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From: John De Armond
Subject: Re: GPS
Date: Sat, 11 Dec 1999 14:02:43 EST

DougB wrote:
> They all basically do the same thing...some with more bells and
> highway maps and such. The difference I'd look for is ease
> of use. I have a Garmin II plus, which is a great basic unit that's very
> easy to use. Marks waypoints; maps a trail; etc.
> Doug

Err, ah, well now the rest of the story :-)  While they all read the
satellites and compute positions, some do it a lot better than
others.  Other factors are also a consideration.  Most of the
current production of all brands use the Rockwell receiver chipset
so the basic functionality is the same.  However antenna design has
a huge influence on how the receiver performs.  I have an older
Trimble EnsignGPS, a Magellan GPS2000 and a Garmin GPSIII+.  THe
difference in performance is remarkable.

The Trimble takes an average of 15 minutes to acquire satellites
even when the almanac is up to date.  It eats batteries at the rate
of a set every 4 hours.  The Magellan, a basic unit, acquires a fix
when in the clear in about 30 seconds.  Batteries last 24 hours. 
The GPSIII+ acquires about as fast but eats batteries in 4 hours. 
These are the first two major differences and probably the most
important for everyday use.  If the receiver takes forever to
acquire an initial fix, you'll find yourself not using it much.  Or
else leaving it on all the time and eating batteries (or paying
extra for a 12 volt adapter.)

The means of external power is the next issue.  The Trimble requires
a separate adapter that replaces the battery.  Ditto the Magellan. 
The GPSIII+ requires only a simple cable.

For use in a vehicle, the ease of adapting an external antenna is
paramount.  My unit works without an external antenna in my Itasca
because its cab is fiberglass.  However the unit is pretty worthless
in my cars because of the shielding the metal body provides.  The
Trimble and Magellan require external antenna couplers that slip
over the end of the unit.  The GPSII+ has its antenna attached by
means of a BNC jack.  They sell an external antenna but I've found
that a short BNC jumper cable between the antenna that came with it
and the unit works fine.

The Trimble and GPSII+ have the ability to do fix averaging.  This
averages the results of several fixes.  It is very useful for slow
motion/stopped use because it averages out a lot of the error caused
by Selective Availability.  It does that at the expense of slower
updates and a limitation on speed.  If you're using the GPS unit to
navigate while hiking or bike riding, this is a vital feature.

I don't use a computer with mine so I can't give first-hand
experience about that.  I do know that at least one company makes a
little hocky-puck receiver without display designed only to
interface to a computer.  The hocky-puck goes on the roof of your
vehicle.  they even have a version for the Palm Pilot.  About $100.

Check out  Literally more than you'd ever
want to know about GPS receivers.  You'll spend days at this site!

Also check out, the Purple Open Project.  This is
a very interesting fellow.  He's trying to bring the concept of
shareware to hardware.  he's manufacturing a data interface cable
for the Garmins in his basement.  You drop him a note and he sends
you a connector.  If you like it, you send him whatever money you
think it's worth.  If not, no obligation.

Final note:  My GPS receiver has become as important to me as my
wallet.  I'd not leave home without it.  Of particular interest to
leisure travelers is how nice it makes it to find your way back to
your campground (or, ugh, motel) after you've explored a new area. 
Fancy mapping capabilities are not necessary.  Nothing more than a
fix of the destination and a little intuition about how the road run
is all that is needed.  I store the fixes of all my favorite
out-of-town restaurants and other attractions so that when I'm
passing through again, all I have to do is set a course to that
destination to find it.  No need to rely on my increasingly missing
memory :-)


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