[time-nuts] Turning off PPS when not enough satellites

[bg at lysator.liu.se]

On Tue, August 1, 2006 13:16, Ulrich Bangert said:
> Poul-Henning did already give the answer. However i am not very happy
> with the formulation

I do like Poul-Hennings forumulation better...

Lets go back to your orginal formulation

>> >> Note that any gps receiver can not be really good for
>> >> timing and navigation at the same time, so all navigation receivers
>> >> make bad timing receivers.

I know one country where the national timing laboratory uses the same
make/model GPS receiver as the cadastre service. There are probably
differences in which SW options are activated -- surveying guys might have
less interest in external frequency input/output. Here both the guys
defining national time AND the national geografic reference system can use
the same receiver.

Most navigation receivers are surely "bad" timing receivers, but NOT ALL.

>> In other words, it has nothing to do with the receiver, it's
>> about what you ask it to do.
>
> because
>
> a) I never saw a navigation receiver featuring a "position hold" mode

Have you seen a DGPS-base station receiver? They are also in "position
hold" mode, even if its for a slightly different purpose. DGPS base
functionality is always (anyone with a counter example? ;-) ) an expensive
software option for a normal "navigation" GPS receiver.

> b) I never saw a timing receiver featuring a "navigate forever" mode.
> Everything that i had in my hands had a "automatic site survey" mode
> after which it would return to "position hold". That's why i think the
> formulation that it depends on the receiver's primary purpose is not
> that wrong!

Motorolas, now ancient, Oncore VP was used as timing receiver, it could do
DGPS corrections -- in a motorola specific format, it could also run in a
normal navigation mode. Ofcause this is not at the same instant in time!

To get a good timing receiver we want a 1PPS with low jitter. That is most
probably not a priority for high volume non-timing GPS receivers. But
besides the 1PPS-hardware limitations, I do not see why a good navigation
receiver, could do good in timing applications.

--

   Björn