Power Spectrum Not Stable When Using Simple Tx and Rx Streaming Example

Updated Mar 14, 2022

Reported In

Hardware

  • USRP-2944

Software

  • LabVIEW

Issue Details

I am using USRP-2944 with Simple Tx and Rx Streaming example to measure the power spectrum, the Tx channel will generate a finite signal and the Rx channel will measure the output signal from the same USRP. I found out that the result for the power spectrum is not stable at the Rx channel, I have tried many times by changing the USRP device, RF channel, central frequency, and transmit power, but the same issue happen. 
 
USRP.jpg

Solution

The issue cause by the wrong Rx trigger setting if you generate Tx signal in a finite mode. If the Tx and Rx did not sync well or not used the same trigger resource, Rx will fetch incorrect IQ data so the power spectrum result will become unstable. To sync Tx and Rx ports you need to set the start trigger as Tx Start Trigger in Rx Configuration. 
 
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