[time-nuts] Iridium source?

Bob Bownes bownes at gmail.com
Tue Oct 6 22:32:32 EDT 2015


You say GPS isn't available 'often'. Can you define 'often'? As in not at
some locations, or as in GPS signal is only available now and then

If the latter, any GPS timing unit with decent holdover should solve the
issue. If the former, well, you've gotten some replies on that.

Failing that, what are your drift tolerances? If you can manually set the
time, or get it 'close' with ntp & friends, a rubidium standard may jitter
a bit, but is pretty stable long term, even if you loose the NTP feed.
Cesium might drift a bit more...


btw: Welcome to time-nuts. These folks are our kinda crazy.

On Mon, Oct 5, 2015 at 4:24 PM, John Todd <jtodd at pch.net> wrote:

> I’m working on a project that needs a good clocking source deep inside of
> noisy environments (data centers and the like.)  This can’t be
> network-based - it needs to be independent of the systems surrounding it,
> and GPS/GPS-like systems will often be unreachable.  I’ve read up a bit on
> Iridium - it appears that there is some mention of Boeing saying (see slide
> three in below link) that the Iridium LEO network can be used not just as a
> GPS assist, but as an actual timing source.  Their frequencies on the
> timing side seem to penetrate buildings better.  Before you say “Iridium
> doesn’t work indoors!”, this may not be the case with their timing signals.
> Has anyone actually used this method for obtaining high-precision time?
> If so, is it possible to do with something smaller/cheaper than the full
> Iridium chipset?  I think the Iridium Core 9523 is something like $1300,
> which puts it outside of consideration for the large deployment we’re
> looking at doing, and we don’t need the voice/data TX or RX components.
> https://transition.fcc.gov/bureaus/pshs/docs/summits/911%20Location%20Acuracy/Barry_Martin.pdf
> Apologies if this is not on-topic here or if there are obvious data that
> I’m missing - I’m a bit new to this niche of the world.  I can’t find any
> mention of this topic past 2012, and it’s sparse even at that.
> JT
> ---
> John Todd - Senior Technologist - jtodd at pch.net - +1-415-831-3123
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