[time-nuts] GPS 18 behavior

[Jim Lux]

I don't have a GPS-18 in front of me, and I'm modifying some software 
remotely, and I ran across an issue that someone on this list probably 
knows off the top of their head.

Does the GPS-18 put out 1pps pulses even if it hasn't got a fix yet? 
That is, when you apply power, does it just start putting out 1pps 
pulses (at some random phase), and then when it gets a fix, it snaps to 
the correct timing.

The manual says that it puts out 1pps pulses until power is removed, so 
I assume that when the GPS signal goes away, it keeps on as best it can. 
  I would assume that the clock isn't great, but it's reasonably close 
to 1pps.

What's the behavior when it reacquires?  Say the free-running 1pps is 
something like 1.1 Hz, so in 10 seconds, we've got an extra 1pps. Does 
it then skip pulses, or what?

And a sort of background hardware question...

The manual is also not very forthcoming on the electrical 
characteristics.. is it a pull up with a switch pulling it down to 
ground? or does it source significant current? That is, if you wanted to 
"wire or" the output from the GPS-18 with another 1pps source, would it 
be "diodes" or "resistors" you'd use.