SPOT messenger

On May 14, 11:34*pm, Darryl Ramm wrote:
On May 14, 4:37 pm, "Matt Herron Jr." wrote:

The SPOT does not "wait for an opening" to talk to Globalstar, it has
no idea where the Globalstar satelites are, it just sends blind, then
retransmits the same message later. It's pure simplex, there is no
"carrier detect", no handshake, no ACK. Nothing. *The Globalstar
satellites are just dumb one-way bent pipe repeaters. Sometime being
simple is a beautiful thing.

I always assumed the 20 minute thing was put into the SPOT system
because sat time is expensive.

Executive summary: go buy yourself a SPOT messenger!

I did and I love it! I'm just waiting for them to create a public side
to findmespot.com so I can share my tracks. Right now you have to give
out the admin password to your account (which includes your credit
card on file, etc) for people to see your tracks.

-Robert

Robert M. Gary wrote:

I did and I love it! I'm just waiting for them to create a public side
to findmespot.com so I can share my tracks. Right now you have to give
out the admin password to your account (which includes your credit
card on file, etc) for people to see your tracks.

They've done that already, and it works well. Take another look at the
site to see how you can create public pages.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On May 15, 9:05*am, Eric Greenwell wrote:
Robert M. Gary wrote:
I did and I love it! I'm just waiting for them to create a public side
to findmespot.com so I can share my tracks. Right now you have to give
out the admin password to your account (which includes your credit
card on file, etc) for people to see your tracks.

They've done that already, and it works well. Take another look at the
site to see how you can create public pages.

Thanks to all for posting. I'm gathering responses to several posts
here. First, on the sharing option, they say it's a beta and in my
experience (and that of three people who tried it on various
computers) it does not work. While it may work some of the time,
that's not good enough for the S&R application, so I've had to share
my account password with my backup people.

Second on Eric's post re zipper on top vs. the bottom (#13 in this
thread), I emailed Allen Silver and, not surprisingly, there is a
logic to the zipper location. Here's his response:

"There actually is a reason why I mounted it on the bottom. One is to
protect it from getting snagged and accidentally opened and the other
is about gravity. If you left the snap that secures the zipper to the
pack undone and you had to bailout the zipper could unzip during the g
forces of opening. Not likely to occur, but you know about Murphy's
Law."

Thanks for the posts on vertical vs. horizontal. I'll have to try it
in the SMAK PAK and see what happens.

Martin
WT

On May 15, 8:19 am, "Robert M. Gary" wrote:
On May 14, 11:34 pm, Darryl Ramm wrote:

On May 14, 4:37 pm, "Matt Herron Jr." wrote:
The SPOT does not "wait for an opening" to talk to Globalstar, it has
no idea where the Globalstar satelites are, it just sends blind, then
retransmits the same message later. It's pure simplex, there is no
"carrier detect", no handshake, no ACK. Nothing. The Globalstar
satellites are just dumb one-way bent pipe repeaters. Sometime being
simple is a beautiful thing.

I always assumed the 20 minute thing was put into the SPOT system
because sat time is expensive.

I've got to be believe the 20 mins is a wild design guess on their
part. The practical transmit reliability with SPOT across their
intended users has got to be dominated by environmental factors,
device antenna direction, obstructions (trees, mountains, etc. for
hikers, car roofs) and finally satellite position. Modeling the number
and durations between retransmit attempts to deal with these factors
would be very difficult. You'd start with a simplified model that just
factored satellite coverage and message collision probabilities and
guess from there. You want to cap retransmits to reduce battery
consumption and just excess further collisions. For 911 it keeps
retransmitting much longer AFAIK. And the only "cost" for the sat time
is the risk of further message collisions.

Darryl

Darryl Ramm wrote:

And to Martin's earlier comment, OK etc. does not always take 20
minutes to send, it might take up to that (or may never successfully
send) but you can see that messages often go out quicker than this.
I'm missing the point of the argument used, I use tracking becasue it
is convenient and I don't want to press buttons, not because I think a
track position report is more likely to get out than an OK report.

I also use tracking for these reasons. I do think an OK messages will
get out more reliably a tracking message, because OK messages have a 20
minute window to get out, versus the 10 minute window of the tracking
messages. All my OK messages have been sent, but an ocasional tracking
message isn't, sometimes two in a row.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

snip
I had thought I might use it in OK mode to report my position more
frequently than the every 10 minutes in "track mode." At 120 kts,
that's every 20 nm, leaving as much as 1500 sq miles to search. Better
than those looking for Steve Fosset had, but still a lot. Of course,
the average will be less than 1500 sq miles. There is a 50% chance it
will be less than 400 sq miles.

snip

Of course this assumes that the Spot does not survive the crash or can
not transmit after the crash. If it is still operable after the crash
then whit in 10 minutes It will report the your exact location.

Brian