General Question

john65pennington's avatar

At what altitude does cellphone service cease to operate?

Asked by john65pennington (29080 points ) June 16th, 2011

We’ve all been in an airplane that is about to take off. On the ground, cellphone service operates normally. Question: at what altitude does regular cellphone service cease to function? 5,000 feet? 10,000 feet???

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6 Answers

wundayatta's avatar

There are a number of forums out there where people try to answer this question. This one says that the answer is that it varies. It depends on how many people are using the cell phone tower. More people, and they install a tower with lower wattage so it doesn’t go as far.

Also, the more people who use a cell phone tower, the lower its range. I imagine that airports are probably particularly filled with cell phone traffic.

The maximum range in the US for a CDMA tower is 38 miles. It’s 15 miles for GSM. That requires a tall tower in the mountains and more powerful equipment (in terms of wattage).

Anyway, the answer to you question depends on your carrier and the strength of the towers and how many people are using the towers, and probably more. I can’t tell you a specific altitude.

Lightlyseared's avatar

The maximum design range of a GSM signal is 35km. Other techs like CDMA have no max range and could transmit upto 70km (depending on conditions and cell phone). A 747 cruises at 11,000m (or 11km) so you should be able to pick up a signal in flight. As a sidenote I’ve found you get excellent cell coverage at the top of many high mountains.

robmandu's avatar

Has never been able to pick up any kind of cell signal on various handsets over the years whenever the plane is in the air.

Note: this is usually noted after discovery that the device was inadvertently powered on.

gasman's avatar

There’s another factor take into account with “range” from a transmitter. Most cell transmitters (image) seem to be composed of vertical elements arrayed horizontally, suggesting that the microwaves are beamed toward the horizon. Microwaves aren’t necessarily line-of-sight, but they’re more directional than ordinary radio. Radiation upward into the sky would be a huge waste of power and is no doubt minimized in the design of transmitters. Ordinary radio radiates little power upward (picture power as a bagel surrounding the mast). So my educated guess is that you’ll lose cellular service at an altitude much lower than the same distance on the ground that we normally consider the transmitter’s range.

Also: On the ground you’re normally close to just one or two transmitters at a time, with one cell in the network imperceptibly handing off your call at a different frequency to the next cell you move to. From the air, however, multiple cells would be visible at once at nearly the same range —I’m not sure how the network would handle that?

Lightlyseared's avatar

So I found some research on the subject from 2003. A successful call was made at 8000 feet above London Ontario. However it took several attempts to connect and signal quality was poor. At 6000 feet signal quality was better bit it still took several attempts to connect.

meiosis's avatar

You can definitely get a signal at 29,029 ft (8,848m)

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