[time-nuts] Looking for Wavecrest Visi

SAIDJACK at aol.com SAIDJACK at aol.com
Sat Apr 7 19:48:21 UTC 2007


 
In a message dated 4/7/2007 04:08:20 Pacific Daylight Time,  
cfmd at bredband.net writes:


The  Wavecrests are wonderful tools, but they address a different problem  
than
what normal time-nuts usually care about, so they are not a given  perfect
counter for long term comparision. It is aimed at jitter. 


Hi Magnus,
 
that's true for the SIA/SRT series of Wavecrest instruments.
 
But the DTS series (DTS-2070, 2075 etc) have features that your SRT does  not 
have, for example cable-length measurement with picosecond resolution.
 
The DTS units also have sophisticated external Arming features the SRT  
doesen't have (two ARM inputs).
 
They also have A to B time intervall measurements so one can do a DUT to  
Cs/Rb comparison for example with +-25ps accuracy per measurement, at 40000  
measurements per second. Visi allows long-term high-resolution drift plots that  
can be turned into ADEV plots.
 
Theoretically, this means +-25E-012 / rt(40000) = +-1.25E-013 measurement  
accuracy per second if it's internal accuracy-noise is gaussian (I am not sure  
it is)  so it would average out when comparing one 10MHz against  another 
10MHz source.
 
I don't have the Visi software so I cannot use the HiPer 40Ks/s option so  
the above remains theory until I can find the software.
 
Also, I don't think the SRT3000 can do two-input A to B  measurements if I 
remember correctly.
 
As of today, there is a DTS-2070 on Ebay (search for "Wavecrest Digital  Time 
System") for $900 buy-it-now from a known-good vendor.
 
In summary, I think the SRT is perfect for many-input parallel jitter  
analysis, while the DTS is more of a traditional time-intervall-analyzer  suitable 
for time-nuts usage. BTW: I think they both are not very good as true  
frequency counters.
 
bye,
Said



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