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

John Ackermann N8UR jra at febo.com
Mon Mar 14 14:12:30 EST 2005

Hi Tom --

I am logging the lab temperature at 
http://www.febo.com/geekworks/therm.html and although I haven't done a 
careful correlation, I don't think the temperature change is aligned 
with the phase shift, particularly the sharp upticks that happen daily.

I'm not monitoring voltage (but I could...).  The Z3801A is powered from 
one of those 48V UPSs that were floating around last year -- basically, 
just 4 gel-cells with a float charger and some control circuitry across 
them.  The external divider and the 5370B are powered from UPS, though 
I'm not certain off the top of my head whether the UPS is always 
filtering, or is a switch-over type.  The reference for the 5370 is the 

I wonder if the Z3801A has the same PPS stability as the 58503B.  You 
mentioned the 58503B 1 PPS jitter was spec'd at some number of 
picoseconds.  When I've looked at both my Z3801As, I see about 30-50ns 
of peak-to-peak noise (with 100 second averages and logging times of up 
to several days; one unit is a bit quieter than the other).


Tom Van Baak wrote:
> John,
> Are you logging your lab temperature and mains
> voltage? Your plot continues to intrigue me.
> So I started a 53132A TI test between the 1 PPS
> and the 10 MHz outputs of my main HP 58503B
> GPS SmartClock (which is similar enough to a
> HP Z3801A for a first test, at least).
> While your plot shows about 1 ns ramp over half
> a day mine so far is flat; the 5 minute averages
> have a standard deviation of 15 ps. Plot attached.
> I'll switch to using a Z3801A and 5370B like you if
> necessary but again 1 ns over a day smells like a
> tempco or  voltco - in either the Z3801A or 5370B.
> /tvb
> http://www.LeapSecond.com
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