Wed 7/15 fantastic day, but SPOT??

I soared from the Minden area down to abeam Independence then back to
Mono Lake before needing my engine to get home to the Bay Area. (I
also used the engine to get me to Minden.) As long as I stayed with
the clouds, lift was fantastic east of the Sierras. I saw 13 kts on my
averager several times, and 10 knots while dolphin flying. South of
Mono Lake, there were clouds that could take you to the Whites or the
Sierras and, since I'm a sucker for soaring the Sierras, I took that
fork in the clouds. Made it to abeam Independence before turning
around. Lift on the Sierras was spottier -- as usual, but still very
good.

When I got home and checked my SPOT messenger track was missing an
hour and twenty minutes -- a new record. The last message before the
dropout was at 12:10 PM PDT and the next one was around 1:30 PM. Did
anyone else with a SPOT have a similar problem today? If anyone wants
to compare data, my shared page is

http://share.findmespot.com/shared/f...QTLgQBTp7N ax

but, as usual, it will disappear in a few days or a week.

Thanks for any help on this question.

Martin

Martin,

I've had several flights with that long of a gap in the tracking
messages. No one has come up with a good explanation.

Is your flight on OLC ... ? Thirteen knots, you gotta share that!

ted/2NO

Martin:

I did a serious investigation on the problem involving some
experiments and analysis and I made a presentation to my local club.
My presentation is available for download from my Wing Rigger website:
www.wingrigger.com. (click Extra Soaring Content in lower right
corner).

Here is the bottom line: the radio link between Spot and the Global
Star network is a bit fussy. There are some 40 Global Star satellites
in low earth orbit. Statistically 2 or 3 satellites are likely to be
in view but sometimes just one. When you consider the geometry of
the low earth orbit and the statistical distribution of the satellites
it will almost always be the case that the satellites are very near to
the horizon. So what matters is that Spot has a line of site view to
the horizon. Since you don’t know exactly where on the horizon the
Global Star will be, the only sure thing is to have a clear view of
the entire horizon. This is often rather difficult. My experiments
proved that when you do have a 360 degree view of the horizon Spot
works perfectly. So part of the answer relates to the mounting
location in your glider. What I found works best is a location
behind my headrest high against the underside of the canopy. I have a
picture of this mounting in the mentioned presentation.

There is more to the story. Even with optimal mounting you will miss
some Spot transmissions because gliders spend a portion of their time
in banked turns. When the glider is banked, a certain percentage of
the horizon becomes blocked by the glider’s wings, fuselage etc. If
there aren’t any satellites in the unblocked portion of the horizon,
your message won’t get out. I studied this effect by carefully time
correlating the exact times at which Spot succeeded or failed in its
transmissions to the time stamped record created by an IGC file that I
examined in See You. I did this for two long flights. With my
“optimal mounting” I miss about 20% of transmissions while banked and
I miss only 2% when in substantially level flight. So my Spot
tracking performance is pretty good, but certainly not perfect.

One other consideration relates to the performance of the patch
antenna that is used in the Spot device. The antenna preferentially
transmits to one hemisphere. So the unit works best when the unit is
mounted flat – label side up. Any other mounting angle reduces your
chance of linking to a satellite on the horizon. I’m sure this also
comes into play when the glider is in a banked turn.

Steve Koerner (GW)

PS:

Martin:

Here is a link to my Spot log for a long flight I made in AZ/UT the
day before yours: www.tinyurl.com/4fuc2h
I missed only one transmission in eight hours on that flight. That's
better than I would have expected. Since it was a high altitude
flight, I'm thinking that might have helped the odds of seeing more
horizon distance.

PPS:

Tuno: Were you sleeping during my lecture?

Steve

On Jul 16, 6:04*am, Tuno wrote:
Is your flight on OLC ... ? Thirteen knots, you gotta share that!

Alas, I've been unable to read the files from my Colibri data logger
since I upgraded my PC's OS -- the Colibri uses a serial port and
either my serial-USB adapter doesn't work since that upgrade or the
Colibri itself is broken. I've seen 11 kts before on the averager, but
I am pretty sure 13 is a new record for mine, especially in 3 or 4
thermals in the same flight. Once I took the fork to the Sierras, the
lift was nowhere as good -- though that was partly expected. I was
willing to sacrifice thermal strength (and maybe even having to turn
on the engine) for the fantastic views the Sierras offer compared to
the more barren ranges to the east. Meadows, lakes, glacial remnants
make for great sightseeing, but do cut into thermals. Coming home to
the Bay Area was a bit problematic in that the clouds made an arc far
to the east before I could cross the Sierras, so I had to turn on the
engine for about 10 minutes near Mammoth Lakes to gain enough altitude
to safely cross as a glider at Yosemite. But I'd kinda expected that
since the BLIPMAP showed that would be the case at 5 PM local time.
Even so, I had a 6.6 hour flight with only 1.0 engine time.

Sorry not to be able to post the track, but an earlier one-day trip is
described (including a SeeYou map, showing engine use) at
http://tinyurl.com/5ahbcm

Martin

PS The ship is for sale. I'll miss it, but a project is taking too
much time and passion that used to go in here. If interested,
http://tinyurl.com/56qseu has a description of that project -- and
even connects it to soaring.

On Jul 16, 7:48*am, Steve Koerner wrote:
I did a serious investigation on the problem involving some
experiments and analysis and I made a presentation to my local club.
My presentation is available for download from my Wing Rigger website:www..wingrigger.com. *(click Extra Soaring Content in lower right
corner).

Steve,

Thanks for that detailed analysis of SPOT behavior. While it helps in
understanding SPOT generally, my question -- and big concern -- is why
that flight was different from all other flights. I don't believe I've
never had more than a 30 minute gap (2 missed transmissions) before,
yet this time the gap was 90 minutes (8 missed transmissions). I was
asking if anyone else had a track from that specific day and time (JUL
15, 1900-2020 Z) and general location (roughly from Oakland, CA to
Lake Tahoe). If so, I wanted to know if they had coverage or also had
around a 90 minute hole in their data.

Martin

On Jul 17, 9:08*pm, Hellman wrote:
On Jul 16, 7:48*am, Steve Koerner wrote:

I did a serious investigation on the problem involving some
experiments and analysis and I made a presentation to my local club.
My presentation is available for download from my Wing Rigger website:www.wingrigger.com. *(click Extra Soaring Content in lower right
corner).

Steve,

Thanks for that detailed analysis of SPOT behavior. While it helps in
understanding SPOT generally, my question -- and big concern -- is why
that flight was different from all other flights. I don't believe I've
never had more than a 30 minute gap (2 missed transmissions) before,
yet this time the gap was 90 minutes (8 missed transmissions). I was
asking if anyone else had a track from that specific day and time (JUL
15, 1900-2020 Z) and general location (roughly from Oakland, CA to
Lake Tahoe). If so, I wanted to know if they had coverage or also had
around a 90 minute hole in their data.

Martin

Martin

You want to end the guessing game and tell us where your SPOT
messenger is mounted? On your harness? On your shoulder? Obstructed
by your head? What is the effective field of view of the antenna?

You were tracking roughly the same heading for all that time. And
that heading (very) roughly lines up with one of the inclined planes
of the GlobalStar constellation.

The GlobalStar satelites orbit in a interweaved pattern with two
inclined planes at +/- 80 degrees or so (you can see a simulation here
http://www.youtube.com/watch?v=G8VPEueequM or you can actually play
with the SaVi software shown in the video, see http://savi.sourceforge.net)..
It is quite possible that things happen like the satelites flying from
the south west to north east are obscured over your left shoudler if
say your SPOT messenger was to the right side of your head and all
those passes could be obscured and maye the next parallel path to the
east is too far away. That leaves the satellites tracking north-west
to south-east and just maybe again if your head partially obscured
those then the satellite does not see the spot until it is further
overhead and out of the optimal bent-pipe geometry to reach the
Alberta, Canada ground station. So maybe in the whole time you just
get maybe one shot when the SPOT fires off its track message where it
manages to see a satellite to get it a bent path to the Texas ground
station. Maybe you just managed to get things timed so bad that you
never happened to have a satellite with bent-pipe view to any ground
station when your SPOT happened to fire the TRACK message.

This is all very uninteresting if the SPOT messenger is mounted say on
your parachute harness and inclined or significantly obscured. Tell me
it is out flat in the open and I'll actually care.

Darryl

On Jul 17, 10:34*pm, Darryl Ramm wrote:
On Jul 17, 9:08*pm, Hellman wrote:





On Jul 16, 7:48*am, Steve Koerner wrote:

I did a serious investigation on the problem involving some
experiments and analysis and I made a presentation to my local club.
My presentation is available for download from my Wing Rigger website:www.wingrigger.com. *(click Extra Soaring Content in lower right
corner).

Steve,

Thanks for that detailed analysis of SPOT behavior. While it helps in
understanding SPOT generally, my question -- and big concern -- is why
that flight was different from all other flights. I don't believe I've
never had more than a 30 minute gap (2 missed transmissions) before,
yet this time the gap was 90 minutes (8 missed transmissions). I was
asking if anyone else had a track from that specific day and time (JUL
15, 1900-2020 Z) and general location (roughly from Oakland, CA to
Lake Tahoe). If so, I wanted to know if they had coverage or also had
around a 90 minute hole in their data.

Martin

Martin

You want to end the guessing game and tell us where your SPOT
messenger is mounted? *On your harness? On your shoulder? Obstructed
by your head? What is the effective field of view of the antenna?

You were tracking roughly the same heading for all that time. *And
that heading (very) roughly lines up with one of the inclined planes
of the GlobalStar constellation.

The GlobalStar satelites orbit in a interweaved pattern with two
inclined planes at +/- 80 degrees or so (you can see a simulation herehttp://www.youtube.com/watch?v=G8VPEueequMor you can actually play
with the SaVi software shown in the video, seehttp://savi.sourceforge.net).
It is quite possible that things happen like the satelites flying from
the south west to north east are obscured over your left shoudler if
say your SPOT messenger was to the right side of your head and all
those passes could be obscured and maye the next parallel path to the
east is too far away. That leaves the satellites tracking north-west
to south-east and just maybe again if your head partially obscured
those then the satellite does not see the spot until it is further
overhead and out of the optimal bent-pipe geometry to reach the
Alberta, Canada ground station. So maybe in the whole time you just
get maybe one shot when the SPOT fires off its track message where it
manages to see a satellite to get it a bent path to the Texas ground
station. Maybe you just managed to get things timed so bad that you
never happened to have a satellite with bent-pipe view to any ground
station when your SPOT happened to fire the TRACK message.

This is all very uninteresting if the SPOT messenger is mounted say on
your parachute harness and inclined or significantly obscured. Tell me
it is out flat in the open and I'll actually care.

Darryl- Hide quoted text -

- Show quoted text -

I don't think I agree with the notion that mounting a spot on the
parachute harness near the shoulder is bad idea. Mine is on the
parachute harness and I get around 10% drops, as good as anyone else
who mounts their Spot perfectly horizontally. I just checked my spot
messages from today: 5 missing messages in 7.5 hours fligh = 10%
Since installing on the parachute harness is the easiest, and provide
easy access during flight, and will stay with you in case of bailout,
I wouldn't recommend against it.

Ramy

On Jul 17, 11:50*pm, Ramy wrote:
On Jul 17, 10:34*pm, Darryl Ramm wrote:



On Jul 17, 9:08*pm, Hellman wrote:

On Jul 16, 7:48*am, Steve Koerner wrote:

I did a serious investigation on the problem involving some
experiments and analysis and I made a presentation to my local club..
My presentation is available for download from my Wing Rigger website:www.wingrigger.com. *(click Extra Soaring Content in lower right
corner).

Steve,

Thanks for that detailed analysis of SPOT behavior. While it helps in
understanding SPOT generally, my question -- and big concern -- is why
that flight was different from all other flights. I don't believe I've
never had more than a 30 minute gap (2 missed transmissions) before,
yet this time the gap was 90 minutes (8 missed transmissions). I was
asking if anyone else had a track from that specific day and time (JUL
15, 1900-2020 Z) and general location (roughly from Oakland, CA to
Lake Tahoe). If so, I wanted to know if they had coverage or also had
around a 90 minute hole in their data.

Martin

Martin

You want to end the guessing game and tell us where your SPOT
messenger is mounted? *On your harness? On your shoulder? Obstructed
by your head? What is the effective field of view of the antenna?

You were tracking roughly the same heading for all that time. *And
that heading (very) roughly lines up with one of the inclined planes
of the GlobalStar constellation.

The GlobalStar satelites orbit in a interweaved pattern with two
inclined planes at +/- 80 degrees or so (you can see a simulation herehttp://www.youtube.com/watch?v=G8VPEueequMoryou can actually play
with the SaVi software shown in the video, seehttp://savi.sourceforge.net).
It is quite possible that things happen like the satelites flying from
the south west to north east are obscured over your left shoudler if
say your SPOT messenger was to the right side of your head and all
those passes could be obscured and maye the next parallel path to the
east is too far away. That leaves the satellites tracking north-west
to south-east and just maybe again if your head partially obscured
those then the satellite does not see the spot until it is further
overhead and out of the optimal bent-pipe geometry to reach the
Alberta, Canada ground station. So maybe in the whole time you just
get maybe one shot when the SPOT fires off its track message where it
manages to see a satellite to get it a bent path to the Texas ground
station. Maybe you just managed to get things timed so bad that you
never happened to have a satellite with bent-pipe view to any ground
station when your SPOT happened to fire the TRACK message.

This is all very uninteresting if the SPOT messenger is mounted say on
your parachute harness and inclined or significantly obscured. Tell me
it is out flat in the open and I'll actually care.

Darryl- Hide quoted text -

- Show quoted text -

I don't think I agree with the notion that mounting a spot on the
parachute harness near the shoulder is bad idea. Mine is on the
parachute harness and I get around 10% drops, as good as anyone else
who mounts their Spot perfectly horizontally. I just checked my spot
messages from today: 5 missing messages in 7.5 hours fligh = 10%
Since installing on the parachute harness is the easiest, and provide
easy access during flight, and will stay with you in case of bailout,
I wouldn't recommend against it.

Ramy

But just don't do that and complain about gaps in your SPOT data. So
folks complaining about SPOT problems lets start with where is the
SPOT unit mounted and how much sky can it see? And Ramy you have been
on here complaining about gaps in your SPOT track in the past. I get
less than 10% drops. The next person with slightly more obscuration
who's flight happens to track the satellites in just the wrong way may
get a lot more. If you don't give them a really good sky view you are
going to see gaps in the data. That is your trade-off, just don't be
surprised when it happens.

Maybe Martin's is mounted with a clear sky view.. who knows.

Darryl

Some comments on the performance of my SPOT during flights this year,
2009, before and after I relocated it from my parachute harness to a
flat position on the forward instrument panel cover. BOTTOM LINE...
place you SPOT in the glider in a horizontal position with an
unobstructed view from horizon to horizon.

I fly "WX" a Discus 2A. Last year and for the first six flights this
year my SPOT was located on my parachute shoulder harness and is
aligned about 45deg to horizontal. Starting with my 06/28/09 flight at
Parowan it was re-located to a horizontal position on the forward
instrument cover.

Here are some statistics on the number of drop-outs during tracking
mode (updates every 10minutes). The percent number is the number of
dropout per flight. The number of track is the total (i.e. includes
the tracks that were lost). Results showed a dramatic improvement:

Date No Tracks No Drop Outs Per Cent Drops

03/15/09 12 2 17%
05/05/09 36 16 44%
06/19/09 22 8 36%
06/22/09 15 3 20%
06/23/09 28 5 18%
06/24/09 19 7 36%

Total dropouts cumulative: 31%

After re-locating to flat orientation forward instrument panel cover

06/28/09 29 0 0%
06/30/09 30 0 0%
07/01/09 25 1 4%
07/03/09 31 1 4%
07/04/09 23 0 0%
07/14/09 37 3 8%

Total dropouts cumulative: 4%

Walt Rogers, WX