[Discuss-gnuradio] voltage pulse from UHD driver

[Anderson, Douglas J.]

Hi all,

I've been slowly working to understand/isolate an issue with a strange voltage pulse at all freqs and on USRP N210 with 50 Ohm load. 

I posted about it on StackExchange here, and there are more details at this link: http://stackoverflow.com/questions/27968237/semi-consistent-voltage-pulse-from-usrp-when-using-simple-gnu-radio-flowgraph

Since then, I've further isolated it as a UHD issue by completely removing the GNU Radio scheduler from the equation and simply using the finite_acquisition function on UHD to pull samples directly into Python.

Here is the code I'm using to produce this output http://i.imgur.com/c3YWA22.png:

An interesting thing is that when using the UHD driver is used outside a flowgraph (uhd.finite_acquisition), I get the strange pulse consistently, whereas when used in a flowgraph it was inconsistent (see the StackExchange question).

import numpy as np

import matplotlib.pyplot as plt

FREQ = 800e6

RATE = 1e6

NSAMPS = 100

usrp = uhd.usrp_source(device_addr="", stream_args=uhd.stream_args('fc32'))

usrp.set_center_freq(FREQ)

usrp.set_samp_rate(RATE)

fig, (freqplot, timeplot) = plt.subplots(2, sharex=True)

freqplot.set_title("Frequency domain")

timeplot.set_title("Time domain")

def plot():

    data = "">

    shifted_fft = np.fft.fftshift(np.fft.fft(data))

    dBm = 20*np.log10(np.abs(shifted_fft)) - 30

    freqplot.plot(dBm)

    timeplot.plot(np.abs(data))

def run_tb(times=25):

    for _ in range(times):

        plot()

    plt.show(block=False)

Douglas Anderson | Intern

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