USRP-29xx Continuous Wave Received Signal Power Is Much Lower Than Expected

Updated Apr 2, 2019

Reported In

Hardware

  • USRP Software Defined Radio Device

Software

  • LabVIEW
  • LabVIEW Communications System Design Software
  • LabVIEW NXG

Issue Details

I'm receiving a Continuous Wave (CW) signal with a USRP-29xx device, but the received power is much lower (over -20dB) than when receiving a modulated tone.

Solution

NI-USRP devices filter receive channels to try and reduce interference or "bleeding" from the Local Oscillator (LO) signal. By default, the filter that does this is set to be approximately the same frequency as the LO, which also approximates the carrier frequency of the incoming RF signal. In the case of a CW tone, the carrier frequency is equivalent to the frequency of the signal, and so the LO filter removes much more of the signal that needs to be analysed.

The workaround for this is to manually set the LO frequency  to be slightly offset from the CW frequency that is being received. To do this, wire the relevant USRP task to a property node and use the Configuration:Advanced:LO Frequency property. 

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