Newbie seeking advice on a) EGNOS and b) antenna performance

cryptogam

Hi,

I'm actually seeking advice for buying a handheld GPS device but looking through these forums it looks like you guys might have the expertise to help - and also some of the units I am considering buying are reviewed on this site.

My questions are these:

1. Is this EGNOS thing fully operational yet? If yes, does that mean that if a buy a unit that claims "WAAS enabled" that I will actually get better accuracy than I would with one that doesn't have it? (I would be using the sysytem and W and N Scotland, BTW.)

2. Does the type of antenna the unit have make any real difference to the probability of getting a fix if there is partial sky obscuration - e.g. under widely spaced deciduous trees.

For information, my principal application would be plotting positions of rare plants encountered on botanical surveys. A lot of my colleagues use the basic Garmin e-trex - but it can be difficult to get a fix under trees. I am considering that a slightly more expensive model such as The Garmin GPS 76 might give better results (and better accuracy with EGNOS on). Any thoughts?

Thanks in advance,

Joe[/i]

matty2767 · Regular Visitor Joined: Jun 27, 2004 Posts: 85

i have had my gpsmap 76s for 2 weeks now and the waas hasnt been received yet even though i have set it to be enabled. (i am located in the east midlands).

the 76s uses a different type of antenna so gives a better fix and will hold it better. check out the reviews of units on this site. http://www.pocketgpsworld.com/garmingpsmap76.php

the best accuracy i have had is about 18ft.

cryptogam · Posted: Thu Jul 15, 2004 11:24 pm Post subject:

Thanks Matty,

So if I understand you right, at present you don't actually get any more bang for your buck using the 'WAAS-enabled' systems in the UK.

I wonder if people feel that its likely that there will be a benefit in the future? And if so, when?

Good to hear that the antenna on the GPSMAP 76s gives a better fix (presumably compared to internal patch' type antennae provided on the cheaper Garmin models). From my reading of the specs, the antenna on the Garmin GPS 76 would be identical to the one you are using, right? - please correct if wrong!

Cheers,

Joe

matty2767 · Regular Visitor Joined: Jun 27, 2004 Posts: 85

for the waas info i dont really know enough about when it will come operational in the uk to give you a good answer. have you tried doing a search on these forums?

if you check out the garmin website you can do a product comparison on all the models the gps76 and gpsmap76s have Standard GPS Antenna Built in - quad helix whereas the etrex doesnt.

http://www.garmin.com/outdoor/compare.jsp

matt

Skippy

I don't think EGNOS is fully operational at the moment, but it is running in test mode and you may be able to get a 3D-Differential fix from it.

My Garmin GPS-V claims the fix is accurate to 7 feet (17 feet without WAAS). This is in an area where I get very good reception though - I can easily get a lock on 12 sats.

The WAAS sat is very low in the eastern sky, you need a good view of the sky to pick it up. Even if you do pick it up, it takes about 15 minutes to get the correction information for all the visible sats. It slows down the map display on the Garmin GPS too - I leave it switched off.

As for getting a fix, WAAS only works in ideal conditions. Boats and planes won't have much problem but unless you have a clear view of the sky then you have no chance.

As for getting a fix under canopy, I haven't really tried this much but my GPS-V does have trouble holding it's lock under dense cover. The only way to know how good or bad a unit is would be to test them side by side.

It does help if you get a lock on all available sats before you enter the difficult area. If you cold start your GPS while under canopy you probably won't get a lock at all.

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