[time-nuts] Does GPS time reception work everywhere all of the time?

[Magnus Danielson]

On 08/29/2010 01:31 AM, Bill Hawkins wrote:
> I'm involved with time synchronization of control system
> computers for multi-national businesses. GPS springs to
> mind as a way to synchronize time anywhere. Or is it?
> What about monsoon rains?
>
> The Internet is available almost everywhere that control
> computers are used, but many users prefer to use a data
> diode between them and the Internet. Control computers
> are now essential for manufacturing processes. Some of
> the processes run constantly for years without stopping
> for any kind of security update. Some of the downtimes
> cost millions of dollars per day.
>
> A GPS time system allows the control systems to be
> synchronized in time, so that messages sent periodically
> through the data diodes will have the correct time stamp
> on various events that occur in the process.
>
> But does that work everywhere all of the time? Where can
> I find answers?
>
> Thanks in advance, as we used to say.

The simple answer is either:

Yes.

or

No.

Never expect it to just "be there", it won’t be and you will be unhappy 
about it. The reasons for it can be many, but most of them involve 
single point of failure aspects.

If you handle those properly and mitigate equipment failures, cable 
failures, antenna failures, extreme weather conditions, power failures 
etc. you would for most practical uses be able to assume the existence 
of a signal... but then again... additional external effects like 
intentional or unintentional jamming comes into it.

So, redundant antennas and receivers, and add hold-over properties and 
surveillance of signal properties...  keeping an eye on things at all 
times, then you approach some degree of perfection of a local site.

Geographical redundancy may help further.

Cheers,
Magnus