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A few days ago I followed some links into some info about GPS satellites and read that the satellites that supply the WAAS corrections are numbered above about 33 in the number system used in Garmin GPS units. Since then I've paid more attention to the satellite list in my nuvi 350. When I'm sitting at home I get 8-10 satellites numbered below 33 plus #48. The 48 bar is always empty (not colored in). Does that empty bar mean anything? The stuff I read also had some images of GPS units that showed a D in most of the bars representing each satellite and the article talked about the D indicating that WAAS was working, I think. I've never seen a D in my satellite list.

When I drove from Richmond Virginia to Norfolk the other day on a clear cloudless day I did not ever see any satellite number above 33 listed! The accuracy in my nuvi is usually indicated to be around 20-30 feet. I'm not sure I've seen it any better than that. Is that what you would expect? Am I getting any benefit from having WAAS turned on?

Thanks,
Bill

WAAS satellites transmit correction data but also act as normal GPS satellites which your receiver can use to determine it's position. The empty bar indicates that 48 which is still in test mode and is not transmitting "ranging" data which is used to determine your position.

The "D"s inicate that WAAS correction data is being received for that satellite. Your location on the east coast is currently not serviced by an active WAAS satellite so you may not be receiving correction signals and therefore not see "D" s on your display.

Since the last firmware update on my 76csx I have started getting 51 pretty regularly in central Alabama.

Jeff T

Thanks Chinook and Jeff. That reassures me that my Nuvi 350 is working as well as could be expected.

Bill

Yesterday, I put the Nuvi 350 near the window on the south-south-east side of my house and it picked up satellite 35, with a hollow signal strength bar. So, it looks like 35 is visible near the east coast too, and probably is also not completely operational yet. Is that the situation?

Thanks,
Bill

35 was originally off the east coast but was moved west over the winter (the FAA only leases space on regular communication sats). It was under going testing at the new location so this may be what you're seeing.

Bill there's something you might try. Included in the data that each WAAS satellite sends is information about the other WAAS satellites. Once your receiver has downloaded this "almanac" it may be able to find the new sat over the east coast. Go here and scroll down to the section on "Loading the Almanac".

Thanks for the info, Chinook. I'll follow that link and learn a little about almanacs.

Bill

Evidently the new unit with the sirf chips do not use the waas sats for the position fix, or so I have been told. Only for corrections.

Right and wrong. If it (the gpsr) believes the coordinates are worthless it won't use them. If I catch a satellite thats "nearby" i'll get coordinates, if I get stuck with one from the east coast or midwest I just get corrections. The bar changes colors accordingly.

The new Sirf chip CX model receivers differ quite a bit in how they handle WAAS from the older units. I have a 60cx. I used to have a map76. Here is how they differ. My question is why?

In the older unit, first of all, all the sats in the current almanac for that position would have a slot whether they were in view, being downloaded, or currently used or not. Not so the new units. Seems any sat only holds a slot if it is being downloaded or is currently used.

As to WAAS sats, older units held 2 slots for 2 WAAS sats. Those bars filled in only if they where being used for a position solution. The correction "D's" could be on a slot of any sat whether it was present and used or not. The WAAS sat could also be corrected. The "D's" would apply to whatever sat was corrected. They appeared individually. The ionospheric corrections, being universal, were still applied for 2 minutes after all the "d's" dissappeared, so the "d's" represented the other corrections that apply to each sat.

With the new units the WAAS (single sat) bar fills in and instantly all the "D's" on all the sats appear. The WAAS sat never is corrected. If the WAAS sat blinks out, even for a moment, all the "D's" dissapear at once and will all reapear if the bar fills in again. A blank slot never has a "D". A unfilled bar never has a "d" either.

Obviously things are not the same. Someone said that the WAAS sats no longer are used in the position solution with the new chip. Some else said they are (sometimes). Which is true? Why are the "d's" now all or none? and only there when the WAAS sat bar is up? I know that the ionosphereic corrections are universally applied and are kept for at least 2 minutes, and I know the other corrections should appear individually. So why not?

Hmm. Thinking about this I wonder if these displays are accurate or just a quick cosmetic fix to placate those yelling about the WAAS problems with the chip, though it could be that all this appears only when there is 100 percent correction. I know WAAS works in the units because I've experimented with it with benchmarks, and it is effective. But I can't figure out how it is currently being implimented.


--------------------

“When I am Playful I use the meridians of longitude and the parallels of latitude for a seine, and drag the Atlantic Ocean for whales” ~Mark Twain
~
“Consider the lines of longitude,
How they cover the Earth head to foot,
How they expand in the heat,
And contract in the cold,
But will always stay right where they’re put.” ~EraSeek

On my 60csx the d's are not all or none. Ihave a couple satellites that always miss the boat and have no d's.

same here on my 60csx in Atlanta, i get the "d's" all at the same time but there are any given two at a time that the "d" does not show up when the others display the d. always at least 2 without the d, never been 3 that i've noticed.

inside my house and i get satellite #51 regularly as well. he never gets the "d" but is full to the 3rd signal strength bar consistently.

a question i have though as a result of reading this thread, i gave a little more attention to the satellite's that i pick up, when the #51 shows up, its there for ten or 30 minutes at a time then disappears. it reappears but i'm wondering why, does it get bumped by satellites that give me a better signal? in some cases, the slot that #51 always shows up in (far right %100 of the time if there) when 51 is not there, the slot is blank displaying no satellite at all. and there is no satellite number there either, just the two blank underscore symbols. why is this? what's the deal, anyone, anyone, anyone, Beuller?

thanks

I have a 76C which I believe behaves differently from the x series units but I think you are right that if another WAAS satellite is stronger it may bump 51. Also remember that 51 is still in test phase so the signal may be turned off at times.


When you have WAAS enabled the GPS reserves a channel or channels for the WAAS satellites. On the 76C it starts with two channels but once it has a strong lock it drops one of the reserved channels so it can be used by regular satellites. IIRC the x series only uses one channel for WAAS