[time-nuts] GPS 18 behavior
David McGaw
n1hac at alum.dartmouth.org
Sun Jul 21 10:15:46 EDT 2013
The GPS-18 does NOT output 1PPS until it acquires lock. Then the 1PPS
stays on even if lock is lost, running from the internal crystal. I
have not checked, but once it reacquires lock I presume it jumps to the
correct second. All outputs including 1PPS are CMOS levels, so it
drives both low and high.
David
On 7/21/13 9:02 AM, Jim Lux wrote:
> 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.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts
mailing list