[time-nuts] HP Z3801A Question

SAIDJACK at aol.com SAIDJACK at aol.com
Thu Nov 13 16:41:13 EST 2008

Hello Ernie,
as Bjoern mentioned I think the HP is indicating Time Interval between GPS  
and OCXO 1PPS in nanoseconds, while the Fury is indicating estimated frequency  
accuracy, a unitless number.
The Fury is showing estimated average frequency error over the last 1000  
seconds, similar to AVAR 1000s.
You can run GPScon on Fury too, and should be able to compare against the  
graphic you did for the HP unit.
Or you could set the LCD of the Fury to show Time Interval to UTC, or probe  
this time interval to UTC with the command ptim:tint? that will return the  
offset in nanoseconds as well.
An offset of +/-50ns to UTC seems to be normal for the HP unit. On the  Fury, 
I would expect this to be +/-10ns on a good OCXO.
To the benefit of the Z3801A unit: if the HP unit indicates a larger  offset, 
it may also be because it's internal GPS is not as good as the Fury  GPSDO 
receiver. It does not necessarily mean the OCXO is causing the error, it  could 
be that the HP GPS is causing the error, and the HP OCXO is  still dead-on 
because it filters out its higher GPS errors.
In a message dated 11/13/2008 02:45:57 Pacific Standard Time,  
ernieperes at aol.com writes:

And  running parallel the FURY board with a TEMEX OCXO and displays 
+1,6E-10 is  the average very often 10E-11 and sometimes for a relative 
short time /  4-5 min / 1,4E-12.

Any idea why the Z3801A not displaying better  figure?? Something wrong 
with the HP unit????

Thanks  Ernie.

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