Hi Piotr,
we once had a very similar issue. But we also saw this on the same
frequency when switching between frequencies. Can you try this as well?
Just switch forth and back between two frequencies and just plot one of
them?
As far as I remember the issue was because we were not using the
LO-Sharing. We were able to get everything running by using a C++
application and not gnuradio (I can see you are using python - which is
basically the same). There was a bug in gnuradio/python causing this issue.
You can try to remove one of the LO-sharing cables while doing a
measurement and see if the phase suddenly starts to do crazy things (the
signal should also be lost). If that is not the case, you are not
actually using LO-sharing.
Best regards,
Fabian
Am 03.04.2019 um 10:40 schrieb Piotr Krysik via USRP-users:
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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