[time-nuts] Where does the Z3801A 1 PPS come from?

John Ackermann N8UR jra at febo.com
Sun Mar 13 11:51:05 EST 2005

I asked myself that question the other day and decided to see whether 
the 1pps was simply divided from the 10MHz frequency, or whether it was 
actively stepped.  So, I started an experiment with the time interval 
counter to compare the 1 PPS output* with a 1 PPS signal from an 
external divider on the 10MHz output.

Here are the results: http://www.febo.com/time-freq/plots/z3801a-pps.html.

There is about 2.5ns of peak-to-peak variation between the two (with 100 
second averaging, and measured over about 36 hours as I type this).  
That's not much, but there's an interesting very linear daily sawtooth 
pattern.  I have no idea what to make of it, other than it indicates 
some sort of active steering is going on separate from the oscillator 


* Picked off using Jeff Mock's hardware mod at 

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