GPS anywhere in the world

HI

I am new to this group. I have a couple of questions about use of the
signals from the US GPS satellites.

1. Can anybody use the unclassified signals and build a GPS receiver
anywhere in the world?
2. Is there any US goverment licensing required to use these signals?
3. Are GPS signals equally available all over the world?
4. Is a basic GPS receiver that shows longitude/lattitude/altitude
going to work equally well in an open unobstructed place anywhere in
the world?
5. If US GPS satellite signals can be used by anybody, anywhere in the
world, what is the need for development of Russian, Chinese, European
GPS systems. Is it just to have the higher precision GPS which is
classified in the US systems.

Thanks for your answer. I looked around the web and this group. I
think I know the answers to some of these. But I would like to hear
from people who are more familiar with the details of the GSP systems.

-Dipu

dipumisc@hotmail.com wrote:

Yes.


No.


For the most part yes. There might be some problems in the high
latitudes due to the orbital inclination of the GPS sats.


As long as you can see the satellites you will be able to determine your
location. Some locations are subject to "Selective Availability" which
is controlled deliberate degradation of the GPS signal.


The Russian, Chinese, European do not want to be at the tender mercies
of the United States Air Force. The military GPS signals are classified
and available only to the US Government and select other organizations.
Differential GPS is precision and available to anyone with the receivers .


Dave N

Selective Availability was turned off in 2000. The way it works, it
can't be applied to just SOME areas, at least not relatively small areas.
For a given bird, it's ON, or OFF.


location. Some locations are subject to "Selective

Chuck Tribolet wrote:
location. Some locations are subject to "Selective

Turning SA off was the only good thing that Clinton did as president.
However it may be applied to specific areas by the USAF controllers when
ever they are ordered to.
Specific areas can defined as combat zones and their surrounding areas.
Areas such as Afghanistan and Iraq.

This is why the Europeans want their own GPS systems.

Dave N

wrote:


No it may not!

With twenty-seven(?) active satellites, with each satellite
'illuminating' slightly less than an earth hemisphere (do the math)
please explain how SA can be applied to a 'specific' area.

In your other post you mention 'there might be some problems in the high
latitudes due to the orbital inclination of the GPS sats'. The poorest
coverage is in the mid-40s latitude and there are no problems at high
latitudes.

--
Alan White
Mozilla Firefox and Forte Agent.
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll,
Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather