Connecting a CDA-2990 to Multiple USRP-2945/2955

Updated Nov 7, 2023

Reported In


  • USRP-2945
  • CDA-2990
  • USRP-2955

Issue Details

I have a CDA-2990 and two USRP-2945s.or USRP-2955s. I would like to synchronize my application so I can receive on all eight channels across both of my USRPs. How do I connect the CDA-2990 to the USRPs, and how can I share the local oscillator (LO) between each USRP?


The CDA-2990 provides eight 10MHz clock outputs and eight PPS signals. Connect one of these 10MHz outputs to the REF IN connector on the back of each USRP you are using. Also connect one of the PPS OUT to the PPS TRIG IN on the back of each USRP. This ensures that all USRPs are looking at the same clock source, and it allows synchronization of the USRPs.

Each USRP-2945/2955 also has two LO OUT connectors (IF 1 and IF 2). These should be connected to the corresponding LO IN connectors on the second USRP. If additional USRPs are being used, this connection can be daisy-chained. For example. connect LO OUT of the first USRP to LO IN of the second USRP. Then connect LO OUT of the second USRP to LO IN of the third USRP, and so on. 

If you are using a USRP-2945/2955 to supply LOs to other USRP-2945/2955 devices, you may require power amplification. 
Using LO Reimport, the connections for Multi-Device Reimport LO Configuration are:

  1. Connect the USRP-2945/2955 (master) LO OUT 1 IF2 back panel connector to an RF power amplifier IN connector using an SMA(m)-to-SMA(m) cable.
  2. Connect the RF power amplifier OUT connector to a four-way RF power splitter.
  3. Connect the four RF power splitter RF output connectors to the LO IN 0 IF2 and LO IN 1 IF2 back panel connectors of all USRP-2945/2955 devices.
  4. Repeat steps 1 through 3 using a separate RF amplifier and RF power splitter to reimport and share the IF1 signal.
  5. Share a common reference and PPS signal between the USRP devices using a clock distribution device CDA-2990.
Example configuration may use Mini Circuits ZFRSC-4-842+ RF Power Splitter and PXI-5691 RF Amplifier.

Additional Information

For additional information on LO sharing and synchronization with the USRP-2945 and USRP-2955, please refer to Can I Share LO Between Multiple USRP-29X5?