Unexpected data readings from SoapySDR Python API

Hello all.

I am trying to capture some receiver samples using the Python API of SoapySDR. My code is based on the basic examples of https://github.com/pothosware/SoapySDR/wiki/PythonSupport and https://github.com/pothosware/SoapySDR/blob/master/python/apps/MeasureDelay.py.

In particular I have setup a receive stream active for 10240 samples, and read out bursts of 1024 samples. I am using CF32 precision and store the results in a Numpy Complex64 array. LimeSDR configuration and receive procedure seem to work fine, however when I am trying to see the actual data i get only a few discrete values containing a lot of 0s and the value -0.000488296151161. Checkout the attached snapshot:

(I expected typical noise samples)

I am certain that the device is working normally since i’ve tested it using GnuRadio. Initially I was working with the latest master version, but I got an “NodeMCU error” and downgraded to 17.12-1.

Has anyone observed similar behavior? I’ll give it a try using the C++ API as well.

Here is my Python code:

import SoapySDR
from SoapySDR import * #SOAPY_SDR_ constants
import numpy as np
import time
import os

numSamps = 10240
burstSize = 1024

#enumerate devices
results = SoapySDR.Device.enumerate()
for result in results: print(result)

#create device instance
#args can be user defined or from the enumeration result
args = dict(driver="lime")
sdr = SoapySDR.Device(args)

#query device info
print (sdr.listAntennas(SOAPY_SDR_RX, chan))

print "============================================="

#apply settings
print("Actual Master Clock Rate %f Msps"%(sdr.getMasterClockRate()/1e6))

sdr.setSampleRate(SOAPY_SDR_RX, chan, 1.92e6)
print("Actual Rx Rate %f Msps"%(sdr.getSampleRate(SOAPY_SDR_RX, chan)/1e6))

sdr.setFrequency(SOAPY_SDR_RX, chan, 1.9e9)
print("Actual Rx Freq %f MHz"%(sdr.getFrequency(SOAPY_SDR_RX, chan)/1e6))

print("Antenna on Channel %i is %s"%(chan,sdr.getAntenna(SOAPY_SDR_RX,chan)))

print("Actual Rx Gain %f "%(sdr.getGain(SOAPY_SDR_RX, chan)))

#sdr.setBandwidth(SOAPY_SDR_RX, chan, 3.84e6)
#print("Actual Rx BW MHz %f "%(sdr.getBandwidth(SOAPY_SDR_RX, chan)/1e6))

#sampleRates = sdr.getSampleRateRange(SOAPY_SDR_RX, chan)
#for srRange in sampleRates: print(srRange)
print "============================================="

#create rx stream
rxStream = sdr.setupStream(SOAPY_SDR_RX, SOAPY_SDR_CF32, [chan])

#let things settle

#start streaming
sdr.activateStream(rxStream, 0, 0, numSamps)

# buffer for storing accumulated samples
rxBuffs = np.array([], np.complex64)
#create a re-usable buffer for rx samples
rxBuff = np.array([0]*burstSize, np.complex64)

#receive some samples
while True:
    sr = sdr.readStream(rxStream, [rxBuff], len(rxBuff))
    print(sr.ret) #num samples or error code

    #stash time on first buffer
    if sr.ret > 0 and len(rxBuffs) == 0:
        rxTime0 = sr.timeNs
        if (sr.flags & SOAPY_SDR_HAS_TIME) == 0:
            raise Exception('receive fail - no timestamp on first readStream %s'%(str(sr)))

    #accumulate buffer or exit loop
    if sr.ret > 0:
        rxBuffs = np.concatenate((rxBuffs, rxBuff[:sr.ret]))
    else: break

#cleanup streams
print("Cleanup streams")
sdr.deactivateStream(rxStream) #stop streaming

# process data
print len(rxBuffs)
print("Captured %i samples in total"%(len(rxBuffs)))
print np.real(rxBuffs[10000]),np.real(rxBuffs[10001]),np.real(rxBuffs[10002])
# dump samples
#np.savetxt('outfile.txt', rxBuffs,'%.10f\t%.10f')

I didn’t use soapy. Instead, I am using ctypes for Python to call directly the functions from limesuite.so.

Everything works fine. I realized a simple spectrum analyzer.

You can use https://github.com/roger-/pyrtlsdr as a reference. The idea is the same.