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GPSMAP76 and WAAS

Old 11-19-2002, 06:46 PM
  #1  
edk
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Default GPSMAP76 and WAAS

I recently bought a GPSMAP76. I have been unable to lock onto a WAAS satellite yet. I initially thought that it was a problem with line of sight to the satellite. I have not been able to use it on open water yet - just in my back yard. I can see satellite 33 register in the satellite status display, but the unit never locks onto it.

Yesterday I hooked up the Furuno NAVnet plotter that I just bought and tested it alongside the handheld. It immediately locked onto a satellite that it identified as 122 and got a WAAS fix straight away. The handheld showed exactly the same satellites as the Furuno, except that it was trying to lock on to satellite 33, where the Furuno had successfully locked onto satellite 122, and did not acknowledge the presence of satellite 33.

Are these two satellites the same or are the two units receiving different signals? Should the handheld be locating satellite 122 also?

Does anyone else have problems locating WAAS satellites with Garmin handhelds. The GPSMAP does have the WAAS option enabled and has been upgraded to the latest software version (2.09)

Ed
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Old 11-20-2002, 02:17 AM
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Default GPSMAP76 and WAAS

WAAS corrections are only broadcast from 2 satellites. PRN 122 (AOR-W) and PRN 134 (POR), which in Garmin (NMEA convention) terms are #35 and #47.

Location and line of sight is everything with WAAS and obviously the Furuno has an external antenna and the 76 being a handheld could struggle a little depending on the obstructions compared to an external antenna.

Satellite #33 (Garmin terminology) is satellite PRN 120 (AOR-E) to the west of africa and totally useless in the U.S as far as WAAS is concerned.

Cheers, Kerry.

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Old 11-20-2002, 04:53 AM
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Default GPSMAP76 and WAAS

I was unaware that WAAS was only on basically two satalites unless you're in Africa. Where did you get that information from...not an Garmin site or did I miss it? Thanks [img]/infopop/emoticons/icon_redface.gif[/img] [img]/infopop/emoticons/icon_rolleyes.gif[/img]
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Old 11-20-2002, 05:02 AM
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Default GPSMAP76 and WAAS

On the GPSMap76 the dafault setting in the setup is for the WAAS to be turned off. That is done to increase battery life. Did you turn yours on? Also, if you did turn it on, if you did anything like load updated software it will revert to the default, off, position.

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Old 11-20-2002, 05:47 AM
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Default GPSMAP76 and WAAS

I did turn WAAS on after downloading the latest software. Satellite 33 does not appear on the status display if I turn WAAS off.

The Furuno does have an external antenna, but I just took the GPS out of the box and hooked it up to a battery on my patio (Don't have the boat yet). The Furuno antenna was laying on the same table as the Garmin handheld, so had the same line of sight. There are no tall buildings nearby to obstruct the horizon, just single story houses and some trees. This is looking like a problem with the handheld. Can anyone with a Garmin WAAS enabled receiver tell mne what the WAAS satellites show up as on the GPS status display and how long it takes to lock on to them? I believe 33 is an EGNOS satellite, which as Kerry said would be useless to me in the SE US.

Ed
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Old 11-20-2002, 06:32 AM
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Default GPSMAP76 and WAAS

Don't look for the bird itself. Just look at the bottom of each individual status bar. When each of them goes dark if there is WAAS correction being received for any particular bar a very small lette "D" will be inside the status bar at the bottom.

Thom

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Old 11-20-2002, 08:21 AM
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Default GPSMAP76 and WAAS

quote:Originally posted by Thom:
Don't look for the bird itself. Just look at the bottom of each individual status bar. When each of them goes dark if there is WAAS correction being received for any particular bar a very small lette "D" will be inside the status bar at the bottom.

Thom

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How what? If you are asking how I turned on WAAS I went to the setup menu and enabled it.

I understand that I will see a "D" when I am receiveing WAAS corrections. The problem is that I don't see the "D". Nor do I see the "GPS Differential" status that I should see if I have a WAAS fix - only "GPS 3D". Nor do I see a WAAS satellite on the display.

Why should I not look for the satellite? I cannot get a WAAS fix unless I have one in sight. Interestingly, I looked at the Garmin support page and they say that it will take up to 20 minutes to lock onto the WAAS satellite(s) and another couple of minutes to process the data to provide a WAAS fix. Is that what Garmin users are seeing? (The information was for eTrex users - they had nothing specific for the 76). My Furuno locked onto the satellite almost immediately. I know that the patch antennas in the handhelds are less sensitive, but I wouldn't expect that kind of difference in reception.

How long is it taking you to acquire a WAAS fix?

Ed
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Old 11-20-2002, 08:41 AM
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Default GPSMAP76 and WAAS

I just went out into the parking lot and checked. It was quick. It took 16 seconds to get a position fix and then an additional 8 seconds to pick up the WAAS corrections. At no time did the status bar say anything abuot WAAS though, it just contined to read 3D ..... (whatever it says). I was out in the open, no trees for a couple of hundred feet, and no large hills within a mile or so. I'm in West Virginia, about 70 miles SSE of Pittsburgh.

Thom

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Old 11-20-2002, 11:06 AM
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Default GPSMAP76 and WAAS

If it says 3D Differential, that means it has a WAAS fix. If it says 3D GPS it does not have a WAAS fix. I have never seen 3D Differential diplayed on mine. I will send Garmin an email tonight.

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Old 11-20-2002, 11:33 AM
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Default GPSMAP76 and WAAS

Don't get me wrong, I almost never look at the status page, but I don't remember every having seenmine say "3D-Differential". That's not to say it hasn't given that message, its just that I don't recall ever having seen it. Let me know what you hear from them, and I'll leave mine on the status page for the drive home this evening and see if it ever says ... Differential.

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Old 11-20-2002, 11:51 AM
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Default GPSMAP76 and WAAS

I was looking at the manual - http://www.garmin.com/manuals/96.pdf - page 25 and page 58 refer to the "Differential" status when receiving WAAS. It says that you need to be getting WAAS corrections on 4 or more of the normal GPS satellites (for 3D differential).

If you do check, could you also see if you are locked onto either satellite 37 0r 45. I'll let you know what I hear from Garmin.

Thanks,
Ed
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Old 11-20-2002, 03:33 PM
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Default GPSMAP76 and WAAS

Well, when I left work today it fired up at about normal speed, and within a couple of seconds the little letters "D" appeared at the bottom of the status bars .... but it wasn't showing 2-D or 3-D Differential. So I drove away and it took it about a minute and a half before it switched over (once again, still on the Status Page) and the magic word Differential popped up. I had never paid a bit of attention to that before, having just assumed that if the little "D" was there it was acutally using the WAAS corrections. Live and learn I guess. Anyway, yes, mine does pick them up on sattelite number 30-something but it takes a little while for it to take hold, so to speak.

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Old 11-20-2002, 03:39 PM
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Default GPSMAP76 and WAAS

quote:Originally posted by Mumblerone:
I was unaware that WAAS was only on basically two satalites unless you're in Africa. Where did you get that information from...not an Garmin site or did I miss it? Thanks [img]/infopop/emoticons/icon_redface.gif[/img] [img]/infopop/emoticons/icon_rolleyes.gif[/img]

WAAS corrections being only broadcast from the those 2 WAAS (inmarsats) satellites is one of the bad links in the system, totally no redunancy what so ever.

It would only take one of those satellites to malfunction (both don't give full US coverage anyway) and things would not be good. The lead up time to put another one in the air could be as long as 3 years [img]/infopop/emoticons/icon_eek.gif[/img]. Having only 2 sats (without redunancy) is a real bottleneck for WAAS to be become fully operational.

In Africe (like Australia) WAAS is useless anyway, just that the signal can be receieved but all it does is blow the accuarcy off the scale, due to the ground station setup and atmospheric corrections data.

PRN 120 (AOR-W) & 131 (IOR) Garmin #'s 33 & 44 respectively would be the EGNOS corrections but that's no good in Africa, Australia or the U.S for that matter either.

Cheers, Kerry.

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Old 11-20-2002, 05:07 PM
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Default GPSMAP76 and WAAS

The little 'D' on the status bar says you've got a WAAS satelite, no problem. However, the 2-D and 3-D has nothing to do with WAAS. It means that you have at least two sats so lat and lon is OK, when the 3-D comes on it means that you now have three sats, so you now have elevation, too. I'm going from memory here, the unit is on the boat and so is the manual. I have a Garmin GPSMAP 76S. Am I wrong? [img]/infopop/emoticons/icon_razz.gif[/img]
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Old 11-20-2002, 06:34 PM
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Default GPSMAP76 and WAAS

quote:Originally posted by Mumblerone:
The little 'D' on the status bar says you've got a WAAS satelite, no problem. However, the 2-D and 3-D has nothing to do with WAAS. It means that you have at least two sats so lat and lon is OK, when the 3-D comes on it means that you now have three sats, so you now have elevation, too. I'm going from memory here, the unit is on the boat and so is the manual. I have a Garmin GPSMAP 76S. Am I wrong? [img]/infopop/emoticons/icon_razz.gif[/img]

The "D" means that differential (WAAS) corrections are being made to that satellite. It is not a WAAS satellite - it is a regular satellite that the WAAS satellite is able to provide correction information for.

There are four different status codes:

2D GPS - only using three satellites - no altitude reading available

3D GPS - using at least four satellites - altitude available

2D Differential - WAAS differential data being used on 3 satellites.

3D Differential - WAAS differential data being used on at least 4 satellites.

There are only two WAAS satellites - the data from them is used to correct data from the regular GPS satellites.

Ed
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Old 11-20-2002, 06:41 PM
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Default GPSMAP76 and WAAS

Cool...thanks! [img]/infopop/emoticons/icon_redface.gif[/img] [img]/infopop/emoticons/icon_wink.gif[/img]
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Old 11-20-2002, 07:12 PM
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Default GPSMAP76 and WAAS

Mumblerone, link showing the footprint of the WAAS sats AOR-W (over Brazil) and POR (Pacific).

http://217.204.152.210/support_maps.cfm

Basically loss of AOR-W and WAAS coverage for the biggest part of the U.S for the time being is dead.

The following link better answers your query (just had to find it) and also highlights the potential failure point in the whole system at present.

http://gps.faa.gov/CapHill/geosat.htm


Cheers, Kerry.

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Old 11-21-2002, 08:33 AM
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Default GPSMAP76 and WAAS

edk, kerry is right on, the WAAS satelite is 35 and not 33. I can't give you realtime feedback, but I can tell you that I have no problem picking up 35 on either my 2006 or 182, both external antennas. And that is from Key Largo. It should appear in the Southeast quadrant. It always seems to be the last sat to lock-on, which I guess is normal.
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Old 11-21-2002, 09:06 PM
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Default GPSMAP76 and WAAS

I had a reply from Garmin, but they didn't seem to understand the problem. I told them that I had used my Furuno GPS to compare performance and they replied that the Furuno probably had a more sensitive antenna. I have asked them to look into the fact that my GPSMAP is communicating with the wrong satellite, so antenna sensitivity is irrelevant in this case. I was able to confirm that the two receivers were actually communicating with totally different satellites.

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Old 11-22-2002, 09:11 AM
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Default GPSMAP76 and WAAS

edk,
I think you have a software problem OR your 76 does not have a clue where you are. If it doesn't know where you are, it cannot give you the correct array of sats. Sounds to me like the 76 thinks it is still in Kansas.
I happen to have my 182C here in my office in Miami and connected to my PC. No antenna on the 182C. However, my sat display is showing 1,2,3,13,14,20,25,31 and good old 35. Over the last 5 minutes, my array has changed to 1,2,3,13,20,25,27,31 and good old 35. Note that I have lost 14 and gained 27.
Anyway, that is a laymans observation. Check it out.
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