China no GPS

Hi,
Is there something going on with China?

My friend took his Garmin NUVI GPS loaded with maps of China but the GPS
would not work there.

He could not pick up any position fix at all.

Come back to Australia and all works as normal. Took a trip to New Zealand
and all works as it should.

Does anybody have any idea what is going on there?

I was always under the impression GPS works everywhere.

Early in the days of GPS China would not allow them into the country but
that seems to be no problem now.

Have they found a way to spoof the signal??

Thanks
Oliver Fleming

On Mon, 1 Nov 2010 13:06:45 +1000, "Oliver Fleming"


If you move the gpsr over 300 miles while it is OFF, it will take a
while to download a new Almanac and ephemeris data from the
satellites.

It should be turned on a left a while with a clear view of the sky for
I would say, at least 21 minutes. Was that done? Or did your friend
just turn it on and expect an Instant Fix?

On 10-11-01 1:14 , Nicholas wrote:


Eh? The Almanac does not change according to your position, nor does
satellite ephemeris at a given time. What has changed is ... well, your
position.

Most receivers will lock on reasonably quickly after a moderate offset -
certainly within about 5 minutes after a large offset. I've done this
many times on international trips.



--
gmail originated posts filtered due to spam.

On Wed, 03 Nov 2010 17:29:27 -0400, Alan Browne


Nobody knows with certainty =all= the factors that were at play during
the time the Nuvi couldn't acquire a signal fix. Therefore it is
impossible to say =with=certainty= exactly what "the problem" was.

I haven't traveled internationally since my 2 heart attacks in 1987.
Today, I'm a Cyborg living with a computer in my chest that controls
my heart. I won't be doing any long-range travel in the foreseeable
future.

I have both ancient gpsrs and some of the newest models. I haven't
run the ancient stuff in a long time, so I would wager 1 U.S. penny
that if I put batteries in them and turn them on, it will take about
20 minutes to get a lock. The newest stuff? Since I use these
regularly, they already have up-to-date Almanacs in them.

Lg

ur
g

If the Nuvi has a satellite status screen like my cheap Garmin GPS12,
then you can clearly see what's going on.
Notice if any satellite is reaching a full lock at all (hollow bar
means it has identified the PRN code from the satellite, but doesn't
have signal quality/ephemeris data for pseudo range measurements).
If it's serious ionosferic scintillation, you might see frequent drops
of signal (from full bar back to hollow), which I see often in my home
town as 20 degrees south, specially in the summer. I'm able to obtain
a 3d fix and even have 6+ satellites in view, but I always loose one
or two satellites for a few seconds every minute due to scintillation.
Multipath can agravate this (signal reflection from the ground,
trees, ...).
I'm saying this since you mentioned china-vietnam border, which is
about 22 degrees north, a very much tropical weather area, with a very
active ionosphere, much like my home town.