[time-nuts] HP Z3801A Question

SAIDJACK at aol.com SAIDJACK at aol.com
Thu Nov 13 18:10:33 EST 2008

Hello Ernie,
Glad your HP is still working well.
Well it seems you found out how well the Fury is working with an excellent  
The unit running in Mexico achieves similar performance with our standard  
double oven OCXO, see for example:
It has not jumped in several days, and the standard deviation is between  
1.7ns to 1.8ns when it doesen't jump during the last 24 hours.
Yes, the TI as displayed by GPSCon is much better than the HP  unit. I think 
this is mostly due to the much better GPS receiver in the Fury,  since the 
OCXO of the HP unit is extremely good.
Tom and I had discussions about this being caused by the small  sawtooth 
low-pass filtering we do on the TI intervall (Z3801A does the same  thing, 
otherwise you would see the full GPS Sawtooth). The theory was that this  was what 
was causing the Fury to be so much better on GPSCon.
To check this, we modified the firmware to completely remove this sawtooth  
filtering, and output the raw data instead, with all the nasty sawtooth  
artifacts on it.

This did not change the result much, I think the max range went from  +/-10ns 
to +/-15ns if I remember correctly.
So even if we display true raw capture data, we are still significantly  
better than the Z3801A which displays low-pass sawtooth filtered data.
I think this can mostly be attributed to the extremely good  performance of 
the M12M GPS compared to the Oncore GPS in the HP unit.
Also, I think you will see that your HP unit will get better over time, as  
the Crystal retraces and ages over the next weeks, and the control voltage  
changes will hopefully get to be smaller and smaller on your unit.
In a message dated 11/13/2008 14:38:57 Pacific Standard Time,  
ernieperes at aol.com writes:

But both  unit , the HP and the FURY board running under the same 
software  simultaneously / GPS Con / and I was mentioning the same small 
"windows"  TI to GPS, and the FURY displays much better figures then 
HP.....but  probably each units gives out / display / different 
Also the  graphic display / BLUE / on the FURY board the max ampl 
between +2,2nsec  and -2,0nsec sometimes +0,7nsec ,
the HP unit never goes  under +15nsec and -20nsec...... almost 10 times 
Anyhow I am  happy because it seems to me that the HP is still OK after 
3 years of  sleep.....

Rgsa Ernie.

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