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Improvements In Gps Accuracy


Kirbert
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An article in the May 2004 issue of Scientific American magazine describes in great detail how the GPS system works and how, starting in 2005, improvements will be made to the system (new satellites) that will:

 

a) provide a signal under tree cover and even indoors

B) improve the accuracy to +/- 30-50 cm, about 1-1/2 feet.

 

"Oh, goody!" I hear you say. But I think perhaps it'd be a good idea if we discuss the implications this will have on our game. It's one thing when the GPSr tells you you're within 30 feet or so of a cache; it'll be quite another when it tells you you're within 2 feet. I suspect most of the challenge would go away. And if that happens, the popularity might fall off.

 

If we decided to do something about that -- either when faced with the changes or now in anticipation of the GPS improvements -- there are a couple of ways we could go:

 

* We could just let it happen, and let the game evolve into a new form based on the improved accuracy.

 

* We could establish a few policies that would keep the game much as it is now.

 

* We could do BOTH -- diverge into two types of geocaching, one "old school" where some thinking and some searching is involved, and a new game where the GPS takes you right to the desired waypoint.

 

For keeping the game as is, here are a couple of ideas:

 

1) Coord listings could be limited to three decimal points. With the improved GPS accuracy, it will probably become common to provide four or five decimal points.

 

2) Placers could be advised not to provide the EXACT coords for a cache, but rather a location NEAR the cache, and the listing could say "cache is within 30 feet of location given."

 

In any case, we'll probably need to address the changes coming. Probably within a year or two, newbies will be hitting the trails with GPSr's that are MUCH better than the ones we are using, and we'll be getting reports about how easy some caches are and how the coords are all wrong on others.

Edited by Kirbert
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I think it's way too early to be concerned about this. For one thing, even if all the new sat's were in place and fully operational today, our current receivers would not get the accuracy of 1.5' that you quote. Our receivers need the L2 and the new L5 frequencies to improve accuracy to 1 to 5 meters. We might see a slight accuracy improvement due to stronger signal strength and therefore better satellite geometry under tree cover. You'll still need differential corrections to get from 1/2 to 5 meters accuracy and survey grade instruments to get to that 1.5' radius. Multi-freq receivers will be expensive and battery hogs. Let's see how things are in about 2 years. Probably not much different than today as far as geocaching goes. :huh:

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"Oh, goody!" I hear you say. But I think perhaps it'd be a good idea if we discuss the implications this will have on our game. It's one thing when the GPSr tells you you're within 30 feet or so of a cache; it'll be quite another when it tells you you're within 2 feet. I suspect most of the challenge would go away. And if that happens, the popularity might fall off.

 

Not true.

 

Even the accuracy improves, half the treasure is the hunt, and the other half is the find. Geocaching will still take me to areas that are scenic and enjoyable.

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"Oh, goody!" I hear you say. But I think perhaps it'd be a good idea if we discuss the implications this will have on our game. It's one thing when the GPSr tells you you're within 30 feet or so of a cache; it'll be quite another when it tells you you're within 2 feet. I suspect most of the challenge would go away. And if that happens, the popularity might fall off.

 

Not true.

 

Even the accuracy improves, half the treasure is the hunt, and the other half is the find. Geocaching will still take me to areas that are scenic and enjoyable.

BINGO. Technical issues aside, this is THE reason I geocache. To see places I have never seen or noticed. Just about right next door, too!

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Yeah if they managed to increase GPSr accuracy so it would get me to within a foot of the cachesite "at least most of the time", that'd reduce my enthusiasm for the sport. I don't think it would stop me from participating, but it'd make things a bit *too* easy.

 

Already I'm hearing more & more people claim autorouting is a "vital tool" of a Geocaching GPS, but to me you might as well take a taxi to the cache site. Hey in future you'll be able to tell your car's onboard navigation system where the cache site (or nearest parking spot) is and it will auto-drive the car for you.

 

..then from there your GPSr will take you to within 1-2 feet of the cache? :huh:

 

And, how the heck are they gonna make a GPSr work "indoors?" :huh:

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half the treasure is the hunt, and the other half is the find. Geocaching will still take me to areas that are scenic and enjoyable.

Exactly, I get more pleasure from the 3 mile walk than I do from the opening of the box....

 

Depending on the location my GPS has put me within a metre or two, still have to rummage around though - plus you're never sure if it is accurate until you've found the cache.

 

As for indoors, I can get at least 1 satelite in most rooms of my house - big windows!! I assume they'll be increasing the sensitivity of the units rather than boosting the output.

 

Are we going to stop using mapping software as that makes it easy?? At the end of the day you can play the game however you like, whether you want to use a map & compass , a basic GPS or an all singing mapping unit......

 

Chalky

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I assume you are talking about this article. It is only partial article and I havn't read the entire thing because I don't have a subscription.

 

Scientific America also published this article a year eirlier.

 

According to the 2003 article the first GPS III satalite won't be ready for deployment until 2010. Any major change in the GPS constellation, I assume, would require at least a firmware upgrade. And any addition of frequencies would require you to purchase a new GPSr to take advantage of the new frequencies.

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1) Coord listings could be limited to three decimal points. With the improved GPS accuracy, it will probably become common to provide four or five decimal points.

 

you better check but you can only now list a waypoint to three decimal points for decimal minutes.

 

Anyway I imagine it will still be hard enough, LOL.

 

cheers

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I think it's way too early to be concerned about this. For one thing, even if all the new sat's were in place and fully operational today, our current receivers would not get the accuracy of 1.5' that you quote. Our receivers need the L2 and the new L5 frequencies to improve accuracy to 1 to 5 meters. We might see a slight accuracy improvement due to stronger signal strength and therefore better satellite geometry under tree cover. You'll still need differential corrections to get from 1/2 to 5 meters accuracy and survey grade instruments to get to that 1.5' radius. Multi-freq receivers will be expensive and battery hogs. Let's see how things are in about 2 years. Probably not much different than today as far as geocaching goes. :huh:

Additional satalites will not imporve accuracy. The new satalites (GPS III) will be replacing the old satalites (GPS II) as they age and are decomissioned (become a shooting star).

 

Boosting the power of the satalites will only help us overcome loosing satalites under tree cover and inside buildings. It would have very little effect on accuracy. You still have to contend with the ionosphere.

 

The biggest improvment in accuracy will be the introduction of dual and multi frequency GPSrs. The ionosphere affects frequencies differently and corrections can be made by your own GPSr. It is simular to (but the same as) having your own personal portable WAAS station.

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Bushwhacked Glenn Posted on Feb 21 2005, 12:13 PM

Boosting the power of the satalites will only help us overcome loosing satalites under tree cover and inside buildings. It would have very little effect on accuracy

 

The single most significant factor affecting accuracy is satellite geometry. Boosting signal strength will get us better coverage under tree cover and therefore better satellite geometry. That means better accuracy under the right conditions.

 

There are no block III satellites. The new satellites to be launched this year are block IIR-M sat's. They will have a new signal added (L2C on the L2 frequency) which will give an accuracy of 5 to 10 meters for those receivers that can receive the L1 and L2 freq's. The fourth generation of satellites (block IIF) are scheduled for launch beginning in 2006. These will include the new L5 signal and provide accuracies of 1 to 5 meters for the multi-freq receivers.

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There are no block III satellites. The new satellites to be launched this year are block IIR-M sat's. They will have a new signal added (L2C on the L2 frequency) which will give an accuracy of 5 to 10 meters for those receivers that can receive the L1 and L2 freq's. The fourth generation of satellites (block IIF) are scheduled for launch beginning in 2006. These will include the new L5 signal and provide accuracies of 1 to 5 meters for the multi-freq receivers.

Do you know what the Scientific America articles that I liked to are refering to when they say GPS II and GPS III?

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gps has not changed in years oh maybe by software improvements on the units and now color but accuracy with new gps satellites that's a big thing if it's coming out next year I will Waite

 

but if it's going to be the same system we have now for the next 3 years I will buy a the 60cs this year mayebe garmin will just give a firmware upgrade for the new satellites

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Correct me if I'm wrong, I thought the higher accuracy was already in place for the gov, but tempered for the average citizen.

 

What new thing do they need to open it to all? I thought it was policy, not technical.

If you're referring to the "selective availability" error that used to exist in consumer GPSr's, that was removed back in 2001(?)

 

Nowdays I believe our handheld units are just as accurate as military handheld units.. umm right? In fact I've heard army dudes often use civilian GPSr's while on duty because they're easier to operate than their own :)

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Correct me if I'm wrong, I thought the higher accuracy was already in place for the gov, but tempered for the average citizen.

 

What new thing do they need to open it to all? I thought it was policy, not technical.

The military receivers use an encrypted code transmitted on both the L1 and L2 frequencies. This allows them to quickly dither or turn off the "civilian" signals.

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IVxIV Posted: Feb 21 2005, 04:43 PM 

Nowdays I believe our handheld units are just as accurate as military handheld units.. umm right?

 

Not unless yours can receive both L1 and L2 signals. The ability to receive two different frequencies is what allows reduction of ionospheric errors which is the cause of the most error next to satellite geometry.

 

It does seem that the military uses a lot of "civilian" receivers. Iv'e even seen them on Navy ships.

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right from the D.O.D WEBSITE

 

The Boeing Co., Hunting Beach, Calif., is being awarded a $143,903,755 contract modification for the Navstar Global Positioning System Block IIF contract to provide the next generation for advanced GPS satellites with enhanced navigation support for both military and civilian users. This modification consists of exercising the option to begin production of Satellites (Space Vehicles) 07 through 09 and initial funding in calendar year 2005. Total funds have been obligated. This work will be complete June 2008. The Space and Missile Systems Center, Los Angeles Air Force Base, Calif., is the contracting activity (F04701-96-C-0025, P00332).

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Ok first I should say I'm new to all of this but have been using GPS now for some 8 years or so and I'm a fast learner. I worked for the military and had my own personal GPS V with me many times when I went out doing survey and other such things like recovering SCP's and benchmarks. When out int he open my GPS and the militarys were just about the same mine would be off no more then a few feet from a 24 hour AAA survey (even though I was never allowed to call it better then class 3 survey). When the masking occured my GPS held it's position alot better because the military ones had to deal with pdop and other things requiring the accuracy to be within specs like no more the .2 inches in any direction. As many have said the L1 and L2 recievers are the one that would give you the best accuracy but with mine or even the govt. GPS it was still hard enough to find a 1' tall monument with a mteal disk in it sitting there above the ground so I doubt any better accuracy will make finding the final item any easier. And as many before pointed out it's the thrill of the hunt not what you find that makes caching fun. I would hope imporved signal wouldn't make people lose intrest (especially since I doubt any of us use an alminac and get 100 hits when we place and mark a cache, and that's to the lowest possible survey standards). I hope nobody stops caching just because they can get within 1' of the cache because mine now can do that but it still takes me 20 min to find a cach sometimes depending on how well it was hidden.

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Bushwhacked Glenn Posted on Feb 21 2005, 12:13 PM

Boosting the power of the satalites will only help us overcome loosing satalites under tree cover and inside buildings. It would have very little effect on accuracy

 

The single most significant factor affecting accuracy is satellite geometry. Boosting signal strength will get us better coverage under tree cover and therefore better satellite geometry. That means better accuracy under the right conditions.

 

There are no block III satellites. The new satellites to be launched this year are block IIR-M sat's. They will have a new signal added (L2C on the L2 frequency) which will give an accuracy of 5 to 10 meters for those receivers that can receive the L1 and L2 freq's. The fourth generation of satellites (block IIF) are scheduled for launch beginning in 2006. These will include the new L5 signal and provide accuracies of 1 to 5 meters for the multi-freq receivers.

Satellite geometry may have been the most significant factor when the GPS program was young and there less satellites in ordit. But now there are enough satellites that coverage is not a factor. Now if you said receiver geometry I would have to agree 100%. As the receiver geometry changes (open field, forest, inside a house) so does accuracy. However, since we are relating this geocaching, receiver geometry shouldn't be a factor. One would hope that the cacher would be looking for the cache in the same area that is hidden.

 

Ionospheric delay is the most significant factor when it comes to geocaching. Before the L2 signal was made available ionospheric delay alone could cause as much as a 100 meter error. The L5 signal is going to be esentially the same as the L1 signal. However, it will be broadcast on a different frequency. This will help mitigate some error and will defently help out in places where the frequencies for the L1 or L2 signal is being jammed or used for some other purpose. Will the addition of the L5 signal make a difference in the USA where the L1 and L2 signals are not being jammed or are being used for something else? I'm sure the extra frequency diversity will help. By how much, I'm not sure.

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from what I see on the internet using google I don't see any big upgrade that will make gps better anytime soon

Europe is making there own system. I here it will be much more accurate then the one we have now

 

and for me geocaching is not for the box of toys but for the nice walk and hike and if gps gets better then when we place a cache walk 30 feet away and take your readings

 

thanks

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right from the D.O.D WEBSITE

 

The Boeing Co., Hunting Beach, Calif., is being awarded a $143,903,755 contract modification for the Navstar Global Positioning System Block IIF contract to provide the next generation for advanced GPS satellites with enhanced navigation support for both military and civilian users. This modification consists of exercising the option to begin production of Satellites (Space Vehicles) 07 through 09 and initial funding in calendar year 2005. Total funds have been obligated. This work will be complete June 2008. The Space and Missile Systems Center, Los Angeles Air Force Base, Calif., is the contracting activity (F04701-96-C-0025, P00332).

Gee, thanks for limiting the search to all .mil websites. There arn't many of those. :)

Can you give me a link. I'm really interested in reading more.

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IVxIV Posted: Feb 21 2005, 04:43 PM 

Nowdays I believe our handheld units are just as accurate as military handheld units.. umm right?

 

Not unless yours can receive both L1 and L2 signals. The ability to receive two different frequencies is what allows reduction of ionospheric errors which is the cause of the most error next to satellite geometry.

 

It does seem that the military uses a lot of "civilian" receivers. Iv'e even seen them on Navy ships.

Okay.

 

Do we think that high precision accuracy is being opened to civilians?

 

It just doesn't to jibe with the past policy.

Edited by BlueDeuce
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and do you think garmin would have came out this year with the new c320 and c330 and any other new products if there is a plan for new gps satellites coming out next year or this year right? I think this new update is at least 5 years down the road although they are owned by stock holders they may pull that crap on us :-)

sell us all the old stuff now and make more money on the new stuff next year

Edited by igsonline
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and do you think garmin would have came out this year with the new c320 and c330 and any other new products if there is a plan for new gps satellites coming out next year or this year right? I think this new update is at least 5 years down the road

I found a good article on GPS Modernization at the FAA website.

 

Here are some quotes from it on the timeline:

The first of these new signals will be a Coarse/Acquisition (C/A) code located at 1227.60 MHz (L2), and will be available for general use in non-safety critical applications. This will be available beginning with the initial GPS Block IIF satellite scheduled for launch in 2003.
The L5 signal will be available on additional WAAS GEOs scheduled for launch in 2004/2005.
The other signal, located at 1176.45 MHz (L5), will be available on GPS Block IIF satellites scheduled for launch beginning in 2005.
At the current GPS satellite replenishment rate, all three civil signals (L1-C/A, L2-C/A, and L5) will be available for initial operational capability by 2010, and for full operational capability by approximately 2013.
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IVxIV Posted: Feb 21 2005, 04:43 PM 

Nowdays I believe our handheld units are just as accurate as military handheld units.. umm right?

 

Not unless yours can receive both L1 and L2 signals. The ability to receive two different frequencies is what allows reduction of ionospheric errors which is the cause of the most error next to satellite geometry.

 

It does seem that the military uses a lot of "civilian" receivers. Iv'e even seen them on Navy ships.

Okay.

 

Do we think that high precision accuracy is being opened to civilians?

 

It just doesn't to jibe with the past policy.

I doubt "civilian" receivers will ever be used officially by the military for navigation. However I've seen "civilian" receivers used in military equipment that use the GPSr to get accurate timing.

Edited by Bushwhacked Glenn
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It's one thing when the GPSr tells you you're within 30 feet or so of a cache; it'll be quite another when it tells you you're within 2 feet.  I suspect most of the challenge would go away.  And if that happens, the popularity might fall off.

To me, "The journey is more important than the destination", but even if the destination is your main geoecaching interest, improved GPSr accuracy shouldn't ruin geocaching:

  • If you enjoy the challenge of finding the physical caches, turn your (more accruate) GPSr off when you're 30 feet away.
  • If you enjoy creating difficult hides, improve the location of your hides or your camoflage, or create multi- or puzzle caches.

Deliberately supplying inaccurate coordinates, as some have suggested, would be a lazy way to create more challenging hides, and would have the effect of increasing the wear and tear on the area as seekers turn over every stone in the wrong place! Somehow, I don't think saying "I created a really challenging hide by giving false coordinates" is going to earn much respect. :)

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I read the whole thread, and still, all I hear is blah blah blah blah blah.

 

I want to make some smart comment, but the only thing I understood out of all of that was the part glenn posted. Seriously though, these things take time, and if the gov't is the one in charge of it all, it takes more time than we'd like it to.

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Bushwhacked Glenn Posted: Feb 21 2005, 05:25 PM 

Satellite geometry may have been the most significant factor when the GPS program was young and there less satellites in ordit. But now there are enough satellites that coverage is not a factor. Now if you said receiver geometry I would have to agree 100%.

 

Semantics :) Never heard it called "receiver geometry" but we are talking the same thing here. A google search on "gps" and "receiver geometry" gives 219 results. Change that to "satellite geometry" and we get 8,060.

 

Satellite geometry refers to the positions of the satellites in relation to the receiver. A receiver's accuracy is affected by satellite geometry. The satellite geometry that provide the highest accuracy is when one satellite is directly overhead while the others are evenly spread around the horizon. A poor geometry is when the satellites are close together because they do not offer distinct positions for triangulation.

 

However, since we are relating this geocaching, receiver geometry shouldn't be a factor. One would hope that the cacher would be looking for the cache in the same area that is hidden.

 

Makes no sense. The satellites are in orbit (i.e. in motion) so the satellite geometry is constantly changing. Professionals in the field use software to determine the time of day when the best geometry for a given location will be so that they will get the most accurate coordinates when they are trying to be as precise as possible.

 

Before the L2 signal was made available ionospheric delay alone could cause as much as a 100 meter error.

 

Huh? We don't even receive the L2 on our receiver's. We receive the C/A code on the L1 frequency which currently gives us 10 to 20 meters. Ionospheric delay causes an average error of about 4 to 5 meters. The 100 meter error we use to get before May of 2000 was due to intentional dithering of the L1 C/A signal by the Dept. of Defense.

 

The L5 signal is going to be esentially the same as the L1 signal.

 

The L5 code will have 10 times the resolution as the L1 C/A code length.

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Semantics  :)  Never heard it called "receiver geometry" but we are talking the same thing here. A google search on "gps" and "receiver geometry" gives 219 results. Change that to "satellite geometry" and we get 8,060.

 

Satellite geometry refers to the positions of the satellites in relation to the receiver. A receiver's accuracy is affected by satellite geometry. The satellite geometry that provide the highest accuracy is when one satellite is directly overhead while the others are evenly spread around the horizon. A poor geometry is when the satellites are close together because they do not offer distinct positions for triangulation.

 

Having an OIC moment. :) I agree it's semantics.

Isn't the satellite constellation set up to avoid poor geometry?

 

Huh? We don't even receive the L2 on our receiver's. We receive the C/A code on the L1 frequency which currently gives us 10 to 20 meters. Ionospheric delay causes an average error of about 4 to 5 meters. The 100 meter error we use to get before May of 2000 was due to intentional dithering of the L1 C/A signal by the Dept. of Defense.

 

Do you have suggestion for websites to check out so I can read more about this. I'd like to learn more about the tech of GPS. All of the ones I'm finding don't go very far in to the tech side.

 

The L5 code will have 10 times the resolution as the L1 C/A code length.

How is resolution determined?

Edited by Bushwhacked Glenn
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Bushwhacked Glenn Posted: Feb 21 2005, 07:52 PM 

Isn't the satellite constellation set up to avoid poor geometry?

 

In general, yes. 24 active satellites gives very good coverage but that can't overcome you being down in a valley, among buildings or under heavy tree cover. In these situations the signals you are receiving are coming from sat's that are either relatively close to each other or in the same general direction from you and that's when accuracy suffers.

 

For websites, try Quest and Sam Wormley's pages. The Usenet group sci.geo.satellite-nav is also a good resource.

 

The resolution of the codes is determined by the number of elements in the code. The L1 C/A has 1,023 whereas the L5 will have 10,023 This is determined by different clock rates.

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It says that accuracy will be about 1-2 feet off currently it is about 10-15 feet off my GPS typically get within 70 feet off the cache before it starts going beserk but what really happens is that we have clouds trees sure they may be able to increase the signal under trees but it will still be off by quite a bit. I don't think it will be too much of a problem. :)

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How is  resolution determined?

The resolution normally quoted is the number of chips/sec used to encode the spread spectrum signal. (Kind of like bits/second, but it's not called that because there is no data sent at that rate. data is encoded on top of that at about 50 bits/sec)

 

Some receivers can use state change information on the carrier sequence to get a higher accuracy reading.

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"Oh, goody!" I hear you say. But I think perhaps it'd be a good idea if we discuss the implications this will have on our game. It's one thing when the GPSr tells you you're within 30 feet or so of a cache; it'll be quite another when it tells you you're within 2 feet.

Wasn't the intent of the 'first' geocache to see how close someone could get to a cache placed by someone else after SA was turned off?

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I have done some research on L5 and present day GPSRs. I have contacted Garmin International and asked if I needed to get a new receiver to use the new L5 signal. I was told that the L5 frequency is part of WAAS and if your GPSR is WAAS capable you will have no problem using it.

 

Also, if you don't like the idea of a more accurate GPS signal for Geocaching you could opt not to buy a GPS with WAAS or if you already have WAAS don't turn it on. :D

Edited by Gekobear
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Sounds hokey to me. While the FAA is adding L5 to the current GEO's, it is on an entirely new frequency of 1176.45Mhz which we will not be able to receive on our single frequency receivers. We will continue to get WAAS corrections on the L1 frequency of 1575.42Mhz which is the same freq that the "regular" sat's transmit on.

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