GPS interference and contests

[Bill Daniels]

It seems as if GPS interference testing is becoming more widespread.
See: http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf

I wonder if anyone has thought of what might happen if one of these 'tests'
happened near the time an place of a sechduled contest. Basically, you
would lose all GPS systems including loggers. Back to photos? Anyone
thinking about contingencies?

Bill Daniels

[Marc Ramsey[_2_]]

Bill Daniels wrote:
> It seems as if GPS interference testing is becoming more widespread.
> See: http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf
>
> I wonder if anyone has thought of what might happen if one of these 'tests'
> happened near the time an place of a sechduled contest. Basically, you
> would lose all GPS systems including loggers. Back to photos? Anyone
> thinking about contingencies?

This schedule covers days when someone thinks they might want to run a
test, in practice, there are somewhat fewer live tests. The contest
staffs here check NOTAMs daily, if there is notice of a test, they'd
task away from the affected area, or cancel the day if not possible.

I have an IGC file (which I'd be hard pressed to find) from a day when
there was a NOTAMed test at China Lake (roughly 200 miles to the south
of my location), not much to see, except for a few gaps of a couple of
minutes each...

Marc

[JS]

On Jan 17, 9:28 am, Marc Ramsey > wrote:
> Bill Daniels wrote:
> > It seems as if GPS interference testing is becoming more widespread.

As Marc noted, China Lake have been conducting these tests for a
while. It started out mostly on weekdays, bur Saturdays are possible
too.
Several of us have logged flights with holes in them, some quite
large. It does not put a hole in the pressure altitude trace, but may
eliminate your turnpoint. That's the only concern.
One flight last year I was able to campare notes with pilots flying
out of Minden, while I was just North of China Lake. The Minden pilots
had no interference, but my signal was really broken up. The Cambridge
gear seemed to come online rapidly afterwards, but WinPilot had to be
restarted to give me any useful information (I knew the winds were not
at 80 or 90 knots for example)
Watching these logs on SeeYou is interesting. The glider stops,
hovers up and down for a while, then shoots forward 5 miles or so.
Jim

[CindyB]

On Jan 17, 2:25*pm, JS > wrote:
> On Jan 17, 9:28 am, Marc Ramsey > wrote:
>
> > Bill Daniels wrote:
> > > It seems as if GPS interference testing is becoming more widespread.
>
> * As Marc noted, China Lake have been conducting these tests for a
> while. It started out mostly on weekdays,

Bill and all,

Yes, this has been reality in the US for several years.
I managed to warn the 1-26 Nationals about 3 seasons ago, when they
faced blanking/testing for their national contest from Moriarty, NM.
I offered guidance for conversations, and they worked wtih the staff
at
White Sands to adjust the local tests to be prior to launch/flight/
task times.
Otherwise, you are right. Achieving turns could only have been
verified by cameras, again.

I raised the discussion to IGC level, about the possibility of world
record attempts
(which are possible from my site) having pre-launch authorization
possible for
antiquated validation/recording devices ( analog equipment!), but was
pooh-poohed as not having an authentic concern. At that point in
time,
we were hosting the Perlan glider with Fossett/Enevoldsen and it
was a VERY real concern for us. And it still is.

We are fortunate to have a close working relationship, and know on
any given week if jamming will occur for the following calendar week,
locally. It adds to the flight planning considerations.
I can have world class weather, military airspace permission and IGC
approved recording devices, and have a data file that is worthless
for
record documentation.

So, yes, we have tried for contingency planning. They work, within
the US.
And yes, your SSA airspace and technical folks ARE trying to serve
glider pilot interests in the larger sense.

Cindy Brickner
Region 12 Director
SSA Airspace Committee

[309]

On Jan 17, 7:53 pm, CindyB > wrote:
> I raised the discussion to IGC level,
<snip>
> I can have world class weather, military airspace permission and IGC
> approved recording devices, and have a data file that is worthless
> for
> record documentation.
>
> So, yes, we have tried for contingency planning. They work, within
> the US.
> And yes, your SSA airspace and technical folks ARE trying to serve
> glider pilot interests in the larger sense.
>
> Cindy Brickner

Is it worthwhile for us to keep carrying cameras and barographs to
have ammunition that might convince IGC that this IS an authentic
concern? Or maybe ask the Navy to jam GPS near a European contest? :-
P

I agree, the baro part of the logger SHOULD be uninterrupted, making
the more painful camera operations critical in showing the case to
IGC.

I hope that we're not becoming "Logger Cripples" (unable to function
without GPS, Logger, SeeYou, etc.). I'm planning to keep flying with
my backup Replogle and camera -- but then I'm semi-old-fashioned and a
1-26 driver (some read that "masochist"). Isn't the chief function of
the camera to validate rounding the turnpoint (second being
documenting the declaration)? Several years ago, the 1-26 Association
Sweepstakes did away the requirement that turnpoints be "photo
friendly" (i.e., the turnpoint had to be a feature that could be
recognized by photo, leveling the playing field for those that used
cameras instead of GPS's). Similarly, it was just recently that the
1-26 Championships REQUIRED GPS for the contest, mainly in a bid to
reduce the costs (both time and money) generated by film development.
Years ago, my camera & barograph saved my Diamond Goal flight when I
fat-fingered an error in the lat-lon of the first turnpoint for the
logger declaration (though I'd still whine about the Volkslogger's
"comfortable DOS interface").

Many contest and world class pilots have recommended carrying TWO
loggers, for the eventual day when one of them fails. Unfortunately,
in the Jammed GPS environment, one "failure" would render both loggers
unusable (especially at the turnpoint). We as pilots should be able
to see this -- matching the out the window expectation with the GPS
indicated arrival of the turnpoint.

Even though I'm a 1-26'er, I enjoy the training and entertainment
value of loggers and software...and the compelling and "crippling"
moving map display on the PDA. As the seminar title suggests, "help,
my GPS sucked my brains out!"

Thanks for carrying the torch to IGC, even if they're pooh-poohing the
issue.

-Pete
#309

[Marc Ramsey[_2_]]

309 wrote:
> Is it worthwhile for us to keep carrying cameras and barographs to
> have ammunition that might convince IGC that this IS an authentic
> concern? Or maybe ask the Navy to jam GPS near a European contest? :-
> P

I'm curious, what exactly are you expecting the IGC or anyone else to
do? Are you really carrying a camera just in case someone randomly
decides to run a jamming test while you're in the midst of a world
record attempt?

Marc

[309]

On Jan 20, 2:31 pm, Marc Ramsey > wrote:
> I'm curious, what exactly are you expecting the IGC or anyone else to
> do? Are you really carrying a camera just in case someone randomly
> decides to run a jamming test while you're in the midst of a world
> record attempt?
>
> Marc

I am trying to complete my third diamond, for distance, in my 1-26.

Last I heard, the SSA still (for another year?) will award badges/
diamonds with camera and photo documentation.

I mainly fly in the Owens' Valley, which has been subject to at least
a NOTAM indicating that the Navy might jam GPS for each and every day
I've been able to soar there in the last 3 years. They're not random
about it at all. No, I'm not convinced that the Navy is angry with me
over something I did to them -- but that doesn't mean they aren't
angry with me...

FWIW, each of my previous diamond flights set Regional 1-26 Class
records (absolute altitude & gain of altitude in one, and speed over a
300 km closed course for the other). I did not have an IGC logger
aboard for the altitude flight. For the speed record (since shattered
by 1-26 Legend Doug Levy) probably would not have been possible
without GPS.

That third diamond is my secondary focus in any and all of my soaring
activities. Having fun (safely) is my primary objective.

I find it odd that IGC (and soon SSA) have chosen to recognize only
the latest technology for documentation, especially considering that
very few submissions go in "the old fashioned way." Is it laziness?
Both IGC and SSA push the lions' share of responsibility onto the
Official Observer for validating claims and achievements. How
difficult is it to look at the picture, ESPECIALLY given the
popularity of tools that help OO's and IGC do this easily (e.g.,
Google Earth)???

Slightly off topic, all the politics notwithstanding, I really admire
Dennis Wright for getting his silver distance the REALLY HARD way,
flying a 1-26, off of an auto-tow launch, with a honkin' headwind on
the return leg of a declared out and return. Double
Tough...especially considering he could have put on a glass slipper
and damn near coasted.

There have been other threads suggesting that IGC revise the diamond
criteria to take account of glider performance. It would seem to me
that this would be a much higher priority for IGC if you consider the
fact that when the original diamond criteria were conceived, a 30:1
ship wasn't even in anybody's DREAMS. Though I sound bitter, I'm glad
they've left those traditions alone.

If a simple disposable camera can be used with a declaration form to
save a diamond (or in somebody else's case, a world record) from the
Navy's penchant for jamming GPS, then I'm all for it (using cameras
that is, not jamming).

Thanks for starting the topic (again?), Bill.

-Pete
#309

[Brian[_1_]]

<snip>
> I have an IGC file (which I'd be hard pressed to find) from a day when
> there was a NOTAMed test at China Lake (roughly 200 miles to the south
> of my location), not much to see, except for a few gaps of a couple of
> minutes each...
>
> Marc

One of my former students was flying to an airport in the China Lake
area and navigating primarily by GPS during one of the Notamed times.
He had noted the Notam but didn't think much of it until the GPS
showed him as arrived and there was no airport. After fumbling with
the map for a few minutes he figured out the airport was about 5 miles
away from where the GPS said it was.

Brian
CFIIG/ASEL

[7C]

Big problem is proving that you didn't break airspace...

Very hard to do with a camera & barometer!

[ZZ]

Even though this thread is related to GPS jamming affecting contest
flight documentation, please allow me this little rant.

GPS navigation is now fully accepted in the US and there are even some
instrument approaches based upon GPS.

Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
system which is used in air navigation? Pilots who are fortunate not to
live/fly near a military installation who jam these signals can enjoy
the system. The rest of us have to put up with unreliable/intermittent use.


Is this an issue that the AOPA and the SSA should try to address?


Paul




Bill Daniels wrote:
> It seems as if GPS interference testing is becoming more widespread.
> See: http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf
>
> I wonder if anyone has thought of what might happen if one of these 'tests'
> happened near the time an place of a sechduled contest. Basically, you
> would lose all GPS systems including loggers. Back to photos? Anyone
> thinking about contingencies?
>
> Bill Daniels
>
>

[Mike the Strike]

> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
> system which is used in air navigation?

The US military own it, they can jam it or turn it off just as they
please. No law to prevent them.

Mike

[Marc Ramsey[_2_]]

Mike the Strike wrote:
>> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
>> system which is used in air navigation?
>
> The US military own it, they can jam it or turn it off just as they
> please. No law to prevent them.

I don't remember all of the details, but the Department of
Transportation has specific agreements with the DOD dating back to the
early 90s that were put in place to allow GPS to be used to in safety
critical applications (not just aviation, also railroads, timing systems
for the power grid, etc.). Much of the subsequent funding for GPS
satellite upgrades has been explicitly allocated for this purpose. The
DOD can't "jam it or turn it off just as they please", at least within
US territory...

Marc

[Bruce]

That's why the Europeans are building Galileo - or did I miss something...

Only the military mind will conceive something of enormous benefit, develop it
with no concern for economics, then intentionally break it because they can.

So the question, in the litigious part of the world must be - is it legally
defensible, to interrupt a service that does not belong exclusively to you, and
which is used by commercial and private civilian users? Let's hope it does not
take a fatal incident to find out.

ESA has not started "commercial" use of its satellites yet - most of it's
stations are terrestrial at present - so I suppose for the very short term the
view that "we own it we can do what we like with it is valid". By 2010 there
will be two satellite systems. Then what?

Mike the Strike wrote:
>> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
>> system which is used in air navigation?
>
> The US military own it, they can jam it or turn it off just as they
> please. No law to prevent them.
>
> Mike

[mike]

I agree, but it is a National Security issue-Good luck on changing
that.


On Jan 21, 10:22 am, ZZ > wrote:
> Even though this thread is related to GPS jamming affecting contest
> flight documentation, please allow me this little rant.
>
> GPS navigation is now fully accepted in the US and there are even some
> instrument approaches based upon GPS.
>
> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
> system which is used in air navigation? Pilots who are fortunate not to
> live/fly near a military installation who jam these signals can enjoy
> the system. The rest of us have to put up with unreliable/intermittent use.
>
> Is this an issue that the AOPA and the SSA should try to address?
>
> Paul
>
> Bill Daniels wrote:
> > It seems as if GPS interference testing is becoming more widespread.
> > See:http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf
>
> > I wonder if anyone has thought of what might happen if one of these 'tests'
> > happened near the time an place of a sechduled contest. Basically, you
> > would lose all GPS systems including loggers. Back to photos? Anyone
> > thinking about contingencies?
>
> > Bill Daniels

[Bill Daniels]

The military has vast testing ranges in places like Johnson Island in the
Pacific Ocean. They can test jamming there although it's probably more
expensive than China Lake or White Sands.

The reasons for testing jamming of GPS devices is due to well grounded
concerns about post 9/11 civil defense. You can probably imagine scenarios
so there no need to spell it out in a public forum. The latest block of GPS
satellites will have the capability to deny enemy access in a restricted
geographic area eliminating the need for jamming.

Bill Daniels

"mike" > wrote in message
...
>I agree, but it is a National Security issue-Good luck on changing
> that.
>
>
> On Jan 21, 10:22 am, ZZ > wrote:
>> Even though this thread is related to GPS jamming affecting contest
>> flight documentation, please allow me this little rant.
>>
>> GPS navigation is now fully accepted in the US and there are even some
>> instrument approaches based upon GPS.
>>
>> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
>> system which is used in air navigation? Pilots who are fortunate not to
>> live/fly near a military installation who jam these signals can enjoy
>> the system. The rest of us have to put up with unreliable/intermittent
>> use.
>>
>> Is this an issue that the AOPA and the SSA should try to address?
>>
>> Paul
>>
>> Bill Daniels wrote:
>> > It seems as if GPS interference testing is becoming more widespread.
>> > See:http://www.navcen.uscg.gov/gps/gpsnotices/GPS_Interference.pdf
>>
>> > I wonder if anyone has thought of what might happen if one of these
>> > 'tests'
>> > happened near the time an place of a sechduled contest. Basically, you
>> > would lose all GPS systems including loggers. Back to photos? Anyone
>> > thinking about contingencies?
>>
>> > Bill Daniels
>

[309]

On Jan 21, 9:22 am, ZZ > wrote:
> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
> system which is used in air navigation? Pilots who are fortunate not to
> live/fly near a military installation who jam these signals can enjoy
> the system. The rest of us have to put up with unreliable/intermittent use.
>
> Is this an issue that the AOPA and the SSA should try to address?
>
> Paul
>

Because you're a pilot, YOU are LEGALLY required to avail yourself of
all NOTAMS and such in order to legally fly. Yeah, it sucks --
especially when there is conflicting info, hidden info, Major League
Baseball Games and such.

Jamming GPS is just like a NOTAM that a VOR or ILS or Loran navigation
aid is "out of service," whether for maintenance or due to disaster
(e.g., when Filmore VOR "FIM" was burned in 2006 wildfires). The
NOTAM is to warn you that it's up to you to figure out a different way
to navigate (or document your badge/record flight)...sorta' like
warning you that your battery will fail this week...

Yes, inconvenient. Be glad they NOTAM it, rather than jamming without
telling us.

FWIW, I'm a flight test engineer, working on "something" at NASA-
Dryden, and China Lake GPS jamming _this week_ may interfere with my
livelihood.

Fortunately, they can't move the mountains more quickly than NOAA can
publish paper charts...yet.

-Pete

[Greg Arnold]

Does the military ever tell anyone what area is affected by the jamming?
I don't see that in the NOTAM. It seems that would be useful
information.



309 wrote:
> On Jan 21, 9:22 am, ZZ > wrote:
>> Now I ask, NOTAMS or not, why should it be legal for ANYONE to jam a
>> system which is used in air navigation? Pilots who are fortunate not to
>> live/fly near a military installation who jam these signals can enjoy
>> the system. The rest of us have to put up with unreliable/intermittent use.
>>
>> Is this an issue that the AOPA and the SSA should try to address?
>>
>> Paul
>>
>
> Because you're a pilot, YOU are LEGALLY required to avail yourself of
> all NOTAMS and such in order to legally fly. Yeah, it sucks --
> especially when there is conflicting info, hidden info, Major League
> Baseball Games and such.
>
> Jamming GPS is just like a NOTAM that a VOR or ILS or Loran navigation
> aid is "out of service," whether for maintenance or due to disaster
> (e.g., when Filmore VOR "FIM" was burned in 2006 wildfires). The
> NOTAM is to warn you that it's up to you to figure out a different way
> to navigate (or document your badge/record flight)...sorta' like
> warning you that your battery will fail this week...
>
> Yes, inconvenient. Be glad they NOTAM it, rather than jamming without
> telling us.
>
> FWIW, I'm a flight test engineer, working on "something" at NASA-
> Dryden, and China Lake GPS jamming _this week_ may interfere with my
> livelihood.
>
> Fortunately, they can't move the mountains more quickly than NOAA can
> publish paper charts...yet.
>
> -Pete

[309]

On Jan 21, 9:16 pm, Greg Arnold > wrote:
> Does the military ever tell anyone what area is affected by the jamming?
> I don't see that in the NOTAM. It seems that would be useful
> information.
>
See https://pilotweb.nas.faa.gov/distribution/centerQuery.html

or:

!GPS 01/021 ZLA GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A 324
NM RADIUS OF 372023.4N/1160158.4W (LOCATED WITHIN THE TONOPAH TEST
RANGE) AT FL400, DECREASING IN AREA WITH DECREASE IN ALTITUDE TO 277
NM RADIUS AT FL250, 198 NM RADIUS AT 10,000 FT MSL AND 197 NM RADIUS
AT 4,000 FT AGL. THE IMPACT AREA ALSO EXTENDS INTO THE MEXICAN FIR.
1900Z-0845Z DLY WEF 0801211900-0801260845

They're describing a VOLUME about the jamming point: the higher you
are (diamond altitude, a little under FL400), the farther you need to
get away to be "unimpacted." Notice they admit the jamming area
includes Mexican airspace. Do you think Europe might be next? Plot
the lat-lon given in SeeYou, draw your circle at FL250 (yeah, it would
be nice if they gave you 17,999) and if your path flies through that
line, your record might be toast.

They've got reasons for doing this, and in the really long view, I
believe that at least SOME of what they do actually protects my
ability (privilege) to fly and soar.

Is it that difficult for IGC to allow camera backup to Logger GPS
traces? For those that think there's an ulterior motive, I sold my
Kodak stock years ago.

Or should I take up bowling, instead?

-Pete

[Martin Gregorie[_1_]]

Bruce wrote:
>
> ESA has not started "commercial" use of its satellites yet - most of
> it's stations are terrestrial at present - so I suppose for the very
> short term the view that "we own it we can do what we like with it is
> valid". By 2010 there will be two satellite systems. Then what?
>
Technically, there are already two: GLONASS is the other, though I'll
admit I've never seen a receiver for it. I read the other day that it
had rather fallen on hard times, but that the Russians are about to
bring the constellation back to full strength and possibly to open it up.

I wonder if either Galileo or GLONASS will provide better polar coverage
than GPS?

There seems to be some confusion as whether current GPS receivers will
work with Galileo. I understand that the frequencies are similar and the
satellite IDs have been arranged to avoid clashes. I asked this question
after an article on Galileo appeared in New Scientist: apparently the
correct answer is "suck it and see" because nobody knows for sure.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Greg Arnold]

309 wrote:
> On Jan 21, 9:16 pm, Greg Arnold > wrote:
>> Does the military ever tell anyone what area is affected by the jamming?
>> I don't see that in the NOTAM. It seems that would be useful
>> information.
>>
> See https://pilotweb.nas.faa.gov/distribution/centerQuery.html
>
> or:
>
> !GPS 01/021 ZLA GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A 324
> NM RADIUS OF 372023.4N/1160158.4W (LOCATED WITHIN THE TONOPAH TEST
> RANGE) AT FL400, DECREASING IN AREA WITH DECREASE IN ALTITUDE TO 277
> NM RADIUS AT FL250, 198 NM RADIUS AT 10,000 FT MSL AND 197 NM RADIUS
> AT 4,000 FT AGL. THE IMPACT AREA ALSO EXTENDS INTO THE MEXICAN FIR.
> 1900Z-0845Z DLY WEF 0801211900-0801260845
>
> They're describing a VOLUME about the jamming point: the higher you
> are (diamond altitude, a little under FL400), the farther you need to
> get away to be "unimpacted." Notice they admit the jamming area
> includes Mexican airspace. Do you think Europe might be next? Plot
> the lat-lon given in SeeYou, draw your circle at FL250 (yeah, it would
> be nice if they gave you 17,999) and if your path flies through that
> line, your record might be toast.

The 277 nm radius at FL250 roughly covers San Francisco to the west, San
Diego to the south, and Salt Lake City to the east. I am not sure that
this information is terribly helpful for pilots (power as well as
soaring) who would like to know if they can believe what their GPS is
telling them.

>
> They've got reasons for doing this, and in the really long view, I
> believe that at least SOME of what they do actually protects my
> ability (privilege) to fly and soar.

I am skeptical.


>
> -Pete

[hans]

Hi Martin!

Why do you think that GPS has a bad coverage at the poles? The
inclination and orbital altitude of Galileo is a little bit higher than
for GPS, so there is potential for a small performance increases.

Reading the public ICD of Galileo available from
http://www.galileoju.com/page2.cfm and comparing it with the public ICD
of GPS available from
http://www.navcen.uscg.gov/gps/modernization/default.htm you may draw
your own conclusion.

I would expect that current GPS receivers have not implemented the
Galileo ICD. But I seem to remember that some manufacturers claim to be
Galileo ready, but I wounder how they are able to do this from a legal
point of view.

Best Regards

Hans




Martin Gregorie schrieb:
> Bruce wrote:
>>
>> ESA has not started "commercial" use of its satellites yet - most of
>> it's stations are terrestrial at present - so I suppose for the very
>> short term the view that "we own it we can do what we like with it is
>> valid". By 2010 there will be two satellite systems. Then what?
>>
> Technically, there are already two: GLONASS is the other, though I'll
> admit I've never seen a receiver for it. I read the other day that it
> had rather fallen on hard times, but that the Russians are about to
> bring the constellation back to full strength and possibly to open it up.
>
> I wonder if either Galileo or GLONASS will provide better polar coverage
> than GPS?
>
> There seems to be some confusion as whether current GPS receivers will
> work with Galileo. I understand that the frequencies are similar and the
> satellite IDs have been arranged to avoid clashes. I asked this question
> after an article on Galileo appeared in New Scientist: apparently the
> correct answer is "suck it and see" because nobody knows for sure.
>
>

[hans]

From the way they are describing it, it looks like they are sending a
signal from the ground. So there is an easy countermeasure, install a
nullifying GPS-antenna and have the null pointing to the location of the
signal source.

In the beginning of GPS flight recording there where many interfering
signal sources in Italy. The way to overcome the problem was to install
the GPS antenna on a large grounding plane, which made the GPS antenna
to ignore the interfering signal sources.




Greg Arnold schrieb:
> 309 wrote:
>> On Jan 21, 9:16 pm, Greg Arnold > wrote:
>>> Does the military ever tell anyone what area is affected by the jamming?
>>> I don't see that in the NOTAM. It seems that would be useful
>>> information.
>>>
>> See https://pilotweb.nas.faa.gov/distribution/centerQuery.html
>>
>> or:
>>
>> !GPS 01/021 ZLA GPS IS UNRELIABLE AND MAY BE UNAVAILABLE WITHIN A 324
>> NM RADIUS OF 372023.4N/1160158.4W (LOCATED WITHIN THE TONOPAH TEST
>> RANGE) AT FL400, DECREASING IN AREA WITH DECREASE IN ALTITUDE TO 277
>> NM RADIUS AT FL250, 198 NM RADIUS AT 10,000 FT MSL AND 197 NM RADIUS
>> AT 4,000 FT AGL. THE IMPACT AREA ALSO EXTENDS INTO THE MEXICAN FIR.
>> 1900Z-0845Z DLY WEF 0801211900-0801260845
>>
>> They're describing a VOLUME about the jamming point: the higher you
>> are (diamond altitude, a little under FL400), the farther you need to
>> get away to be "unimpacted." Notice they admit the jamming area
>> includes Mexican airspace. Do you think Europe might be next? Plot
>> the lat-lon given in SeeYou, draw your circle at FL250 (yeah, it would
>> be nice if they gave you 17,999) and if your path flies through that
>> line, your record might be toast.
>
> The 277 nm radius at FL250 roughly covers San Francisco to the west, San
> Diego to the south, and Salt Lake City to the east. I am not sure that
> this information is terribly helpful for pilots (power as well as
> soaring) who would like to know if they can believe what their GPS is
> telling them.
>
>>
>> They've got reasons for doing this, and in the really long view, I
>> believe that at least SOME of what they do actually protects my
>> ability (privilege) to fly and soar.
>
> I am skeptical.
>
>
>>
>> -Pete

[Martin Gregorie[_1_]]

hans wrote:
>
> Why do you think that GPS has a bad coverage at the poles? The
> inclination and orbital altitude of Galileo is a little bit higher than
> for GPS, so there is potential for a small performance increases.
>
For some reason I thought the constellation was in low orbits and so had
limited polar visibility. I was wrong there.

It turns out GPS uses a 25,000 km orbit, inclined at 55 degrees to the
equator. The orbits reach 55 degrees north and south, which gives plenty
of polar visibility. There will still be at least 4 satellites visible
at any time. The satellites are closer to the horizon in polar regions
so positional accuracy isn't affected, though I suppose shielding by
surface features could be more of a problem than it is at lower latitudes.

However, height accuracy must deteriorate close to the pole because the
satellites are never overhead: you get max vertical accuracy with 3 or
more satellites near the horizon and one overhead.

> I would expect that current GPS receivers have not implemented the
> Galileo ICD.
>
I'm certain you're right, especially about the units with the original
Garmin 12 channel receivers (12XL, II+, III+, GPS35 etc), because apart
from anything else its hard to imagine that these could cope with the
different time codes used by GPS and Galileo. The time conversion
algorithms must have been published long after these receivers were
designed.

Thanks for prodding me into doing a quick search for the stuff I didn't
know.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[[email protected]]

On Jan 22, 3:55 am, 309 > wrote:

> Or should I take up bowling, instead?
> -Pete

Don't do it ! But if you do take up bowling we'll want to see it on
You tube ;-)
See ya, Dave

[309]

On Jan 22, 5:31 pm, wrote:
> On Jan 22, 3:55 am, 309 > wrote:
>
> > Or should I take up bowling, instead?
> > -Pete
>
> Don't do it ! But if you do take up bowling we'll want to see it on
> You tube ;-)
> See ya, Dave

I haven't been bowling lately...have they transitioned to GPS loggers
for scoring? ;-)

-Pete

[[email protected]]

On Jan 22, 10:37*am, Greg Arnold > wrote:
> 309 wrote:
> [...]
>
> The 277 nm radius at FL250 roughly covers San Francisco to the west, San
> Diego to the south, and Salt Lake City to the east. *I am not sure that
> this information is terribly helpful for pilots (power as well as
> soaring) who would like to know if they can believe what their GPS is
> telling them.
>
>
> I am skeptical.
>

But pilots should always be skeptical about black box navigation.

The GNSS (Global Navigation Satellite System, a name that encompasses
all satellite navigation systems) community is well aware that jamming
has an effect on civil air traffic, powered and glider. That's why
the AIM outlines a procedure for medical flights to request that the
tests
be stopped. I have done a lot of medical flying, and a lot of those
small mountain airports have GPS approaches. If I had needed
the approach I could have asked ATC to ask the controlling agency to
stop the test. I'm sure this would have been an expensive proposition
for them, but there is also a strong life preservation ethic among
GNSS
engineers and operators. They go to work with the motto that
"Someone,
somewhere is depending on my work to save his life."

The latest word is that enhanced LORAN will be preserved as a
backup to GPS. I have never heard of a glider with a LORAN
receiver, nor have I heard of a handheld LORAN receiver, but
it might be something to consider. Many aircraft have inertial
reference units to supplement GPS; these are light but drift, so
usually there is some kind of Kalman filter blending the
solutions. One can also use DME/DME updating if there
are enough DME stations in sight, but DME uses a ton of
power and is unsuitable for gliders.