Two synchronized USRPs receive the same sinewave emitted by another USRP, there is a random and obvious phase offset between the received signals of the 2 receivers

[Jay_c]

Hi, everyone!

First, I use one USRP as a transmitter to emit a sinewave (the signal is exp(j2*pi*f*t)), then  I use the external clock to synchronize two USRPs (both the Ref in and PPS in are connected to the clock) as receivers. As the receivers are synchronized and they are at the same distance from the transmitter, I thought the signal they receive should have an almost the same phase. However, in practice, the phase offset is quite big, and this problem really confuses me.

this is the received signals from 2 receivers.

[ErikL · Accepted solution]

Yes. What you observe is expected.

Near the bottof of this document read the secton "Phase Alignment vs. Phase Coherence"

http://www.ni.com/white-paper/14311/en/

And also, for aligned phase, see the following "Angle of Arrival Detection with NI USRP"

https://decibel.ni.com/content/docs/DOC-25716

Erik

[Jay_c]

Thank you, Erik! Your reply perfectly answers my question!

[Jay_c]

Hi,

Hi, Erik. I have seen the AOA demo, and I am curious about the receivers where the two antenna connectors are used as RX (one by wire while the other is wireless). However, when I go to see the NI USRP-2920 Block Diagram, I think the RF Switch can only switch to one direction, is that right to use these two connectors as RX at the same time?

And can the two connectors of  USRP-2921 be used as RX at the same time?(In my lab, I only have USRP-2921)

Thank you very much!!

[ErikL]

The AoA code only received from channel rx1 and never the second one by wire using the switch. The students were clever and treat the switch as an attenuator since it has leakage. You could accomplish the same using a T junction on Rx1 with 30db of attenuation in the cabled path.