Hi all, I'm trying to do calibration of phase offsets between TwinRX channels.
Configuration of X310 is following: two TwinRX'es, all sharing LOs from fist channel of the second TwinRX. The same signal is fed to all TwinRX channels through a RF splitter. What is expected is some additional group delay for TwinRX that gets LO signal through a cable from the other TwinRX. This group delay was compensated by using longer RF cables between splitter and RF inputs of TwinRX1 that uses external LOs from TwinRX2. However, there is also unexpected effect: there are +/-90 degree phase difference changes between channels of one TwinRX1 and TwinRX2 in function of frequency. Measurements were performed between 100MHz and 500MHz, and here are the results: 1. 128MHz: +90 degrees 2. 172MHz: -90 degrees 3. 245MHz: +90 degrees 4. 260MHz: -90 degrees 5. 340MHz: +90 degrees Here is example plot of phase difference fom channel 1 (TwinRX1) to channels 2 and 3 (TwinRX2): https://imgur.com/4C09MSf What I would expect (after compensation of LO cable length) was something (~) flat, but there are these phase jumps by +/-90 degrees. This effect can be included in calibration. But it would be best to know: where these phase jumps for different frequencies come from? Best Regards, Piotr Krysik _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
