Issue Synchronizing TX and RX LO for Step Frequency Radar Using Single USRP X310

[cosmos123]

Hi,

I am working with two USRP X310s to implement a Step Frequency Continuous Wave (SFCW) radar in C++. My main issue is synchronizing the TX and RX LO frequencies.

The TX frequency hopping appears to work correctly. I verified the transmitted frequencies using a handheld VNA, and the hopping sequence is correct. However, I am not sure whether the RX LO is tuning to exactly the same frequency at the same time as the TX LO.

Is there any reliable method to verify that the TX and RX LOs are synchronized or to confirm that the RX is actually receiving the signal at the correct LO frequency?

I have also written code assuming that the TX and RX LOs are synchronized, but the measured target range changes every time I repeat the experiment, even when the target position is fixed. This makes me suspect that the LO synchronization or tuning timing is not correct.

Any suggestions on how to verify LO synchronization or debug this issue would be greatly appreciated.

[mikiofuku]

Hi, 
Are you synchronizing the two USRPs using an Octoclock to provide the 10 MHz reference clock and PPS signals, with the following arguments?

--args "addr0=192.168.x.x,addr1=192.168.x.x,time_source=external,clock_source=external"
Mikio