iPhone in a glider?

Alan wrote:
In article %K%Ak.553$8v5.378@trnddc01 Eric Greenwell
writes:

More phones means the cells have to be smaller. Many/most of towers
around here have a number of what appear to be VERY directional
antennas, and the towers are low ( 100'), and surely very low
power, because the next tower is only a mile or two away. They
aren't going to reach out to 5 miles, even under the best of
conditions.

On the ground, where there are obstacles, that is true. To an
airborne receiver, the range is much farther.

And yet, I can have good service on the ground, but poor or no service
in the air, over the same area. It's not about obstacles, but antenna
patterns, power, and how the system handles a phone that is reaching
multiple towers.


Don't be sure about that low power -- the directional antennas have a
fair amount of gain. The FCC allows 500 watts per channel of
effective radiated power, but 100 watts is a more common figure.
(See: http://www.fcc.gov/cgb/consumerfacts/rfexposure.html ).

From the article:

"the majority of cellular or PCS cell sites in urban and suburban areas
operate at an ERP of 100 watts per channel or less".

The "or less" is important, as a small cell doesn't require much power.
The ERP is obtained with directional antennas, so while it might seem
high, the vertical angle coverage is very shallow. A cell set up for an
Interstate highway will have to use much more power as the cells are
farther apart, and the pattern might be broader, so aircraft near a
highway might experience better reception.


Even a very small amount of power to them will provide far more than
5 miles range.

In fact, one of the noted problems of GSM is that the timing of the
system is the timing induced range limit of about 25 miles, but an
extended variant increases this substantially. Fishermen off the
coast of the U.S. use cell phones out well past 25 miles.

And maybe a cell phone used in the air in those areas would work well.
It's not a place glider pilots have much experience with! THe coast is a
different situation than a inhabited area, and I'm guessing the antenna
power and pattern are likely quite different because of that.

I have used cellphones over 8 miles offshore, and apparently glider
pilots carry them in case of land outs in some pretty remote areas.

And with the full expectation that it will be pure luck if it works; for
example, my phone does not work on sections of major highways in Nevada,
so expecting to work in most areas off the highway is unwise. That is
why the SPOT device is becoming so popular, along with PLBs, in addition
to the usual ELTs and aviation radios. Also, pilots try to radio their
position while in air before landing, because they know using a cell
phone or aircraft radio on the ground is going to be unreliable.

--
Eric Greenwell - Washington State, USA
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