GPS interference and contests

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/moder...on/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.

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/distrib...nterQuery.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 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 |

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

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

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.