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Old 11-08-2007, 04:54 PM   #7
TomW
Beastly Adventurer
 
Joined: Jan 2006
Location: Ft. Payne, AL
Oddometer: 1,013
Quote:
Originally Posted by offroute
...I'm finding that the unit definitely needs a reasonably clear view of the southern horizon to get its message out... With a clear view the messages are delivered promptly. However, my concern is crashing alone in a heavily timbered or easy-west facing canyon and not being able to walk the unit up so it can communicate with the GS satellite....
Hmmm...I read their material and although they never say so, Spot does not use geostationary satellites. They use a constellation of some 40 satellites in low earth orbit, thus they can be anywhere above the horizon -- not just in the southern sky. Spot is owned by Globalstar, operator of the somewhat popular consumer sat phone system, so I'm sure they use the same satellites (the coverage map on Spot's website is the same map Globalstar uses).

Regarding reliability of uplink sat comms, here's an excerpt from Globalstar's web site:

"...Technology / Path Diversity
Path Diversity is a patented method of signal reception that permits the combining of multiple signals of varying power strengths into a single, coherent signal. Subscriber terminals [i.e., Spot units] will be able to operate with a single satellite in view, though typically two to four satellites will be overhead."

So, that's good news for a rider down in an east-west canyon (a view of the southern sky is not required); however, since a line-of-sight path to the satellite is still required, a canyon will reduce the time a satellite is in view as it passes overhead. (That window of time may not correspond with the Spot unit's once-every-5-minute transmit schedule.) Logic dictates that sooner or later a satellite will be in view when the unit transmits, but the narrower the canyon, the longer that wait might be. Hey, nothing's perfect, and at a cost that's a fraction of a PLB (which has the same technical limitation re: line of sight path to the satellite), Spot sounds pretty attractive to me.

It would be more attractive if it had an external power jack (with the internal battery for backup) and provision for external antennae (so it could be kept in a secure location when used for tracking).

I'm interested to hear your real-world findings as I'm thinking about getting one myself.

Cheers.
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TomW
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