On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio. If the roof is plastic or cloth you might get
signals, otherwise the glass.

Casady

On Mon, 05 Jan 2009 18:04:26 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio.

As a strict statement, that is true, however radio signals can bend
around objects (demonstrated by radar's ability to see behind
objects). As such a car presents the opportunity to receive signals
inside by virtue of the physics of radio wave propogation and the
ability to move along the surface of metal.

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

--

"Every normal man must be tempted at times
to spit on his hands, hoist the black flag,
and begin to slit throats."

H. L. Mencken

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

Tin-foil hats don't work?
Oh wait, that's "different" waves.
I thought Maxwell Smart had this stuff figured out with the cone of
silence.

--Vic

On Mon, 05 Jan 2009 18:18:34 -0600, Vic Smith
wrote:

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

Tin-foil hats don't work?

http://www.stopabductions.com/

Oh wait, that's "different" waves.

http://www.lessemf.com/personal.html

I thought Maxwell Smart had this stuff figured out with the cone of
silence.

http://www.osha.gov/SLTC/radiofreque...theffects.html

--

"Far better it is to dare mighty things,
to win glorious triumphs even though
checkered by failure, than to rank with
those poor spirits who neither enjoy nor
suffer much because they live in the gray
twilight that knows neither victory nor
defeat."

Theodore Roosevelt

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

On Mon, 05 Jan 2009 18:04:26 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio.

As a strict statement, that is true, however radio signals can bend
around objects (demonstrated by radar's ability to see behind
objects). As such a car presents the opportunity to receive signals
inside by virtue of the physics of radio wave propogation and the
ability to move along the surface of metal.

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

That is true enough, but you generally need to have a view of the sky
unblocked by solid metal. The closer to the glass, the more signal you
get. No problem in an open boat, or inside a fiberglass pilot house.
Now tell how me the cell phone worked inside a steel ship a thousand
miles from land. Magic, obviously. Nothing on the bill from either the
ship or the phoneco, so it must have been magic.

Casady

On Tue, 06 Jan 2009 00:34:07 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 17:01:19 -0500, Tom Francis - SWSports
wrote:

On Mon, 05 Jan 2009 18:04:26 GMT, (Richard
Casady) wrote:

On Mon, 05 Jan 2009 09:40:21 -0500, Dave Brown
wrote:

Does anyone have any experience with working the GPS from the centre of
a moving vehicle? Does it need to be near glass to receive signals?

Metal blocks all radio.

As a strict statement, that is true, however radio signals can bend
around objects (demonstrated by radar's ability to see behind
objects). As such a car presents the opportunity to receive signals
inside by virtue of the physics of radio wave propogation and the
ability to move along the surface of metal.

The only way to completely restrict the reception of radio signals is
to build a grounded solid metal box of some sort or use a grounded
fine wire mesh in which the gaps are less than 1/100th of the base
line wavelength.

That is true enough, but you generally need to have a view of the sky
unblocked by solid metal. The closer to the glass, the more signal you
get. No problem in an open boat, or inside a fiberglass pilot house.
Now tell how me the cell phone worked inside a steel ship a thousand
miles from land. Magic, obviously. Nothing on the bill from either the
ship or the phoneco, so it must have been magic.

Repeaters. Scientific Atlanta builds them into the TV cable systems
onboard cruise ships. Same for two way radio systems in hospitals,
industrial plants and maintenance for large office buildings. Being
digital it's pretty simple to do - spread spectrum receivers and
digital routers out to the transmitter. I would assume that the cost
is built into the price of your cruise ticket.

Or if you prefer, FM.

As in F*ckin' Magic. :)

I saw the coolest thing the other day in the new town ambulance. They
can take a cardiogram and transmit it direct to the ER via secure
encrypted radio link giving real time data for evaluation. The
attending can order drug intervention at that time to the Paramedic.
Everything is recorded on mini-disc - blood O2, saturation, BP -
really neat stuff. My understanding is that even defib can be
controlled from the hospital if there isn't a Paramedic onboard. Kewl.

Bay State's Hospital Pedi unit has a new ambulance that is completely
state of the art for patient transfer - monitors everything enroute in
real time back to the hospital with an attending on immediate call if
something goes south - like a neo-natal transfer. Far cry from the
old days when it was a wing and a prayer and all analog
communications.

Neat stuff.

On Mon, 05 Jan 2009 21:14:15 -0500, wrote:

I was always curious why cell phones etc work so well in airplanes,
even at altitude.
My wife was surfing on her Blackberry all the way to Pennsylvania.

Same deal.

--

"An idealist is one who, on noticing that
a rose smells better than a cabbage, concludes
that it will also make better soup."

H.L. Mencken