USRP Noise at Center Frequency

Updated Apr 19, 2018

Reported In

Hardware

  • USRP Software Defined Radio Device

Driver

  • NI-USRP

Issue Details

I'm trying to acquire or transmit signal with an NI USRP at low power, and I'm seeing noise at my center frequency. What is this noise and how can I get rid of it?

Solution

Noise at the center frequency is often caused by the USRP's local oscillator (LO) leaking into the transmit or receive lines. This is a common behavior in many RF devices, and can be eliminated by shifting the LO frequency away from your RF center frequency.

The LO frequency is normally automatically set by the driver based off of your specified carrier or center frequency. However, there is a USRP property node you can use to explicitly set the LO to a frequency outside of your bandwidth of interest. Because of each device's physical architecture, the difference between the LO frequency and center frequency must be less than the device's full bandwidth.

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