[time-nuts] Higher measurement rate to improve TIC quality?

[Magnus Danielson]

From: Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz>
Subject: Re: [time-nuts] Higher measurement rate to improve TIC quality?
Date: Sat, 21 Apr 2007 12:09:37 +1200
Message-ID: <46295641.3050305 at xtra.co.nz>

> Brooke Clarke wrote:
> > Hi:
> >
> > I'm still trying to understand Allan plots.  For example looking at a Time 
> > Interval Counter's stability.
> >
> > The one shot resolution of the Time Interval Counter is important since it 
> > determines the stability floor on an Allan plot.  Can the stability floor be 
> > improved by making the measurements faster?  That would move the one shot 
> > resolution point to the left thus moving the line down.
> >
> > For example if the one shot resolution of a TIC was 10 ns when measuring a 1 
> > PPS signal that defines a point at 1 second on the X-axis and at 10 ns on the 
> > Y-axis.  Now if the measurement can be made 10 times in each second (the test 
> > signal is changed to a 10 Hz square wave), then the point on the Allan curve is 
> > now a facter of 10 lower.
> >
> > Have Fun,
> >
> > Brooke Clarke
> >   
> Brooke
> 
> No, the resolution of the measurement for 1 cycle of a 10Hz square wave 
> is degraded to 1E-7 cf with 1E-8 for 1 cycle of a 1Hz square wave.

Recall, with 10 ns of singelshot resolution you have 100 000 000 counts each
second, where as you only have 10 000 000 counts on each of those 10 Hz edges.
They average to the same. Remember that tau is the distance between samples.
(Oh, Bruce corrected me indirectly, that's for being tired and his wording is
more correct). Thus, tau is you gate-time.

Cheers,
Magnus