GNU Radio Manual and C++ API Reference  3.7.3
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UHD Interface

Introduction

This is the GNU Radio UHD package. It is the interface to the UHD library to connect to and send and receive data between the Ettus Research, LLC product line. To use the UHD blocks, the Python namespaces is in gnuradio.uhd, which would be normally imported as:

from gnuradio import uhd

The relevant blocks are listed in the UHD Interface group.

A quick listing of the details can be found in Python after importing by using:

help(uhd)

Documentation

Ettus Research keeps the comprehensive documentation to the underlying UHD driver, which can be found:

http://files.ettus.com/uhd_docs/manual/html/

The UHD Doxygen page is located:

http://files.ettus.com/uhd_docs/doxygen/html/index.html

Setup

A typical option parser setup for a UHD device looks like

parser = OptionParser(option_class=eng_option)
parser.add_option("-a", "--args", type="string", default="",
help="UHD device address args , [default=%default]")
parser.add_option("", "--spec", type="string", default=None,
help="Subdevice of UHD device where appropriate")
parser.add_option("-A", "--antenna", type="string", default=None,
help="select Rx Antenna where appropriate")
parser.add_option("-s", "--samp-rate", type="eng_float", default=1e6,
help="set sample rate (bandwidth) [default=%default]")
parser.add_option("-f", "--freq", type="eng_float", default=None,
help="set frequency to FREQ", metavar="FREQ")
parser.add_option("-g", "--gain", type="eng_float", default=None,
help="set gain in dB (default is midpoint)")

To use these options to create a UHD source object:

self.u = uhd.usrp_source(device_addr=options.args,
io_type=uhd.io_type.COMPLEX_FLOAT32,
num_channels=1)
self.u.set_samp_rate(options.samp_rate)
# if no gain was specified, use the mid-point in dB
if options.gain is None:
g = self.u.get_gain_range()
options.gain = float(g.start()+g.stop())/2
self.u.set_gain(options.gain, 0)
# Set the center frequency
self.u.set_center_freq(options.freq, 0)
# Set the subdevice spec
if(options.spec):
self.u.set_subdev_spec(options.spec, 0)
# Set the antenna
if(options.antenna):
self.u.set_antenna(options.antenna, 0)

Frequently, your application may need a sample rate that is not supported by the UHD device. If you have extra CPU power to spare, you can easily set the sample rate you want, then ask the device what the actual sample rate set was. Then, you can easily create an arbitrary resampler to take care of the difference.

self.u.set_samp_rate(options.samp_rate)
desired_rate = options.samp_rate
actual_rate = self.u.get_samp_rate()
resample = desired_rate / actual_rate
# Use the filter.pfb version and pass only the resample factor.
# This block builds a half-band filter for you
self.resampler = filter.pfb.arb_resampler_ccf(resample)