[USRP-users] Tuning resolution of TwinRX + DDC?

Paul Boven p.boven at xs4all.nl
Fri Mar 22 09:39:29 EDT 2019

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.

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