Re: Getting A Waas Lock

[+firefighterjake]

In the past few days I've noticed a problem with my Magellan Meridian Color GPSr and I don't know if it's just me or due to something I've done so I would appreciate any honest answers to this question.

 

I've been trying to get a WAAS lock and my GPSr won't establish a lock . . . the best I can get is EPE 16 feet. This makes it darn near impossible for me to do a cache hide as I want to have as good coords as I can get.

 

What I'm wondering is if anyone else has any similar problems . . . which could possibly point to a problem with the satellite.

 

Alternatively, has anyone else had this happen to them? I was up on a hill the other day with a whole lot of high-powered TV and radio transmitter antennas and was wondering if this could have done something to the GPSr unit.

 

For your information I live in Maine and have tried using the unit at various times of day, different locations and leaving it on for an extended time. On a recent trip to the north of Maine I didn't get a WAAS lock until I was 2 hours + into my trip.

[+geognerd]

Jake, your location in Maine is the problem. Take a look at this page about the changes in WAAS coverage. Officially you will be without WAAS coverage through the summer, though I think another satellite is undergoing testing and sending WAAS corrections for your area. Hopefully Peter or another more knowledgeable forum member will drop by and set me straight if I am wrong.

[+blindleader]

In the past few days I've noticed a problem with my Magellan Meridian Color GPSr and I don't know if it's just me or due to something I've done so I would appreciate any honest answers to this question.

 

I've been trying to get a WAAS lock and my GPSr won't establish a lock

 

It's because I stole your WAAS bird. Well, that might be the problem. The satellite you were probably getting WAAS corrections from before, is in the process of moving from the Atlantic to the Pacific, and has probably moved too close to your horizon for you to pick it up reliably. Fear not. More WAAS satellites are on the way later this year.

 

In the mean time. Don't worry about the accuracy of your coordinates, especially with 16 ft uncertainty. That's pretty good. Probably 99% of all the caches out there were placed without the benefit of WAAS. There are a number of techniques you can apply to try to improve your coordinates (and autoaveraging for ten or twenty minutes is not one of them).

1. Use mission planning / satellite prediction software to pick a time when the satellite geometry is best, and take your fix then. You still want to take a number of fixes just to make sure the one you use is not an outlier.

2. If the cache is in a place with identifiable landmarks nearby that can be seen on satellite photos, use USAPhotomaps to check your coordinates. In some urban areas, in some cases you can get a fix down to 1 ft this way.

3. If you were really a masochist, you could take an average of multiple readings, but the course in probability and statistics that you probably didn't take in college would tell you that the only way to get a valid average involves making multiple visits to the site at all hours of the day and night over a period of several days, recording your fixes, the received satellites, and exact times by hand, and then crunching the satellite geometry numbers to weed out the less than excellent fixes. An alternative to all this would be to hire a surveyor with differrential GPS to get a sub 1 meter fix in a short time for far more money than you want to spend.

[+GPSlug]

Jake, your location in Maine is the problem. Take a look at this page about the changes in WAAS coverage. Officially you will be without WAAS coverage through the summer, though I think another satellite is undergoing testing and sending WAAS corrections for your area. Hopefully Peter or another more knowledgeable forum member will drop by and set me straight if I am wrong.

 

More info from GPS World

The FAA notice doesn't tell the full story, however. Two new WAAS broadcasting

satellites launched last fall. PanAmSat (133W) began broadcasting in test mode

with corrections full-time this March, and Telesat (107W) is scheduled to

begin the same mode on or around April 1, 2006. The FAA announcement does not

take into account either of these broadcasting satellites.

 

So if your GPSr can be convinced to use it, and you promise not to try to land aircraft with it, you should be able to use Telesat (probably with PRN 138 (Garmin 51)) in Maine in a few days.

[planewood]

Here's another quote from that same GPSWORLD site.

 

"However, the FAA won't certify the accuracy/reliability of the new satellites until after extensive testing. Until then, non-aviation receivers may use the signals at their discretion —the same mode WAAS operated in prior to its July 2003 commissioning. Also, non-aviation WAAS receivers may not be configured to use the new test signals; check with the manufacturer."

 

So, are the Garmin units configured to use the new test signals? I'm guessing not cause I sure haven't seen any signals except for a hollor bar with #35.