Re: [Discuss-gnuradio] Multiple USRPs

[Matt Ettus]

> 
> This raises a question I've always had about phase-coherence of PLL
> oscillators that use a common
>  clock source.  Will they be coherent "enough" for things like
> astronomical interferometry?

Yes.

> The individual PLLs will still have "close in" phase noise components
> that are unrelated to
>  on another.  I suppose that given that you typically integrate over
> several seconds, such
>  artifacts get cancelled out.  But at very fine timescales, I imagine
> that PLLs locked to
>  a common clock are *not* a good way to get decent coherency?

The close in noise is from the COMMON reference, so there is nothing to
cancel, it is perfect.  It is the further out phase noise components
which are not the same between the 2 PLLs, since those components are
from the individual VCOs.  These integrate out fairly quickly, and are
much smaller anyway.

Matt