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Out[4]: (3.2142857142857144, 6.1607142857142856)
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"""
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xv = 1/2. * (f[x-1] - f[x+1]) / (f[x-1] - 2 * f[x] + f[x+1]) + x
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yv = f[x] - 1/4. * (f[x-1] - f[x+1]) * (xv - x)
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return (xv, yv)
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def fmt_range(x, m):
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pos = int(round(x*80/m))
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return " "*pos + "*"
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sdr = SoapySDR.Device()
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samples = np.array([0]*4096, np.complex64)
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sdr.setSampleRate(SoapySDR.SOAPY_SDR_RX, 0, fs)
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sdr.setFrequency(SoapySDR.SOAPY_SDR_RX, 0, base_freq)
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rxStream = sdr.setupStream(SoapySDR.SOAPY_SDR_RX, SoapySDR.SOAPY_SDR_CF32)
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sdr.activateStream(rxStream)
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decimation = 0
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try:
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while True:
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sr = sdr.readStream(rxStream, [samples], len(samples))
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if sr.ret != len(samples):
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print("!")
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continue
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freqs = np.abs(np.fft.fft(samples*blackmanharris(len(samples)))[0:len(samples)//2])
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for i in range(len(freqs)//100):
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freqs[i] = 0
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freqs[-i] = 0
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# https://gist.github.com/endolith/255291
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i = np.argmax(freqs)
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true_i = parabolic(freqs, i)[0]
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freq = 0.5 * fs * true_i / len(freqs)
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amplitude = freqs[i]
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if amplitude > threshold:
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actual_freq = base_freq + freq
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print("{:8.3f} {:6.2f} {}".format(actual_freq/1e6, amplitude, fmt_range(freq, fs/2)))
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induction = (actual_freq - target_freq)*k
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else:
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print("<no signal>", amplitude)
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induction = 0.0
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decimation += 1
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if decimation == 15:
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set_induction(induction)
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decimation = 0
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finally:
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sdr.deactivateStream(rxStream)
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sdr.closeStream(rxStream)
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