[time-nuts] HP Z3817A Reverse Engineering

Ed Palmer ed_palmer at sasktel.net
Sun Jan 8 17:20:00 UTC 2012


I recently purchased a Motorola STLN4096A with the HP E1938A 
oscillator.  I bought it for the oscillator only.

Then I got intrigued by the HP Z3817A GPSDO that's included.  I've 
reverse engineered most of it and I've got it running.  The 1 PPS is 
really good ( 1000 measurements, Std. Dev. of <200 ps, min to max range 
of <1.5 ns) and the HUP is very slowly dropping (currently at 13 us 
after ~1.5 days) as the oscillator works out the kinks after it's long 
sleep.  It's dropping much slower than my Z3801A did when I first turned 
it on.

There's one input that I haven't been able to figure out.  I've got data 
in and 1 PPS in from the GPS receiver.  Everything seems to be working 
so I'm at a loss what that the other input could be for.  There are no 
clues to it's function because it appears to go into one of the Xilinx 
chips.

Does anyone have any more info on the unit?  Has anyone figured out the 
other input?

I have searched the net and the archives.  There's very little info or 
discussion on this unit.

Ed




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