[time-nuts] Frequency Ensemble

[Attila Kinali]

On Sun, 17 Mar 2019 10:58:49 -0400
Bob kb8tq <kb8tq at n1k.org> wrote:

> The first thing you need (after all the standards) is a way to do precision 
> comparisons of all your devices. There are an infinite number of ways to do
> this. Let’s say you buy 26 TICC’s to do the job ( TAPPR needs 25 ordered to
> get the next batch going so that would solve two problems at once :) ). A
> PPS from a single source with good short term stability (maybe an OCXO) goes
> into one side of all of them. A pps from a DUT goes in the other side (yes
> there are other ways …TAPPR needs that order ….).
> You then have 26 devices each reporting how a single standard compares to 
> the “main OCXO”. 


I would use here a variant of DMTD: Instead of comparing pairs
of standards, have one offset frequency generator feed multiple
mixers, one for each standard. This way, the standards can be
compared to eachother more easily. Downside of this is, that
the precision of this comparison depends on the stability of
the distribution of the offset frequency signal. Though, under
the assumption that ground loops can be kept in check, this
should be easier to ensure than having pair wise comparisons
not drifting away too much. When using TICCs, with their high
measurement rate, I would also go for an offset frequency in
the order of 1kHz instead of the customary 1-10Hz. This will
help getting away from the flicker noise region and also give
a much higher slope of the signal to work with, reducing the
white noise of the measurement. Additonally, this should
also give higher precision at tau = 1s, as the system is now
averaging down from 1ms instead of 100ms (when using 10Hz),
which could potentially give a boost of a factor of sqrt(100ms/1ms) = 10.

			Attila Kinali

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