[time-nuts] GPS interference and history...
James C Cotton
jim.cotton at wmich.edu
Sun Jun 12 01:43:36 UTC 2011
Any enterprise large enough to have an IT deparment needs
precise timing. The cheapest stratum one source is GPS.
I work at a Research II university and have several in our network.
The time is the public key for our routers that send encrypted
routing table updates to each other.
There are several "mushrooms" over the EE wing of the College of
Engineering, and at least one over the ME neighborhood for some
laser measurement equipment...
One EE lab that is doing some GPS signal analysis has at least one
16 way splitter...
----- Original Message -----
> From: "Jim Lux" <jimlux at earthlink.net>
> To: time-nuts at febo.com
> Sent: Saturday, June 11, 2011 10:08:18 AM
> Subject: Re: [time-nuts] GPS interference and history...
> On 6/10/11 7:01 PM, Hal Murray wrote:
> > lists at 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 timing antennas are sprouting like mushrooms in a lawn all over
> (that's what they look like... you'll be walking around, and you'll
> notice that there's 2 or 3 new stalks sticking up with a little
> on the top, and conduit running down the side of the building)
> While we have masers and cesium sources at JPL, they're not
> everywhere. So, usually, the "easy" solution is to just get yourself a
> Symmetricom or Fluke box, have facilities install the antenna, and
> lab is set.
> > 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.)
> > 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.
> GPS is easy, that's why. It's under YOUR control. You spend a few
> thousand bucks (including installation labor) and you have something
> that works now and for the foreseeable future that you don't have to
> worry about a comm line dropping, or resetting a clock or any of a
> multitude of things.
> Think about it.. what other totally off the shelf approach is there to
> get time to 1 second accuracy over a span of years and temperatures
> does not require periodic "setting the clock"
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