trial to build sna with rtl2832u dongle and pll synthesizer

sna-test.py

#!/usr/bin/env python
from adf4351usb import ADF4351
import numpy as np
import rtlsdr
import time

import matplotlib.pyplot as plt
import scipy.fftpack as sf

#start = 390e6
#end = 410e6
#step = 0.5e6
start = 400e6
end = 500e6
step = 1e6

def inclusive_range(x, y, s):
  while x <= y:
    yield x
    x += s
    
SAMPLE_RATE = 2e6
GAIN = 0

READ_SAMPLES = 65536
N_SAMPLES = 2048  # 1ms
PICKUP_OFFSET = READ_SAMPLES-N_SAMPLES
FREQ_CAL = -53.0e-6
FREQ_OFFSET = 5e3

window_func = np.hamming(N_SAMPLES)


def rtl_setup():
    rtl = rtlsdr.RtlSdr()
    rtl.set_sample_rate(SAMPLE_RATE)
    rtl.set_gain(GAIN)
    rtl.set_manual_gain_enabled(True)
    return rtl

pll = ADF4351()
rtl = rtl_setup()

#pll.setFrequency((start+end) / 2)

def measure(f):
  pll.setFrequency(f + FREQ_OFFSET)
  rtl.set_center_freq(f * (1.0 + FREQ_CAL))
  time.sleep(1)
  samples = rtl.read_samples(READ_SAMPLES)
  samples = samples[PICKUP_OFFSET:PICKUP_OFFSET+N_SAMPLES]
  #print samples

  pow = np.sum(np.absolute(samples)**2)/N_SAMPLES
  print "%g %g %g"%(f,pow,10 * np.log10(pow))
  return pow

def measure_fft(f):
  pll.setFrequency(f + FREQ_OFFSET)
  rtl.set_center_freq(f * (1.0 + FREQ_CAL))
  #time.sleep(0.5)
  samples = rtl.read_samples(READ_SAMPLES)
  samples = samples[PICKUP_OFFSET:PICKUP_OFFSET+N_SAMPLES]

  fourier_val = sf.fft(samples * window_func) / N_SAMPLES
  pow = max(abs(fourier_val))

  print "%g %g"%(f,pow)
  return pow

#np.arange(start, end, step)
freq = list(inclusive_range(start, end, step))
measured = [measure(f) for f in freq]
rtl.close()

#for f in freq:
  #pow = measure(f)
  #print "%g %g %g"%(f,pow,20 * np.log10(pow))

plt.xlabel("Frequency(Hz)")
plt.ylabel("Amplitude(dB)")
plt.plot(freq, 20 * np.log10(measured), "-")
plt.ylim(-60, 0)
plt.show()

File "./sna-test.py", line 41, in
pll = ADF4351()
File "adf4351usb.py", line 122, in init
h = hid.device(0x0456,0xB40D)
File "hid.pyx", line 45, in hid.device.cinit (hid.c:1351)
IOError: open failed