[time-nuts] Looking for Wavecrest Visi

[Dr Bruce Griffiths]

SAIDJACK at aol.com wrote:
>  
>
> Hi Bruce,
>  
> My math is essentially their reference [4, p.26], and I did state  that I 
> don't know the exact interpolator, trigger, and  frequency-dependent noise 
> functions of the Wavecrest.
>  
> DTS-2075 is superior to the SR-620 and 53132A in time interval measurement,  
> especially for single-shot measurements (parameters from manufacturers data  
> sheets):
>  
> DTS-2075:
>  
>   +-25ps single shot accuracy, 3-sigma
>   800 femtoseconds resolution with 1 femtosecond LSB display
>  
> SR-620:
>  
> Relative errors:
>   <±(50 ps typ. [100 ps max.] +
> Timebase Error ×  Interval)
>  
> Absolute errors:
>  
>   <±(500 ps typ. [1 ns max.] +
> Timebase Error × Interval  +
> Trigger Error)
>
> 25ps single shot resolution (31 times worse than DTS)
>  
> 53132A:
>  
>   150ps resolution, at 100ps uncertainty (RMS) (187 times worse  resolution 
> than DTS units)
>  
> bye,
> Said
>   

Said

Your claim of 1E-13 resolution in 1 sec is not sustainable.
The counter has no better resolution in measuring the Allan Variance of 
a source than any other counter with a single shot resolution of 25ps.
If you read the paper I mentioned it should be clear that averaging 
doesn't improve the resolution when resolution when measuring the Allan 
variance of a source.
Although it may have better differential and integral linearity specs. 
However they appear to give no specs for thes linearity.
The claimed 800fs resolution after averaging is irrelevant for this type 
of measurement.

The Wavecrest instrument only has a single shot resolution of 25ps not 
as you claim 800fs (this is only achieved after averaging)

The above counters can only be compared for this purpose if their single 
shot resolution and linearity are known.

Bruce