Any large IT organization has multiple "stratum 1" GPS based
timing receivers.
The public key for our internal routing updates is the time. No time and
the routing would break. We route ~10+ Tb/hr in the 8am-5pm business
day. That would be noticed by our users...
On one building on our campus (College of Engineering ~1/4 mile long
building )
I counted 14 mushroom antennas, I see other patch antennas on windows...
Jim Cotton
On 1/13/12 9:29 AM, Jim Lux wrote:
On 6/10/11 7:01 PM, Hal Murray wrote:
li...@rtty.us said:
There's an enormous amount of gear out there that gets timing off of
GPS.
That's an interesting claim. Does anybody have any data on the usage
of GPS
for timing?
I assume there is one in every cell tower and one in every 911 call
center.
Are there other large categories of users?
GPS is pretty ubiquitous as a time source for data loggers in the
field, things like traffic signals, etc. There's real value in an
inexpensive little box that makes sure you don't have to set the
clock, even if the clock accuracy requirement is something like 1 minute.
What would it cost to replace all of it? If you wanted to do
something like
that, what would "it" cover? How about people like us running old
recycled
gear? (Z3801A, ThunderBolt, ...)
A fortune, quite literally
I think I saw one last week. It was on a river level measuring
station on
the Sacramento River. It was a small block building. There was an
antenna
pointing up into the sky. I assume there is a satellite up there.
There was
also a small (~3 inch dia) hemisphere antenna. I assume it was GPS.
(They
had power going into the building (no solar panels) so it should have
been
simple to get a phone line too.)
Not necessarily. And it's not cheap. Don't forget that you can't run
power and phone in the same conduit, cable, etc. So basically you're
doubling the physical plant installation costs to bring in phone, just
for the labor to bring it from the nearest point of presence.
Especially in rural farm kinds of areas, power is more pervaisve than
phone (gotta run irrigation pumps, etc.)
Adding a $100-200 GPS receiver (we're not talking GPSDO with OCXO
here..) is probably cheaper than running ANY length of phone wires:
just for the termination costs.
I suppose one could use some sort of GPRS cellular service and get
time, but then you're on the hook for a monthly subscription fee, etc.
cheap L1 only GPS is a great solution. Apply power, wait, you've got
accurate time. No need to have someone visit periodically and check
to see if the clock needs to be reset, etc.
I'm not sure why they need GPS at the recording house. They know
where it is
so timing is the only use I can think of. But they could also get
that at
the receiving end. Millisecond accuracy isn't helpful. Second level
accuracy might be interesting if something breaks and you want to
know when
the wave got to downstream stations. The risetime is probably over a
second.
You're right, they don't need milliseconds, nor do they need seconds,
probably.
There's really no other convenient way to get time to the nearest
minute that is as reliable and cheap as GPS. Think about it... WWVB?
WWV? Vertical pointing sun sensor?
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