GPS satellites on the blink?

[fishdirt]

Two , possibly three, caches I have hit recently have been way off on their co oridinates. Not 12 or even 20 feet but closer to 30 and 50 feet.

 

Before anything is said about my GPS unit (just the yellow etrex) my friend just purchased a better unit and we had a problem today. Right when we decided to give up he walked about 30 feet away and accidently found the cache.

 

So here's the question, are there certain conditions that can throw a gps off? Like weather or satellite upgrades?

[+TakeTheLongWay]

30-50ft off isn't that far off normal.

 

Remember the inaccuracy of the hiders GPS and yours in finding it can give your differences this big. IE if the hiders GPS is 20ft off, and your is 20ft off, its going to look like the cache is 40ft off.

[+Kryten]

In order to get a good quality fix you need a constellation of satellites visible in all directions. There are times however when all of the visible satellites are bunched together in the same part of the sky. When this happens accuracy can be considerably degraded. A quick look at the satellite page of your GPS will confirm if this is the case.

[+Isonzo Karst]

Signal can be degraded by radiation as well. That's what WAAS is supposed to help with.

 

WAAS corrects for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and it provides vital integrity information regarding the health of each GPS satellite.

 

But the WAAS signal itself can be weak, depending upon your location, or you may have it turned off. That both units were having trouble suggests that the signal was damaged

[+simplyred]

Makes sure your unit is not on battery saver mode, it lowers the units accuracy.

[+sundogranch]

If the hider of the cache dosnt check the coords by Marking the spot and then hitting Goto, the coords can be way off. I can get accuracy of about 6' by doing this. Often the GPSr will bring me to a spot 20' to the West. I will then subtract a few points from the West coords and try again till it brings me right to the cache. Every cache hider should do this. Also keep your GPSr ON between caches. Happy Caching!

[+quadcity007]

Yea, definately sounds like user error to me. HA!!!!

[+TheAlabamaRambler]

If it is any consolation I found my first 600+ with an eTrex Yellow, and if I had to give up my fancy 60CSx and revert to one today I don't think it'd be any big deal as far as actually finding the cache.

 

The most important thing you can learn about any GPS is to put it in your pocket when it gets you within 20' or so and let your eyes and intuition do the finding!

[fishdirt]

Yea, definately sounds like user error to me. HA!!!!

 

Actually I'm not an idiot. I took into consideration various factors including the unit, batteries, verse previous caches and the hiders of the caches as well as other seekers.

 

Compared to previous caches it's been way off on the the last couple. One cache that it was way off can be contributed to the hider of the cache as previous posters show difficulty with the coords being off.

 

With recent weather conditions and the logical presumption that satellites are constantly moving in orbit I was curious as to whether there were prime conditions or not. This is all I wanted an answer to.

 

I have to look into this WAAS thing. I think I have my answer though. Thanks

[+whistler & co.]

Yes...satellite reception DOES seem to be poor these past few days. We hid a new cache and followed our usual procedure for marking a bunch of coords, only to get home and find that the range between the highest and lowest sets were a couple of hundred feet difference. Furthermore, several logs for local caches (some ours, some that belong to other people) have had "coords off 50'" and similar comments. Some of these are caches where previous commets included mentioning how accurate the coords are. I think something is definitely up...maybe the new GPS satellite that was launched a few days ago is sending out weird signals or something!

 

New GPS Satellite

[+Vinny & Sue Team]

Two , possibly three, caches I have hit recently have been way off on their co oridinates. Not 12 or even 20 feet but closer to 30 and 50 feet.

 

Before anything is said about my GPS unit (just the yellow etrex) my friend just purchased a better unit and we had a problem today. Right when we decided to give up he walked about 30 feet away and accidently found the cache.

 

So here's the question, are there certain conditions that can throw a gps off? Like weather or satellite upgrades?

I suspect that you have not been caching for long! An error of 30 to 50 feet, particularly in an area which has hills, mountains, lots of trees, and other foliage, such as Michigan (where you are located) is not at all unusual. About the ONLY place where I expect accuracies within a few feet is in the Southwest, in areas with little foliage, no hills and no mountains which would block satellite signals, and even there, I often find that caches are located some 30 feet from "ground zero".

[+whistler & co.]

I suspect that you have not been caching for long! An error of 30 to 50 feet, particularly in an area which has hills, mountains, lots of trees, and other foliage, such as Michigan (where you are located) is not at all unusual. About the ONLY place where I expect accuracies within a few feet is in the Southwest, in areas with little foliage, no hills and no mountains which would block satellite signals, and even there, I often find that caches are located some 30 feet from "ground zero".

 

30' or so is not too bad, but we regularly get to within 10' or less of caches according to the GPS and based on where we actually spot the container.

 

Our new cache that we were trying to take coords for is on top of a hill, in the wide open, with a few leafless trees in the area but nothing else to interfere with satellite reception (not that a few leafless trees are that much of a problem under normal circumstances). Of course, it is in a cemetery.

[fishdirt]

I suspect that you have not been caching for long! An error of 30 to 50 feet, particularly in an area which has hills, mountains, lots of trees, and other foliage, such as Michigan (where you are located) is not at all unusual. About the ONLY place where I expect accuracies within a few feet is in the Southwest, in areas with little foliage, no hills and no mountains which would block satellite signals, and even there, I often find that caches are located some 30 feet from "ground zero".

 

30' or so is not too bad, but we regularly get to within 10' or less of caches according to the GPS and based on where we actually spot the container.

 

Our new cache that we were trying to take coords for is on top of a hill, in the wide open, with a few leafless trees in the area but nothing else to interfere with satellite reception (not that a few leafless trees are that much of a problem under normal circumstances). Of course, it is in a cemetery.

 

Diddo. I haven't been off more then 20 feet in my previous caches and caches I did with a friend. Interesting about the new satellite. I've made my adjustments for the hunts but it seemed real odd to me that all of a sudden things went a bit haywire.

[+kwitsman]

I've found that a few times, it depends on which brand of GPS that the hider uses too. If the hider uses a Garmin, I can zero right in on it with my Garmin. If the hider uses a Magellan, then I am off by 20-30 feet to the west of the cache. So if I don't find it right away, I start moving east. One local team has put out a lot of caches using their Magellan so now if I go for their caches, I just start looking to the east when I get close.

Karl

[+MACH1SCJ]

I am still new at this as well. Tonight my GPSr was bouncing around by 50 ft at multiple locations. Has never been that unstable before. I had 9 plus locks counting WAAS. However I did not check thier locations. (They may have been bunched)

[+Star*Hopper]

I'll resist my first temptation to offer the tip that, "If you have it set to 'Operate with GPS off' option, that can really play hob with readings!!"

 

But seriously, I'm glad to hear someone else mention this, 'cuz I've had some unusually weird readings the last 3-4 days too! I've been scouting cache sites, and recording coordinates - and going back the following day to confirm, & getting considerably different readings anywhere from 30-70' off from previous 'marks'. So much so, I've held off registering 4 new caches until I can get consistant numbers - all of which I wanted to have out by this Easter weekend. (And yes - one of them a decorated, egg-shaped container! Bummer.)

 

One notably strange reading I intended to ask about anyway, which is what led me to this thread. Initial mark made with 9' accuracy.....walked away 4 different directions & returned.....all dead on the money, so didn't even do my usual 5th check. (This last weekend.) On confirming yesterday, I's getting between 9 & 13' accuracy when I was a distance away from the GZ - but the closer I got, the farther the accuracy drifted....and we're talking 60-70-80'! Same thing happened today. The only interfering object was a 1-story building 50' away, & it to my north - clear open ground all around otherwise. Best accuracy I could get was 23'....and soon's I took a couple steps toward GZ the accuracy would start climbing quickly.

 

What was especially confusing was - I was picking up full signals from 8 of the 12 satellites on the display, and every one with the li'l 'D' indicating WAAS was adjusting.

 

All I know to ask is - WTH??!!?? Any ideas?

 

~*

[+root1657]

Two , possibly three, caches I have hit recently have been way off on their co oridinates. Not 12 or even 20 feet but closer to 30 and 50 feet.

 

Before anything is said about my GPS unit (just the yellow etrex) my friend just purchased a better unit and we had a problem today. Right when we decided to give up he walked about 30 feet away and accidently found the cache.

 

So here's the question, are there certain conditions that can throw a gps off? Like weather or satellite upgrades?

 

Not so long ago I had to learn WAY more than most people would ever want to about the actual workings of GPS for work... I was working a GPS project.

 

Long answer short, that little yellow do-dad you have is doing the same math on the same satellite signals as the rest of us and the fancier models. The only way you are getting a different signal is if you have one of the military recievers that recieves different signals, and includes the super cool crypto to use the military only super accurate signal.

 

The simpilest thing that can throw you off accuracy is weather. Radio waves bend when they go through the air (actually the water in the air), and if they bend one way one day, and the other way the other day, you can get double the error from the actual spot, if he was off one way when he placed it and you were off the other way when you were looking. WAAS can help this, by measuring the local effects of the distortion on the signal, and broadcasting a signal from a fixed point that tells your reciever "hey, if you are close enough to get this signal, correct yourself x feet in that direction".

 

There is also a canyon effect where a signal bouncing off one side of a canyon can mess you up pretty good. Usually it is a drastic and very powerful effect where the GPSr clearly has no idea where it is anymore and will bounce wildly around in large measures (way more than the typical few feet when you get to GZ). Those of us who cache in the city often have to deal with 'urban canyon effect' when we get close to big buildings, especially the ones with metal that can bounce signals.

 

Trees and stuff like that overhead messes with you because of the water in the plant. GPS signals are actually amazingly weak, and it's a wonder it works at all, so the water in plants can sheiled it pretty effectively.

 

So back to the short answer.... your unit is fine. All the extra bells and whistle options are nice, but in the end it's the same math on the same signals, so you should end up at the same zero.

 

Best advice I could give is to go close to zero (unit will usually bounce within 10 feet or so on a beautiful clear day), then start a search out to about 20 feet in all directions. If that doesnt do it, step back about 50 feet and see where the arrow points, then go off to one side and do it again. Sometimes it's easier to see where those two lines cross than to actually find zero.

 

Lastly, yes, there is something that they can do with the satellites that will ruin a good day of caching for all of us. There is a function called selective availability where they can actually degrade the accuracy of the unencrypted GPS signals by some amount they want to, and only the encrypted military units will get high precision data. Usually this would be reserved for combat, and can be done by region, to deny the enemy the use of our own GPS system while we still get to use it for our guys. I am only fairly certain that I have observed this one time, and it wasnt subtle... I was actually in a place where GPS had been working fine, then suddenly a dozen different GPSr of a few different types were all way off, in the same wrong location, but the military recievers that had the key loaded were still dead on accurate. Only lasted a few hours, so fear not, and cache again another day.

 

At the end of the day, just have fun! it's about the searching, not the finding.

Edited March 23, 2008 by root1657

[fishdirt]

Hmm. I had a theory about water and the radio waves being sent but it purely based on the fact that the places that were off were right next to either a lake or a big river. Awesome, this would explain the trouble. Reading up on the GPS satellite launch as well , the older satellites are in orbital decay of the final stage so that may make signals weaker around such as areas as woods, through weather and bodies of water.

 

Thanks!

[+Star*Hopper]

Ummm....Mr Fish, suh? If rivers & lakes are affectin' your signal, you're looking too deep!

He's talking about signals being blocked, bounced & bent as they come down thru the sky - not up off the ground.

 

And your conclusions about "older satellites are in orbital decay of the final stage" being the explanation for "the trouble"......well.......no. Satellites are always "falling" (the ones in orbit, anyway)....and frequently being boosted back into position. And they're high enough (roughly 12,500 miles - by comparison the ISS orbits at roughly 250 miles altitude) to where their gravitational 'slipping' is far from sufficient to lower their signal -- that only happens when they get far enough away to be over your horizon from your viewpoint. And they'd still be sending the same, steady signal to those within line-of-sight. Plus, they are positioned such that as one or more leaves view, others are coming into view. It only takes 3 to triangulate your position - and most civilian receivers I'm aware of will receive up to 12 if they're available (ie, in clear view).

 

Clear skies!

~S*H

[+Captain Jack Sparrow Sav-vy?]

I thought i was goining nuts, everytime i tried a different cache it was way off. I have been very lucky in my past trips but yesterday 3-22-08 was the worst i have ever had things off. Cloudy day but wow never 50' or more off. This forum was very helpfull and now i know more about my hobbie than i did before.

[fishdirt]

Ummm....Mr Fish, suh? If rivers & lakes are affectin' your signal, you're looking too deep!

He's talking about signals being blocked, bounced & bent as they come down thru the sky - not up off the ground.

 

And your conclusions about "older satellites are in orbital decay of the final stage" being the explanation for "the trouble"......well.......no. Satellites are always "falling" (the ones in orbit, anyway)....and frequently being boosted back into position. And they're high enough (roughly 12,500 miles - by comparison the ISS orbits at roughly 250 miles altitude) to where their gravitational 'slipping' is far from sufficient to lower their signal -- that only happens when they get far enough away to be over your horizon from your viewpoint. And they'd still be sending the same, steady signal to those within line-of-sight. Plus, they are positioned such that as one or more leaves view, others are coming into view. It only takes 3 to triangulate your position - and most civilian receivers I'm aware of will receive up to 12 if they're available (ie, in clear view).

 

Clear skies!

~S*H

 

This is also a valley region where many water levels are above locations I've been to that had the problem. Either way, I got the answers I was looking for on that. I'm aware of trees and always co-ordinate under a clear shot to the sky.

 

As well, read the article on the new gps launch. I did mention FINAL stage. They do not get boosted back according to that. Like all other satellites they are allowed orbital decay. The satellites that are getting close to falling are 14 to 15 years old. I'm going by the article mentioned earlier.

[+Star*Hopper]

 

...As well, read the article on the new gps launch. I did mention FINAL stage. They do not get boosted back according to that. Like all other satellites they are allowed orbital decay. The satellites that are getting close to falling are 14 to 15 years old. I'm going by the article mentioned earlier.

^^^^^^^^^^^

 

Errrmmm.....Mr Fish, Suh.....wid all due respeck, Suh, suggest you "go by" the article again yo'self, & take another look....maybe this time with da readin' glasses? It's "faIl", vs "faLl". First one goes 'sputter' & gets quiet....second goes "boom" & makes fireworks. "Fail IN orbit..." is a clue.

 

(I'm an astronomer; 50+ years....know a teensy bit about them.)

Clear'ns!

~Star*Hopper

StarHub Observatory

NeuseWay Planetarium

~Retired

Edited March 23, 2008 by Star*Hopper