SPOT tracking for 2009 contests?

On Feb 13, 10:30*am, flying_monkey wrote:
On Feb 13, 1:04*pm, Tuno wrote:

I'll be doing an experiment early next week with a cross-country
drive, with the SPOT positioned to have a good view of the sky, and
see what kind of tracking success rate is achieved.

I drove from Philly to Memphis over 2 days with the spot laying on the
dash, and I don't think it missed more than a half dozen reports. *I
also carried it while towing in a Pawnee and got no reports. *??

Ed

Ed

I suspect a common cause of “no reports” is people accidentally having
the SPOT messenger send a single “OK” message instead of putting the
unit in SPOTcast/tracking mode. Done it myself when in a hurry. That
one OK message may or may not get through (even with it's automatic
retransmission). The SPOT Messenger’s user interface with overloading
of button functions is very poorly designed. Hey it's not like
anybody's life might depend on the thing being easy to use...

Another problem may be the SPOT Messenger was in the correct mode but
never received a GPS fix. Check those LEDs are blinking in unison, not
alternately. Was the SPOT messenger close to another GPS receiver/
antenna? Although it is unlikely the local oscillators may interfere.
Without a GPS fix no SPOTcast/tracking reports will be sent, same as
for "OK" messages. BTW "Help" and "911" messages will be sent without
the GPS position if the SPOT messenger could not get one.


Darryl

On Feb 13, 10:04*am, Tuno wrote:
Mike is referring to my flight, but being the moron that I am, I had
the SPOT on my chest strap where its satellite exposure was much more
limited than it should have been, and I spent a lot more time
thermaling in the last two hours than the first two.

I'll be doing an experiment early next week with a cross-country
drive, with the SPOT positioned to have a good view of the sky, and
see what kind of tracking success rate is achieved.

2NO


Mike, Ted

Ted thanks for your clarification, I was just going to ask where the
SPOT messenger was mounted...

I was one of the earliest SPOT messenger users in sailplanes and have
been impressed by them in tracking and watched their adoption in
soaring. So while not defending SPOT or Globlalstar I'm do get curios
about reports of reliability problems. I'm also starting to see claims
of "service degrading" (like Mike's claim) and wonder how those claims
are established based on limited sample over limited time. I am not
defending SPOT but I am worried about anecdotal reports or problems
getting attention and as the population of users increases it is
inevitable that people will complain publicly about problems. If
other users pile on adding that they have seen problems it then can
appear to have some rapidly increasing rate of problems. So lets be
careful about making claims of problems, and especially of
degradation of service.

One of my concerns is possible obstruction of the SPOT messenger’s
view of the Gloabalstar satellites that I notice when many pilots are
using them, especially when work on parachute harnesses (just like Ted
did).

In practice with my SPOT messenger mounted on the canopy rail on my
ASH-26E or on the top of the instrument panel of a Duo Discus etc.
and away from any other GPS receivers and with no obvious obstructions
to vast areas of the sky I find that the system is dropping maybe a
few percent of messages. Almost always just single message drop. If
other users want to report bad experiences with SPOT messengers then
*please* help make the comments meaningful by saying where the units
are mounted and in what type of glider or aircraft and whether you
were doing things like flying against a mountainside or down in a
steep valley etc.

SPOT makes claims like in the continental United States of a 99%
reliability for sending a single message in 20 minutes (when there are
three attempts made). I suspect that probability does not apply to an
individual SPOTcast/tracking position since it only sends every ten
minutes and does not retransmit the message unlike with other
messages. SPOT has not made any claims about the reliability of
individual SPOTcast/tracking messages. Globalstar claims simplex
message reliability exceeding 99% but this is a little hard to decode
since I suspect this also assumes automatic message retransmission not
used by SPOTcast/tracking.

Some pseudo-technical hand waving might help. SPOT relies on GPS and
the Globlalstar satellites. There are 40 or so Globlalstar satellites
are in LEO at an altitude of about 1,300 km, and 30 or so GPS
satellites in a considerably higher MEO at around 20,000 km altitude.
(approx AGL altitudes not orbital radius). Globalstar satellites have
a 114 minute orbital period compared to about 12 hours for a GPS
satellite.

The GPS satellites just transmit a signal the GPS receiver picks up.
The Globalstar satellite are not only ripping by faster they also have
a more challenging signal path and have to redirect the uplink signals
down to ground stations (aka gateways) (it's just a bent pipe, the
satellite are very dumb, there is no store and forward or satellite to
satellite communions in Globlalstar, say unlike Iridium).

The SPOT messenger just transmits blind, it has no way of knowing
where the satellites are or if a message is ever received by them. The
Satellites just redirect the signal down to the ground stations. Since
there may be (are often) multiple satellites in view Globalstar
deduplicates any signals on the ground that came through different
satellite paths.

In ten minutes a single Globalstar satellite transits about a 30
degree orbital arc. For somebody near the surface of the earth the
satellite will ltransit more than 30 degrees of their usable field of
view every 10 minutes. Globalstar talks about single satellite
“connect” times of 10 or so minutes. So hopefully people get the idea
how quickly these things are moving overhead and how the a SPOT
messenger may be relying on a satellite off in one direction to send
one SPOTcast/tracking position report and ten minutes later be relying
on one in a different direction in the sky. Sometimes the message will
go via multiple satellites, sometimes not. Sometimes things nearby
might obstruct the critical satellite, sometimes not, sometime the
glider banked in a thermal will be enough, and so on. Losing some
number of individual SPOTcast tracking messages should be expected
(i.e. definitely don't assume you should get "99% message reliability"
in practice with SPOTcast/tracking).

The best place to put the SPOT messenger is somewhere where the unit
is level to the horizon had the sky view is not obstructed. The planar/
strip line antennas used into these sorts of devices have a remarkably
wide field of view. While -3dB beam width might be something like +/-
30 degrees either side of vertical the signal strength fall off
relatively slowly and the usable angle is likely much wider (and I
suspect SPOT/Globalstar relies on much wider angles).

Wearing the spot messenger on your parachute harness is a common
thing. This may be a great tradeoff if the pilot wants the SPOT
messenger to go with him in a bailout but it may not be good for
reliable satellite reception – but that’s is a choice the pilot should
make. If worn on the front of the harness this may be going to tilt
the SPOT messenger forward at an angle, obscuring part of the sky
behind the pilot, or if sitting on top of the shoulder a large part
of the sky is going to be obscured by the pilot’s head and portions of
the fuselage behind the pilot’s seat.

---

The following advice/comments on using SPOT may be helpful. This is
based on my read instruction manuals and other documentation. Please
speak up if anything looks wrong.

Check the SPOT messenger is receiving GPS - if the two Leeds are
blinking in unison then the SPOT has a GPS fix, or did last time it
looked at the GPS (every 5 minutes or so I believe). If the LEDs are
blinking alternately the SPOT Messenger does not have a GPS fix.

Don't place the SPOT close to another GPS receiver/antenna; there can
be interference between local oscillators. This is not just specific
to SPOT. If you do this then at least make sure that the SPOT LEDs
show it is getting a GPS fix.

Look out for RF opaque areas like carbon fiber fuselage, metal cockpit
frames, etc. may obstruct the signals. The pilot's fat, RF opaque,
head might be a significant factor if the SPOT Messenger is mounted on
their shoulder.

---

Some other things worth knowing about SPOT are the different
retransmission behaviors of the unit...

SPOTcast/tracking messages are sent once every 10 mixtures. There is
no retransmission of an individual message, you just get a new
position message sent 10 minutes later. If the SPOT GPS cannot get a
fix no message is sent.

An "OK" message is retransmitted three times, with about 5-10 minutes
apart (so SPOT says to wait about 20 minutes for all three messages to
go out) each message contains the same position data from when you
pressed OK and is deduplicated by the system so users only see one
message. If the SPOT GPS cannot get a fix no message is sent.

A "Help" message is retransmitted about every 5 minutes for one hour.
A new GPS coordinate is sent with each report. If the SPOT GPS cannot
get a fix a message is sent with no position information, at least
that let people know you are asking for help.

A "911" messages is retransmitted about every 5 minutes until the
batteries run flat. A new GPS coordinate is sent with each report. If
the SPOT GPS cannot get a fix a message is sent with no position
information, at least that let people know you are asking for help.

So one take away is pilots should definitely know to use “Help” (or
“911”) if they need assistance and make sure you have agreed on what
exactly a “help” message means (I’d suggest putting “need retrieve” or
whatever in the email generated).

---

BTW A few "degradation" rumors I’ve heard were fueled by confusion
with problems with Globlalstar sat phone voice services. The
Globlalstar satellites amplifiers used by the S-Band downlink for
voice data to handsets degraded in space and have severely affected
this service. This has been a major black-eye for Globalstar , is well
known and has been publically documented for years. The L-Band uplink
to the satellite is not affected by this. SPOT uses just the L-Band
system. Globlalstar are going to be launching a new satellite
constellation (starting this year) that will fix the S-Band problems,
that constellation will be compatible with current L-Band devices like
SPOT.

Again, SPOT messengers are wonderful devices, and I encourage pilots
to use them, just take a little time to make sure you are using them
as best as possible. Finally while I am a fan of SPOT, especially when
used for tracking, I also like redundancy and independence of carrying
a 406 MHz PLB (with GPS) on my parachute harness in case things really
go bad.

Hope this helps a little.

Cheers



Darryl

I've done tests while hiking and riding my mountain bike too and find
if it's not horizontal, the number of missed locations increases.

In my glider, I attach mine to my parachute harness too. I reckon
that if I have to bail out there's no sense having my rescue device in
the wreckage rather than with me! With my supine position in the
Discus, this puts the unit in about a 45 degree position. Not
perfect, but usually OK. Another ASA pilot has done some tests with
it mounted horizontally behind his head rest and even he has found
quite a few dropouts lately. He attributes this to a lot of circling
in weak winter conditions.

We'll be testing and reporting back some more.

Mike

On Feb 13, 3:11*pm, Mike the Strike wrote:
I've done tests while hiking and riding my mountain bike too and find
if it's not horizontal, the number of missed locations increases.

In my glider, I attach mine to my parachute harness too. *I reckon
that if I have to bail out there's no sense having my rescue device in
the wreckage rather than with me! *With my supine position in the
Discus, this puts the unit in about a 45 degree position. *Not
perfect, but usually OK. *Another ASA pilot has done some tests with
it mounted horizontally behind his head rest and even he has found
quite a few dropouts lately. *He attributes this to a lot of circling
in weak winter conditions.

We'll be testing and reporting back some more.

Mike

Just one quick comment about placing the SPOT Messenger behind the
pilots head. This can be a great location but I've noticed some pilots
just sitting the SPOT Messenger behind them on the luggage shelf.
Sometimes on top of stuff there, sometimes just on the shelf. In
either case the pilot's head, metal canopy locking mechanism and
carbon fibre spar elements, might provide significant signal
obstructions, or the SPOT Messenger may just shift in flight. If I was
going to put one back there I'd make up a mount that held the unit up
against the top of the inside of the turtledeck area. Obviously after
making sure sure that the turtle deck itself is RF transparent, even
with carbon fuselages some manufacturers use just glass or kevlar in
that area.

I like my SPOT mounted on the canopy rail (fastened on with 3M Dual-
Lock tape) since I can can lift the unit off and check I have it in
the correct mode and it is getting GPS fixes etc. I wish SPOT had a
dash mount unit with buttons and LEDs on one edge.

Darryl

Just a couple of notes here from my extensive use of the SPOT
messenger. I have driven on several cross country trips with the
tracker on, as well as flown my Cessna 120 with it up in the dash
board above the panel in both the truck and the plane. In both cases
I had no problems with reporting or tracking. There were maybe two or
three "Reports" that came a bit late in all of my trips.

OK City to Albuquerque (Driving)

OK City to Indianapolis to Hershey, PA. (Driving)

OK City to Indianapolis (Flying)

I did, however have trouble in the glider in Parawon this summer with
the SPOT missing reports. My uneducated guess says that this was due
to the fact that there is a lot of turning in gliders as well as the
fact that I left it clipped to the parachute, and it's view of the sky
was less than optimal. I don't know if my experiences are of any help
in figuring out what's going on, but "them's the facts".

One of the huge problems I see for contests this summer is that the
SPOT used to erase the tracks every day to day and a half. Sometime
this fall, they started going to leaving the markers up for seven
days, with no way to display any less than the last seven days worth
of SPOT's on the shared page. This makes things very confusing when
you have more than one or two days worth of SPOT's up on the map.
(Especially in a contest environment)

On a completely different side note, I DO know that when the SPOT is
put onto the dashboard of an E-3 AWACS (707 airframe) it will track a
flight just fine, however the dots will be REALLY far apart.

P.S. I just tried it at my current "Deployed" location with the
military. Seems to work fine here!

http://share.findmespot.com/shared/f...W2PuiViqCs Zg

One of the huge problems I see for contests this summer is that the
SPOT used to erase the tracks every day to day and a half. *Sometime
this fall, they started going to leaving the markers up for seven
days, with no way to display any less than the last seven days worth
of SPOT's on the shared page. *This makes things very confusing when
you have more than one or two days worth of SPOT's up on the map.
(Especially in a contest environment)

Mitch,

The glidingmaps.com software doesn't use the shared SPOT web page. It
uses the XML feed that the shared SPOT pages use, allowing web page
developers to do what they want with the reports. Thus the 7-day
window is not an issue.

2NO

On Feb 13, 4:55*pm, Mitch wrote:
P.S. *I just tried it at my current "Deployed" location with the
military. *Seems to work fine here!

http://share.findmespot.com/shared/f...glId=06Fz4iX5x....

Don't get lost in the swimming pool.

Darryl

Seems like a very nice place to be deployed. Are you indeed in the
spot it shows you.

ASW27BV

On Feb 13, 10:00*pm, wrote:
Seems like a very nice place to be deployed. *Are you indeed in the
spot it shows you.

ASW27BV

You bet! The "War on drugs" must be fought! And who better to find
the dope runners than a plane with a big frisbee on top?