[time-nuts] Fury Realhamradio listing

Peter Schmelcher nebula at telus.net
Mon Aug 20 05:24:50 EDT 2007

>C) I don't believe the Z3801A has 100ps single shot resolution and accuracy
>(for resolution doesn't do anything without accuracy) until someone will
>prove it to me. And even then it would be wasted resolution since the GPS 
>source noise will totally swamp out any benefit a 100ps resolution 
>would  give.

Hi Said,

I inadvertently measured the TI resolution of a Z3816A and it is a stable 
100ps.The setup was a slightly modified VP receiver that has a phase locked 
LO (a 3325A locked to the OCXO) which replaced the normal UT GPS receiver 
in the Z3816. The measurements were made during a "hanging bridge" when the 
GPSDO servo loop is effectively open circuit for phase errors smaller than 
the saw tooth. The HP motherboard then averages 5 GPS pps samples so I 
guess the servo loop has control resolution of 20ps.

A side effect of the 5 sample average is the opportunity to reduce the 
effective saw tooth error to 1/5 when the GPS LO is adjusted about 0.4 Hz 
high. This causes the GPS pulse position to advance about 20ns every second 
and repeat every 5 seconds creating a more stable average.


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