My neu-S4: a one-year review

[Brett Dikeman]

At 7:41 PM -0800 11/20/01, Ti Kan wrote:

>Would be nice if the initial startup of the navigation system is faster.

This is inherent to GPS...not the car's fault, unless the GPS unit
doesn't preserve its internal clock.

GPS relies on a highly accurate clock to figure out how far it is
from each satellite; that clock needs to be set somehow, and the
trick is this...how do you set a clock that needs to be accurate
enough to time distances between you+satellite, when you have no idea
how far you are from the satellite you're picking up?

Classic chicken/egg problem.  The solution is that you need to find
more than one satellite, but that can take a little time.  So Garmin
and most other GPS unit manufacturers store the clock data unless the
batteries go dead.  This results in a turn-on time of around 45
seconds or less if you've got great visibility.  If the battery goes
dead, or the unit's position changes more than X amount(pretty big, I
think it's around a couple thousand miles) while it is turned off, it
can take the little guy quite a while to figure out where the heck it
is.

The delorme tripmate gets a big "F" in my book for this reason(it
doesn't have the capability to store the clock, bah!) and a whole
host of others(like, say, really poor reception and accuracy?
Incompatibility with most programs?  Hmm :-)

B
PS:for the interested, a recent DIY-satellite launched by a HAM radio
group(I think?) used GPS to successfully locate itself in outer
space. It was, by all counts, a first...everybody said "sure, it'll
work!" but everyone also held their breath to see :-)  If I remember
correctly, it worked really well; combined with selective
availability being off these days and the lack of a nasty 'ol
atmosphere slow down randomly the radio signal, positioning info was
great.  This satellite, btw, was one that used a metal tape measure
for communications instead of a $50k antenna deployment system.
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