WASS no working?

[+EraSeek]

quote:

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Originally posted by Kerry:

 

Similar with displayed time, a recreational GPS receiver doesn't give much priority (really at all) to worrying what the time is, if it's a few seconds out nobody really cares.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

---

 

Now, yes, the display for time on the GPS is not all that accurate by itself, but I recall reading that because the almanac is updated (what is it) every 12 mins, it also adjusts the display's time, there by keeping it very accurate! Am I wrong here?

 

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

[+apersson850]

I think you aren't using the same benchmarks when it comes to judging accuracy. While it's true that timing is critical to a few nanoseconds for the positioning to be done correctly, a recreational receiver doesn't care about if the displayed time is a second or two off.

When I do some manouvers with my Vista, I can see that the clock display will simply be put on hold long enough to skip one second completely.

Still, it's a good enough reference for setting your watch, if that's what you want to use it for.

 

Anders

[Kerry.]

EraSeek, for sure the displayed receiver time is corrected via satellite broadcast messages but as Anders mentioned once the receiver gets bogged down doing some real work, stuff like the time display update is probably dropped from the list of immediate important things to do and gets a little behind, always behind never in front.

 

Still by far the best timing device there is, leap seconds and all.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Marsha and Silent Bob]

quote:

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Originally posted by Kerry:

An external antenna in most cases would make one hell of a difference to reliable WAAS reception, assuming suitable reception and of course not everybody does get suitable signal reception.

---

 

Well of course it would, but it was also make them very large devices and not suited for most people's purposes (inside the car, most geocaching, etc). There are of course people that prefer external antennas, but most would prefer the unit be pocket sized.

 

quote:

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Really the recreational side of WAAS software doesn't take into account the full capabilities of WAAS and it wasn't all that long ago that receivers marketed as supposedly 1 second position updates, simply couldn't achieve that claim either.

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Of course it doesn't. That's why the units are labeled "recreational". That doesn't mean that it doesn't handle WAAS. Like I said, I am usually WAAS locked (even under heavy tree cover) and accurate to about 20ft. That's with a "low CPU powered" internal antenna Vista.

 

quote:

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That simply points to lack of processor power (or basically priority being directed to the primary purpose of a GPS receiver, position, position, position) in many cases but things are getting bigger and better but at a cost and cost is what most manufacturers have to keep down.

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*MOST* people aren't using their GPSs for Geocaching OR WAAS (or even care what WAAS is). The reception on these receivers is good enough for what they were intended for.

 

quote:

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Similar with displayed time, a recreational GPS receiver doesn't give much priority (really at all) to worrying what the time is, if it's a few seconds out nobody really cares.

---

 

That's because a GPS receiver is just that. It's not an atomic clock, nor is it an atomic clock radio receiver

 

Just my worthless .02

 

[+apersson850]

quote:

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Originally posted by Marsha and Silent Bob:

That's because a GPS receiver is just that. It's not an atomic clock, nor is it an atomic clock radio receiver

---

Well, actually it is, in a way.

The GPS itself has a quartz controlled oscillator, like an ordinary wristwatch. It's a little better than that, since there is a temperature compensation mechanism as well, but anyway.

However, when the GPS is doing its particular trick, calculating the position, it must also calculate the time to a high accuracy. To get a feeling for what's required, one nanosecond is equivalent to 0.3 meters, or one foot, if you are kinky.

The time that's calculated in the receiver is based on the time that's transmitted from the satellites, and they do have an atomic clock on-board. Actually, as far as I know they have three, which are corrected against each other. They are also corrected against even more accurate such clocks on the ground. So one could say that you have a virtual atomic clock in your GPS. Reasonably, its even better than the normal, radio-controlled clocks, since it receives information from more than one transmitter, and can thus average out possible errors and/or noise.

What I and Kerry pointed out above, is that the display of current time on the GPS screen isn't a main task of the unit, so even if it inside knows very well, the time displayed to the outside world may lag a little, depending upon the workload on the processor inside the unit.

 

Anders

[+Marsha and Silent Bob]

quote:

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Originally posted by Anders.:

What I and Kerry pointed out above, is that the display of current time on the GPS screen isn't a main task of the unit, so even if it inside knows very well, the time displayed to the outside world may lag a little, depending upon the workload on the processor inside the unit.

---

 

What I am saying is that this is irrelevant (from what I understand of the thread). Who cares if the CPU can't handle the time output to the screen? It's not a vital function.

 

The CPU power in the units is high enough to do WAAS without an issue.

 

[+apersson850]

Well, it's up to you if it's relevant to you or not. It was you who stated that it doesn't work like an atomic clock radio receiver. I think one can say that it does just about the same job as such a receiver. In that regard your post was wrong. People reading erroneous posts will be mislead, unless someone corrects them. Please disregard my effort to shed some light on the subject, in case you want to stay in the dusk.

 

Anders

[+Marsha and Silent Bob]

quote:

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Originally posted by Anders.:

I think one can say that it does just about the same job as such a receiver. In that regard your post was wrong. People reading erroneous posts will be mislead, unless someone corrects them. Please disregard my effort to shed some light on the subject, in case you want to stay in the dusk.

---

 

While this is getting slightly OT, I would like to clarify my statement to end your apparent confusion...

 

The GPS unit's main function is not that of an atomic clock radio receiver. It's main function is not to display the accurate time on the screen.

 

I hope that clear it up for you.

 

[Kerry.]

Getting a little mixed up here, I think.

 

Really what the user prefers is not equiv to what a person might require. Sure if a person wants a compact internal antenna model then that's what THEY want but if that configuration doesn't do the job then that's their problem. They either accept that or look for ways/methods to improve things.

 

As for many of the other comments Bob it's probably safe to say a similar approach applies. Like the "which is the best GPS" query, no specific answer without specific details. Much like "dense tree cover", what is dense tree cover to you might not be dense tree cover to me.

 

As for time, nobody is making an issue out of time apart from the fact that some receivers do a lot better at doing things than others but then it depends on many other things. What is relevent to some is not necessarily relevent to others but myths need to be corrected before they become fact as they have in the past.

 

What some see as just a GPS unit that gives position is not the only function of the system remebering that NAVSTAR does stand for NAVigation Satellite Timing And Ranging and many forget the important Timing and Ranging functions that GPS actually provides other users.

 

As for WAAS having enough processing power I doubt if WAAS could ever have enough processing power. Sure it might be enough but if WAAS was as stable as some claim then there wouldn't be so many questions about why it doesn't work for them.

 

Really WAAS has been blown out of proportion and WAAS actually took a hit when SA was discontinued. Is the improvment in accuracy worth the 6 thousand million dollars it has cost, so far.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

 

[This message was edited by Kerry on September 04, 2003 at 06:44 PM.]

[+EraSeek]

I discuss these things because I like to learn and give to the discussion what I know. Mostly learn.

 

That being said, you said: "The GPS unit's main function is not that of an atomic clock radio receiver". Well not exactly. Quite frankly that is what it is, or the base of what it is. All depends on acurate timing! It has to be a lovely atomic time reciever or it is junk. Useless.

 

On the topic of radio atomic clock recievers:

 

"Once your radio-controlled clock has synchronized, it won’t decode the signal from WWVB again for a while. Some clocks only decode the signal once per day, others do it more often (like every 4 hours or every 6 hours). Those that decode the signal just once per day usually do it at night, since the signal from WWVB is much stronger once the sun goes down. In between synchronizations, the clocks keep time using their quartz crystal oscillators. A typical quartz crystal found in a radio-controlled clock can probably keep time to within 1 second for a few days or longer. Therefore, you shouldn’t notice any error when you look at your clock display, since it will appear to be on the right second, even though it has probably gained or lost a fraction of a second since the last synchronization."

 

Every day, or 4 to 6 hours? You GPS display updates more often than that.

 

The GPS system is often refered to as the worlds premier time transfer system! Exceding the radio broadcast system of atomic time. I'll see if I can find my references to it again.

 

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington

[Kerry.]

EraSeek, interested in the time side of things, then the following is a cell phone tower site. That cone shaped looking thing is a fixed GPS antenna connected inside to basically a GPS receiver. Doesn't go anywhere, doesn't move, just tells the time and keeps the network in sync.

 

everybody keeps telling me where to go

[+EraSeek]

CooL!

Yes I am interested in the time side of things.

HERE is a link to the world's first World's Clock. Coming soon.

[+EraSeek]

Here is how many atomic clocks they have on board:

"SATELLITE CLOCKS

================

Each Block II/IIA satellite contains two Cesium (Cs) and two Rubidium

(Rb) atomic clocks. Each Block IIR satellite contains three Rb atomic

clocks."

[Kerry.]

And it's basically the advanced Rubidium's on the Block IIR's (and IIR-M's) that have given improved performance in timing and position.

 

We just need more of them but many of the existing Block II's/IIA's simply won't die quick enough. The Rb's on the II/IIA's are basically 15 year old technology and the more IIR's with the new Rb time standards we get the better.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+EraSeek]

Just wait till they get a Mercury Ion clock to put on those babys! The Atomic clock has an error of 1 sec in 6 million years. And the upcoming Mercury ion clock will have an error rate of 2 seconds since the beginning of time itself.

[Kerry.]

EraSeek, have a little look at this lot then (in your spare "time")

 

Time Lords

 

Becoming very serious stuff, seriously.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Marsha and Silent Bob]

quote:

---

Originally posted by EraSeek:

That being said, you said: "The GPS unit's main function is not that of an atomic clock radio receiver". Well not exactly. Quite frankly that is what it is, or the base of what it is. All depends on acurate timing! It has to be a lovely atomic time reciever or it is junk. Useless.

---

Again, I believe the point of the post was that it didn't have the CPU power to put the exact time (from the atomic clocks on board the GPS sats) on the screen of the GPS units.

 

Thus, while it needs to receive the exact time for doing its precise calculations, it's sole function is not that of an atomic clock radio receiver (thus does not have a lack of CPU power which was the original point).

 

It has the CPU power to use the time just not output it as frequently as it is updated internally.

 

Silent Bob

 

[+EraSeek]

Yes, I understand. The point being that sometimes the unit's processing gets in the way of the display functions. If you Leave WAAS off, and maybe turn off maps, I'll bet the GPS display would still beat an atomic wristwatch hands down.

 

I wa just making the point for discussion that the most important process of a GPS is as an (internal) atomic time reciever.

[+EraSeek]

quote:

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Originally posted by Kerry:

EraSeek, have a little look at this lot then (in your spare "time")

 

http://www.ucolick.org/~sla/leapsecs/onlinebib.html

 

Becoming very serious stuff, seriously.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

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Looks intereseting. I'll read more after work...

[+EraSeek]

"This table shows that although leap seconds in UTC will become more and more frequent, the current scheme for UTC will almost certainly work for the next 1200 years. This gives plenty of time to develop a solution which satisfies the systems that need atomic time as well as civilizations that are accustomed to mean solar time"

 

In the mean time, maybe you can get these guys to convience the US to go metric! Now there would be a usfull change!

 

As for my previous post: "If you Leave WAAS off, and maybe turn off maps, I'll bet the GPS display would still beat an atomic wristwatch hands down." Yes, I know that was a frivilous(sp?) aguement. Niether display would be refined enough to judge. I just like my GPS.

[+st_richardson]

quote:

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Originally posted by EraSeek:

Just wait till they get a Mercury Ion clock to put on those babys! The Atomic clock has an error of 1 sec in 6 million years. And the upcoming Mercury ion clock will have an error rate of 2 seconds since the beginning of time itself.

---

 

Can I get one for my wrist?

[+EraSeek]

Well, as a mater of fact.. they are nearly there! How about 7cm's. Check this out: http://www.bldrdoc.gov/timefreq/ofm/smallclock/index.htm

 

 

"See the wonderous works of Providence! The uncertainty of human things!" Geo.Washington