How many satellites

After having read a post yesterday or some such about the satellite screen, I drove in to work today (about 45min) with the sat screen up.

As you say, it starts with about 3, and then is trying to acquire the unfilled in boxes. Most of my trip, I had about 9-11 filled in satellites with about 12 or 13 listed on the screen. Closest accuracy I got was 12 ft.

I'm not sure how the blinking unfilled in satellites are acquired. I had one unfilled but visible in the polar map for the entire trip until the last 2 minutes when it magically acquired. And, I was driving in a direction AWAY from that satellite.

Also, seemed to have sat numbers ranging from 2-51.
Not sure if those are arbitrary local-to-my-unit numbers or if everyone sees the same 'satellite 26' for example.

A minimum of 4 satellites are required for the GPSr to accurately determine its position.

The Garmin satellite signal screen displays each satellite using its unique id (PRN), which is assigned when the satellite is put into service. WAAS and EGNOS satellites are shown as PRN minus 87.

Each GPS satellite has a PRN in the range 1-32. There are 31 satellites (PRNs 2-32) currently broadcasting .

Each WAAS/EGNOS satellite has a PRN in the range 120-138. There are 2 WAAS satellites for North America, and 3 EGNOS satellites for Europe/Asia. Their Garmin ids are 48 and 51, and 33, 37 and 39 respectively.

The FAA has a very cool realtime satellite status web page at http://www.nstb.tc.faa.gov/RT_WaasSatelliteStatus.htm
This page can be used to verify the subset of visible satellites shown on the Garmin satellite signal screen.

Thanks for the FAA site -- nice presentation!

Thanks for alerting me to the number of satellites. I don't know why it's important, but it's neat. Some of my "bars" have a little "D" in them and others don't. Does anyone know what that means?

thx,
Jen

Thanks for alerting me to the number of satellites. I don't know why it's important, but it's neat. Some of my "bars" have a little "D" in them and others don't. Does anyone know what that means?

thx,
Jen

Which Garmin model do you have? Is WAAS enabled??

I've read that for some models (e.g. eTrex) the "D" on a signal bar indicates a WAAS satellite with correction data.

There are no "D"s on the signal bars of our nuvis (680 and 650) when WAAS is turned on.

In the Ique3600 manual it says for the little "D"

"Differential Navigation (D) with WAAS enabled"

My owner's manual for the 880 mentions WAAS only in the Appendix, under specs, where it says: "GPS receiver- high sensitivity, WAAS-enabled." I learned the hard way that while my Blackberry Curve was "GPS-enabled" that only meant it COULD HAVE IT...but did not have it built-in. That's why I am skeptical of generalities in product descriptions.
Jenny has the 880 like mine, but I see no little d's on the satellite page.

I would like to know more about what difference I can expect from being WAAS-enabled, so I will go make friends with Wikipedia.

Your help is invaluable, believe me. Thanks

WAASup, I found an illustration of the sat page with "D" on the sat bars, at this location: http://www.gpsinformation.org/dale/dgps.htm#WAAS

The whole reference to it came from the Wikipedia link you put in this conversation earlier. I'd like to quote a little from it, and then ask a question afterward:

"However, unlike the standard GPS almanac that is preloaded into each Garmin receiver, the WAAS almanac is not loaded into the receiver when you get it. Each person is required to get the almanac for themselves and this is required before it can be used in WAAS mode. Some folks are able to get an almanac fairly quickly while others struggle for days and are still not able to get a successful load. Here is the technique that will result in obtaining the almanac in the minimum amount of time. "

Now, I copied and pasted the next bit of instructions to a WORD document and saved it, just in case I have to load that almanac. (At this point, I can see that I am getting way over my head.) First of all, does our GPS consumer-grade have a file called GPS almanac on it, and do we need to load the WAAS almanac to really use the WAAS capabilities of the unit?

The source says that sats with #s >#32 are WAAS. I have not located any numbers >#32 on my sat page.
I do not know if any Garmin techie can be relied on to give an informed explanation or not.

Meanwhile, I have on my sat screen a little red ball on the outer ring which continues to go back and forth after going from noon to 6, and the 880 is not moving--it is stuck to the north facing window.

BTW, it did say in this article that you'd do better with a south-facing exposure at higher latitudes. I suppose 43 North lat is a higher lat.

Just some observations...

I have a eTrex Vista HCX. When I view the Satellite Page, I find the red dot at the outer ring indicates the direction the unit is pointed when the internal compass is turned on. With the internal compass off, the red dot indicates the direction of travel and not the direction the unit is pointed. If I am not moving, the dot is somewhere between stable and erratic, depending on the signal strength (I think ) and random variations.

When I first turn the unit on, the "D"s are not shown but show up after awhile. Once again, I think this happens after certain data is received. Bird #51 never shows the "D". Also, if I turn the WAAS receiver off, the "D"s are no longer shown in the display.

A minimum of 3 satellites is required for a 2D fix (no altitude) and 4 satellites for a 3D fix.

The accuracy of the fix is very defendant on the geometry of the satellites being received. For example if you're in a canyon with steep sides (or an urban canyon in a city with large buildings), the satellites you're receiving may all be in a "straight line" and your position accuracy will be poor.

Current GPS chips do some fancy stuff like storing almanac data and projecting it into the future for fast first fix times after turn on but if you're seeing "unfilled bars", it probably means the GPS is downloading current almanac data before the satellite can be used for navigation.

It takes about 30 seconds to download the almanac for a sat. Modern GPS receivers can receive parts of the almanac out of sequence when reception is interrupted such as in a moving vehicle traveling past obstructions but that can still greatly extend the time it takes. Leaving the receiver motionless with a view of multiple sats for the first minute can often be very helpful.

My first GPS was the Garmin GPS45 (still have it) and it had an 8 channel multiplexing receiver and required 30 seconds for each satellite to get the almanac after a cold start. But that was years before selective availability was turned off...

Mike

[quote=SummermugJust some observations...

I have a eTrex Vista HCX. When I view the Satellite Page, I find the red dot at the outer ring indicates the direction the unit is pointed when the internal compass is turned on. With the internal compass off, the red dot indicates the direction of travel and not the direction the unit is pointed. If I am not moving, the dot is somewhere between stable and erratic, depending on the signal strength (I think ) and random variations.

When I first turn the unit on, the "D"s are not shown but show up after awhile. Once again, I think this happens after certain data is received. Bird #51 never shows the "D". Also, if I turn the WAAS receiver off, the "D"s are no longer shown in the display.

On the C530, WAAS is turned on/off by going to Wrench > System > GPS Mode and selecting WAAS/EGNOS.

Seem strange that you can't turn WAAS on/off. (I have seen features dropped in software updates. Although, it may not have been planned.)

On my System, it only shows:
GPS Simulator (off/on)
Usage Mode: (auto/bike/pedestrian)
Units: (miles/km)
Keyboard: QWERTY
Remote: (activate/deactivate)

Then at the bottom, it has "About" where you click to view the software versions and the licensing agreements on the unit.

My software on this unit IS out of date, but I have not downloaded the update, because I don't know where to install it. I cannot identify the file.
I have 2.50 and I need 2.80...... Webupdater cannot do it for me, it said when I tried.

Try this...
1.Plug the unit to the USB port.
2.Open/start WebUpdater.
3.Click on Next>
4.Wait one while it finds the device (something like GARMIN (E:\)
5.Click on Next>
6.Click on 'Proceed to check for additional updates such as voice updates.'
7.Click on Next>
8.If there is a new version, it should be at to top of the list. Check the box.
9.Click on Next>
10.Since I'm up to date, I can't give you the details, but it should download the file to your unit. This may take sometime based on the speed of your internet connection. Be patient...

After the file is downloaded to your unit, disconnect the USB port. That will restart the unit and you should see a message that the software is being loaded.

Maybe someone else could fill in the details???

Let us know how you make out.

This may or may not solve turning WAAS on/off.

When I received my 880, and in fact both of my 880's did the same thing. Web updater did not find my garmin connected to my pc. So when I d/l the actual 2.80 and ran it manually as an administrator in Vista, I was then able to use updater since then. So d/l the file and manually install the update and then you should have no problem with your computer recognizing your garmin via webupdater.

If I manually download and send it to the 880, where would I put it? I have Windows XP SP3 running on my computer. My husbands computer does have Vista. Should I try it with his Vista computer?

Yea, the WebUpdater didn't find my Garmin, even though the computer itself had it listed as the E:drive.

Thanks for the info about your experience with this unit.

This advice is clear and logical, and I will keep it for future reference. Right now, WebUpdater cannot find my Garmin, so I am out of business with that approach.

The following info might solve your problem. I had the same problem with my nuvi 850 & it worked for me. I found this buried somewhere in Garmin's Knowledge Base.