W dniu 03.04.2019 o 10:34, Piotr Krysik via USRP-users pisze: > 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 > The frequencies here are carrier frequencies that are being set for each channel. On each carrier frequency measurement is performed - with use of sine wave or noise signal. Sample rate was 2MS/s.
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