Can I Share LO Between Multiple USRP-29X5?

Updated May 25, 2018

Reported In


  • USRP Software Defined Radio Device
  • USRP Software Defined Radio Reconfigurable Device
  • USRP-2945
  • USRP-2955


  • LabVIEW Communications System Design Suite
  • LabVIEW Communications MIMO Application Framework
  • LabVIEW



Issue Details

I'm currently using an USRP-2945 and I know that it can share local oscillator(LO) between two daughter-boards in itself. 
Is it possible to share LO between multiple USRPs?


The USRP-2945 and USRP-2955 both have independent receiver channel that support LO sharing for phase coherency. It's possible sharing LO between different devices if your test environment satisfies several conditions. Full signal based synchronization using the USRP-29X5 needs 3 signals:
  1. PPS Trigger
  2. 10MHz Reference Clock
  3. Local Oscillator (LO) (power amplified)
To specifically answer why you need the PPS Trigger, it is used to ensure that data is actually generated starting at the same time. Like in tclk, the USRP sends out a sync pulse, when a USRP receives the PPS Trigger it knows that it needs to start generating or acquiring on the next 10MHz clock edge.

The LO output port only provides enough power to drive a single TwinRX daughterboard.
So, external splitting and amplification of the LO output signal is required to drive any other TwinRX device.

Additional Information

If you use CDA-2990(Octoclock), the 10MHz clock and the PPS can be supplied by it, which makes the wiring and configuration a lot easier. However, they still need to use a PA and splitter to correctly route the LO.