[time-nuts] How do time-nuts measure phase noise?

[Gerhard Hoffmann]

On Mon, 17 Aug 2009 23:18:58 +1200, you wrote:


>1) Use 3 sources, S1, S2 and X.
>
>2) Phase lock S1 in quadrature to X using a diode double balanced mixer
>using a low bandwidth PLL.
>
>3) Phase lock S2 in quadrature to X using a diode double balanced mixer
>using a low bandwidth PLL.
>
>Then for frequencies outside the PLL bandwidth the crosspower spectrum
>of the 2 mixer outputs should be predominantly due to the phase noise X.
>
>In practice its best if the phase noise of the 2 standards S1, S2 isn't
>significantly worse than that of X.
>
>It is also desirable that both S1 and X and S2 and X be locked at their
>respective mixers quadrature point (not necessarily the same as that for
>zero dc output)

Has anybody out there already written that cross correlation /
user interface stuff? I can / will build a neat multi channel digitizer,
perhaps with USB2, but trying to link it to Linux/Windows would probably 
make it a never ending story. 

BTW when building the DG8SAQ vector network analyzer 
<http://groups.yahoo.com/group/VNWA>  I had to learn that the sound system 
of my deLuxe Core Duo motherboard sports ridiculous 40 dB of channel separation. :-(

I would also like to try Inphi's sample&holds in front of a decent RF ADC 
for a direct RF three cornered hat implementation (maybe a ANSI/VITA 57 
mezzanine board for a contemporary Xilinx development board), 
but with all the software it's too much for one person.

I have done a new incarnation of my discrete NIST-flavoured distribution
amplifier. The input return loss still needs to be cleaned up, then
it's ready for publication.


Gerhard, DK4XP