[time-nuts] Re: 1 PPS question

[Lux, Jim]

On 8/28/21 10:25 AM, Robert DiRosario wrote:
> For GPS receivers that give 1 PPS output the spacing between pulses 
> is, obviously, very accurate.
> Are the pulses synchronized to something, like UTC seconds, or does it 
> vary from one
> manufacturer to another, or even one unit to another?

GPS seconds (which are very close to UTC, except for the fact that UTC 
is an ensemble time, which technically isn't available until it's been 
processed).

Your receiver documentation should say whether it's the rising or 
falling edge of the pulse.

Some receivers, just to make things exciting, generate the pulse by 
gating an internal clock, so at the nanosecond level, there's a 
variation due to the internal clock not being synced with GPS, but free 
running. Some receivers will tell you what the offset is in some data 
message. Or, it won't, and you have to measure it (or average over many 
seconds, which is what GPSDOs do).

A simple question you ask and it can lead you down such a rabbit hole 
with hanging bridges, steps, etc.