My first suggestion is to check out sci.geo.satellite-nav. It's a very
active newsgroup concerning gps and dgps with a high technical to noise
ratio. Also chek out http://vancouver-webpages.com/pub/peter/index.html
I suggest buying a portable 12 channel parallel receiver rather than the
Tripmate. I own a Garmin GPS II+ which I'm very happy with.
1. Parallel receivers process the signals from up to 12 satelites at once.
Acquisition time is reduced in parallel receivers. I don't think
that the Tripmate is a true parallel receiver.
2. The prallel receivers have more 'sensitivity' compared to the
sequential receivers due to processing gain.
3. Portable receivers use less power than the Tripmate. My Garmin runs on
4 AA's for over 24 hours. It has a internal switching power supply
(more efficient than linear) which can accomidate a wide voltage range
(I think 8-30 volts).
4. You can use a portable unit stand-alone! Most portable units have a
serial RS232 level output like the Tripmate as well.
5. I built a few data/power cables for my Garmin II+ for only a few bucks.
The connector can be had practically for free
http://pfranc.com/projects/g45cntr/beans.htm
6. For impaired receiving conditions (i.e. forest canopy) you can attach
an amplified antenna to portable units (Lowe makes one for ~$65).
7. If you live within 150 miles from the coast or major inland waterway,
you can use the US Cost Guard's DGPS signals
http://www.navcen.uscg.mil. Homebrew DGPS receiver project at
http://home.san.rr.com/bix
#---------------------------------------------------------------------------
# Geoff Parker 
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