[time-nuts] HP Z3801A info needed - 1PPS interface

[ed breya]

I've been doing a bit more work on the far from finished Z3801A project, 
trying to button things up. It has been sitting for years all opened up 
(but running), with temporary pieces and cables and wiring hanging out 
every which way. The next piece I want to get going is the 1 PPS 
interface, to provide the signal out, and to run the clock. In the 
manual it says the 1PPS signals are on the DB-25 connector, in 
differential "pseudo-ECL" form, but that's all - no level or common-mode 
info is provided. Online searching the term seems to indicate it's just 
PECL - Positive ECL running from +5 V, with everything shifted up 
accordingly. That's just fine (and easy to implement), as long as I know 
what to expect. I figured I'd check here to see if that's correct, or if 
it means something else in the Z3801A context. I'll find out eventually 
when I start fooling with it, but right now it's buried deep in the guts 
of the box, so not easy to scope out yet until I start hooking it up and 
designing the interface.

A related question is, is there any particular generally accepted or 
favorite spec or description of the 1PPS signal output from the BNC? 
I'll probably make it 0/+5 V out, fairly strong, with the leading 
positive edge being the official tick mark. The clock will use a 
softened up version. The DF will be whatever the Z3801A puts out.

Ed