[time-nuts] Measuring ADEV using TBolt-Tic tester

Tom Van Baak tvb at LeapSecond.com
Fri Oct 7 20:41:40 UTC 2011

> Long term, really low noise is all about the quality of the GPS signal and 
> engine.

And the antenna, and the multi-path, and ionosphere, etc. ...

With a Z3801A or TBolt (or any cheap single channel GPS) receiver
you should expect maybe a 5 to 10 to 15 ns variation over a 12 or 24
hour period. You should be able to see this with a 5065A or a good
Cs reference.

> The Z3801's GPS engine is far inferior and not even close to the 10 to 100 
> ps, 1 sec noise that a Tbolt engine has.

Careful, each does averaging. So to compare you have to include
the time constant into the equation. The RS232 numbers the TBolt
reports are heavily averaged so at 1 second they always look a lot
better than they actually are. If you have hard data for your claim,
I'd be interested in seeing it.


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