On 03/22/2019 09:39 AM, Paul Boven via USRP-users wrote:
Hi everyone,
We recently did VLBI observations centered at 1332.49 MHz, using a
X310 with TwinRX. The USRP was locked to external references for 10MHz
and PPS for this. To get the best phase noise, I used 'integer-N'
tuning. We noticed that overall, our receiver frequency was off by
0.118 Hz. This causes the phase of the recorded signal to rotate in
about 9 seconds, compared to the other stations participating.
As far as I understand, when using integer-N tuning, the DDC simply
takes care of the remaining offset. What would be the tuning
resolution of the TwinRX itself (using int-N), and what is the
resolution of the DDC which corrects for this?
Regards, Paul Boven.
Another approach would be to simply modify your flow to apply the
frequency/phase correction prior to correlation.
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