Atomic Clock Radio and GPS

[+geospotter]

We've all seen those clocks that set themselves to an atomic clock in Colorado (haven't you?).

 

I never bought one because I figured it probably wouldn't receive a signal from Colorado here in New England.

 

I began to suspect that maybe the radio received its time info from the atomic clocks on GPS satellites. Seemed like a good idea.

 

So, I went here to find out.

 

Looks like I was wrong on both counts.

 

The last paragraph is interesting.

 

geospotter

[+Gloom]

quote:

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The only thing more accurate that you can carry around easily is a GPS receiver, which derives atomic clock accuracy in real time from the atomic clocks in orbiting GPS satellites.

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So how come I still have to enter the time into my GPS and it doesn't correct for daylight savings?

 

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Duct tape is like the Force. It has a light side and a dark side, and it holds the universe together.

[Kerry.]

The GPS system certainly has that capability, which is what the "T" (Timing) stands for in NAVSTAR. However not all GPS receivers (as such) are designed to handle exact timing functions apart from what is used in range determination.

 

The "Time" as displayed on most handheld type (and similar types) receivers is "close" but not exact as this time display function is of low importance in regards to processor priority.

 

As a result of processor priority the displayed time can be about 0.5 seconds and up to 2 seconds out (and generally behind).

 

Specific receivers that handle time functions are a little different to navigation typr receivers.

 

As for daylight saving that's a people thing and in reality GPS time is different to UTC time from which time zones are applied and then silly DST on top of that.

 

GPS time and UTC time are different (currently 13 seconds) as the earth is gradually slowing down.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

 

[This message was edited by Kerry on January 23, 2003 at 02:57 PM.]

[+Cachetrotters]

If I'm not mistaken, leap seconds are not added to the GPS clocks. When the Earth Rotation Service adds leap seconds, only the UTC system earthside gets it. Receiver software takes care of the mismatch, yes? If a leap second were added this year(but it looks like it won't be), then would we get a new software release for just that?

 

As for receiver time setting, I only had to tell the GPSr what the hour was. Not minutes/secs.

 

don

[+EraSeek]

''Some have wondered how accurate the time display is on Garmin GPS receivers such as G-12XL, G-II+, and the G-III. Here is an answer provided by Garmin Engineering. This also explains why the GPS can be locked for awhile and still differ from UTC by 11 or 12 seconds. (This answer applies to other brands of GPS receivers as well.)

Start of Garmin quote>

 

Provided the unit has collected current leap second count from the navigation message, (current leap second difference from GPS time is only broadcast once in a 12.5 minute Nav. message), or current leap second has not changed since the last time the unit collected this variable, the time displayed on the front of the unit should be accurate to within 1 second of UTC.

 

>end of Garmin Quote

 

Joe Mehaffey comments:

This means that IF your GPS does not have (or does not save) the leap second offset from last time it was operated, your time may be off by perhaps 12 seconds until the complete NAV MESSAGE is received by the GPS. Jack and I have observed that "typically" Garmin GPS receivers display time which is delayed from about 1/2 to 1 second behind UTC. Lowrance GPS receivers are usually between 1 and 2 seconds delayed behind UTC. In both cases, this is a result of the display driver subroutine having low priority as the "GPS internal clock" is within a few nanoseconds of correct.

 

Similarly, the NMEA time output on the serial link is typically delayed a second or two depending on various factors.

 

Joe Mehaffey ''

 

[+Cachetrotters]

So in effect the receiver does take care of it, through the nav message, but not as a direct result of software knowing how many to add(written into the code, etc.). Just knows to add what's in the message.

 

don

[+EraSeek]

This may also be of interest:

Primary Atomic Reference Clock in Space

 

[+GEO*Trailblazer 1]

Is approximately 100 feet depending on the Circumference of the circle.The minutue is a unit used to measure both time and angles.In time,60 minutes = 1 hour.Each minute is divided into 60 seconds.Because an hour is 1/24 of a day,a minute is 1/14,440 of a day.In measuring angles,60 minutes make up 1 degree.A circle is divided into 360 degrees,so one minute is 1/21,600 of a complete circle.Each minute of an angle is divided into 60 seconds.The minute in time is an exact measurement,which means exactly so much time.The minute of an angle is an exact portion of a circle.But if the angle is denoted by a linear measure along the circumference of the circle,the distance of the minute depends on the diameter of the circle.On the Surface of the Earth it is one NAUTICAL MILE, about 6,076 feet(see Mile). The World Book Encyclopedia. This is what was used Called the GREENWICH HOUR 0,Now I believe the Satellites use the CS= Cesium, RB=rubidium, Clock.And another Clock will post link. www.navcen.uscg.gov Go to GPS Get daily updates of the Operating satellites.

 

When all else fails Geotry again.

 

[This message was edited by Trailblazer # 1 on January 23, 2003 at 08:53 PM.]

[Cholo]

All the talk about extreme accuracy in time and location calculations is hooey. Who can really prove any of this? We tend to believe alot of long drawn out explanations, but belief is just that, belief. When did time start? Where is W022.9823079 degrees x N5.1531416 degrees? Maybe some geogeek will go there and take a photo of his geogadget with all those numbers on it. There ya go, that's proof! It's all relative, and something to talk about, just like the weather.

[+apersson850]

Recent studies have shown that there is no place at all at exactly W022.9823079 degrees x N5.1531416 degrees.

Did you know that, or how come that you typed in exactly that place that doesn't exist????

 

Anders

[Kerry.]

quote:

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Originally posted by Cholo:

When did time start?

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Time, which time (GPS time) precisely midnight on the 5/6 january 1980 and hasn't changed since

 

quote:

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Where is W022.9823079 degrees x N5.1531416 degrees?

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What Datum and specific ITRF would you like that in

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+bradtal]

My wife and I always laugh at this. We live less than a mile from the antennas that broadcast the atomic time code.

 

However, every single clock in our house is different, and none of them show the right time.

 

 

I do use my GPSr to set the clocks when power goes out, etc.

 

Brad

 

Hard work pays off in the future, laziness pays off now.

[+GEO*Trailblazer 1]

I guess thats why they call surveying an art it is theory and the practice of it.If at one time,you start at Greenwich Hour 0,which was the accepted practice until the GPS,And now we are using a diffrent set of clocks,would this then change the aspect of a point,its longitude and lattitude?In my opinion yes,this is what all the correction is about.Because originally they used a compass and a sextant to navigate.These changes constitute a large error,which is stated in the survey books,we always begin with an error!As far as precise measurements,"the GPSr is .004ths of a percent in the center of the bulls eye,Space Shuttle Commander Kevin Kreigel"on a laser shot taken Feb. 14 2001 from the Space Shuttle at an asteroid,The mission to remap the Earth.So then What is the defaniton of precise? Precise to what standard?I believe this is why we are all working to get the data sets together so we have a (Defined Control),with a data base.As we can all see it will take alot of time and money to get what should have been done to begin with.

 

When all else fails Geotry again.

[Lyra]

quote:

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Originally posted by bradtal:

My wife and I always laugh at this. We live less than a mile from the antennas that broadcast the atomic time code.

 

However, every single clock in our house is different, and none of them show the right time.

 

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That's pretty funny! A few years ago, I was in one of those nature gizmo stores that have made their way into lots of malls (The Nature Company? I'm drawing a blank on what they're called) and they had this big bin of cheapo keychain compasses. As I looked at them, something struck me as unusual, and then it dawned on me what it was. No two were pointing in the same direction.

 

Always wear proper caching safety equipment!

[+Team GPSaxophone]

quote:

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Originally posted by bradtal:

My wife and I always laugh at this. We live less than a mile from the antennas that broadcast the atomic time code.

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But you live on Fort Collins. I thought the atomic clock was in Boulder.

[Cholo]

quote:

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Originally posted by Anders:

Recent studies have shown that there is no place at all at exactly W022.9823079 degrees x N5.1531416 degrees.

Did you know that, or how come that you typed in exactly that place that doesn't exist????

 

Anders

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To quote Johnny Carson: "I did not know that."

To quote me: "It seemed like it might be a much warmer place than here."

As to your question, "how come?", that's what the Indian chief asked when they tied his......uh, never mind, that's too far off topic.

[+rdw]

quote:

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Originally posted by Team GPSaxophone:

 

But you live on Fort Collins. I thought the atomic clock was in Boulder.

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WWV and WWVB both broadcast from Fort Collins. The website has the coordinates for the antennas.

 

rdw

[+bradtal]

quote:

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But you live on Fort Collins. I thought the atomic clock was in Boulder.

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I think the "headquarters" are in Boulder, but the antennas are in Wellington. I think it's interesting that they say they are in Fort Collins, because they really aren't. They are a few miles north of Fort Collins, in Wellington.

 

Check out this picture to see what the antennas look like. These things are huge! The pictures don't do them justice. My house is near the houses in the background of the picture.

 

Check out this picture to see a satellite image of the area. The building in the middle houses all the machinery, and you can see the antennas (and their shadows!) surrounding the building.

 

Another funny thing about these antennas... My neighbor plays the electric guitar, and he actually picks up the signal from the antennas though his guitar and amp. I've been over there and he sits there and listens to the tones/beeps/announcements, etc. Told him his amp is the most expensive atomic clock I've seen.

 

Hard work pays off in the future, laziness pays off now.