[time-nuts] Common sky pps errors for any GPSDOs?

[Bruce Griffiths]

Matt Ettus wrote:
> I am working with someone who needs to have time synchronized
> reception of signals in various locations which are separated by less
> than 100 km.  This is a situation similar to VLBI, but since the
> distances are shorter, the center frequencies are lower, and the
> integration times are much shorter, we probably don't need a Hydrogen
> Maser, and the application can't afford one.
>
> The real question is whether we can get away with a GPS disciplined
> OCXO or whether we would need to use a Rubidium.  Does anyone have any
> data on the relative frequency and/or phase errors of the 10 MHz
> reference out, and relative PPS time errors of any commonly available
> GPSDOs?  Absolute error to UTC and true 10 MHz don't really matter, as
> long as both devices have the same error.  Just data comparing 2 units
> with antennas right next to each other would probably be fine.
>
> The other concern, of course, is that even if both units were very
> close, they will be exposed to slightly different environmental
> conditions (different A/C settings, different cycling times, etc.).
>
> Are there any good papers discussing this subject?  Any data out there?
>
> Said -- have you measured this sort of thing on the Fury?
>
> Thanks,
> Matt
>
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>   
Matt

If the application is somewhat analogous to VLBI, then the maximum
(uncorrectable ie random) allowable carrier frequency phase errors
between receivers depends on the integration time.
Maximum integration times for VLBI are typically 10,000 sec or less,
with corresponding relative ADEV (after correction for drift etc) on the
order of 1E-14 (or better) @ 10,000 sec for a carrier frequency of a few
GHz.

What is the integration time in your application?

What is the carrier frequency?

For short integration times most rubidium standards are much noisier
than a good OCXO.
GPS carrier phase techniques will allow lower noise comparisons of LO
phase differences than a GPS derived PPS based system.

Bruce