from rtlsdr import RtlSdr
from matplotlib import mlab

sdr = RtlSdr()

# configure device and settings
sdr.sample_rate = 2.048e6  # Hz
sdr.center_freq = 151e6     # Hz
sdr.gain = 'auto'
num_samples = 1024
threshold = -0.10 # empirically derived

my_samples = sdr.read_samples(num_samples)
magnitude_values, freqs = mlab.magnitude_spectrum(my_samples)

above_threshold = []
for index, magnitude in enumerate(magnitude_values):
    if magnitude > threshold:
        above_threshold.append([magnitude, freqs[index]])