[time-nuts] Of rubidium life and piggy-bank anemia....

[Magnus Danielson]

From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Of rubidium life and piggy-bank anemia....
Date: Sun, 02 Dec 2007 09:36:14 +1300
Message-ID: <4751C5BE.9060806 at xtra.co.nz>

> This technique creates the issue of how to correct for the effects of
> deadtime.

If you only switches among the sources, then you don't have a dead time as
such, it is just the time between the samples. You can make measures between
N sources in a repeatable fashion with a normal 2-input TIC such that you get
measures between all sources. For instance, if you have 5 sources, it takes 10
measures to measure all sources against all others. You can set up them such
that you access each source so that you shift from one source to another and
then stay with that for the next measure. In the case of 5 sources each source
would be selected and de-selected twice in each cycle. If you use RF relays or
ECL muxes is a choice. For a PPS rate dividing down 5 or 10 MHz sources to
20 Hz would allow for smart edge-selection to ensure an in-window edge even
with slow drift relative the others.

Such a setup would give you PPS rate updates for TIC values between all sources
as straight measures (i.e. not indirect relative some other source, which would
only consume 4 measures for 5 sources). No dead-time.

When a slip from one 20 Hz cycle to another due to phase drift occurs, it can
be handled in the software post-processing.

The access-pattern would make the measures not perfectly fit as well as if you
had multiple TICs on the task, but it would mostly be an issue for taus near
tau0.

Cheers,
Magnus