[pct-l] About my first generation SPOT

[Dan Jacobs]

On Oct 18, 2012 8:33 PM, "Kathi" <pogo at pctwalker.com> wrote:
>
> It was my understanding that the SPOT units do know if the message
> reached the satellite. Normally when I was testing it and was in poor
> view of the satellites (between buildings, in my house, etc.) I would
> get any error message that the satellites were not visible.

The SPOT device uses two different satellite systems: GPS and
Globalstar. The device seeing one system does not mean it can use
both. The SPOT device is a one way communicator: it transmits a very
short message at very low power "in the blind", meaning it transmits
the same message more than once so that there is a greater chance of
the message being received by the satellite. It may still be able to
successfully transmit its message even without GPS lock, but it cannot
send a message without a Globalstar satellite receiving it even with
excellent GPS reception.

According to their manual that I found online, the SPOT unit continues
to send messages other than 911 for up to 20 minutes, and their
network tosses out any after the first received attempt
(http://findmespot.com/en/downloads/SPOT_UsersGuide_2007_10_16.pdf).
If it was a true two way system where the device was told the message
was received  there would be no need to continue to transmit for
twenty minutes and for their system at their data center to toss out
all of the other received duplicates. If the unit could be told that
the message was received and to stop sending it, users could have
their batteries last longer.

Their manual also repeats something kind of vague at least twice that
I found skimming through it: "That’s why the SPOT Messenger is
scheduled to automatically send multiple messages in every mode –
giving you excellent overall reliability" and "It’s normal for some
messages to be blocked by your environment. Therefore, SPOT
automatically sends repeat messages, resulting in excellent overall
reliability." This says to me that the unit sends messages over and
over in the hopes that just one gets through.

I'm not putting the SPOT device down. I want one, I can't afford one
right now. I would like my family and friends to have the ability to
see where I am, what I might be doing. I just won't depend on it to
save my life. It might help, but I won't put that much trust in any
one piece of technology.

SPOT is useful, has clearly been shown to be useful, but has also been
shown to not be as reliable as some folks might have thought.

Dan Jacobs
Washougal