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Comment by wil421 | Hacker News Reader

I have been doing this for years on my gameboy/sega/iphone/ipad/mac. I even turned my airplane mode off to see how long it would take to loose service last time I flew. (I dont fly very often)

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How long does it take? On my last flight the man sitting next to me started receiving SMS many, many meters before landing

I was a passenger sitting in the co-pilot's seat on a small plane in Africa, the pilot was texting during the flight even at 10,000 feet ^_^.

That happened to me too (except in Venezuela).

I had a similar experience, small plane over a relatively hilly area in Zambia. It took me a bit to get past the assumption that the vibrating around my leg wasn't a structural problem with plane....

It was pretty soon after I don't know the altitude but it was within 5 minutes of leaving the ground.

I saw a passenger next to me texting at 37k feet over Kansas on an JFK-SFO flight once. It was SMS, not iMessage (the message bubbles were green). How did he get signal up there?

Easily, he's in line of sight to tons of radio towers.

yes, GSM limit is about 35km, while 37k feet is about 11km, so looks like it should work. We perceive height differently than length.

He's probably got better signal there than I do down here on the ground. Cell towers have a range of about 5km at the absolute minimum, and a whole lot more than that if there's no hills in the way (e.g., if the phone is directly above them).

Yes but the cell towers also have directional antennas, not wanting to waste any of their total allowed transmission power beaming it into space...

Yes, in densely populated areas with high frequencies (3G/LTE). In more rural areas the antennas cover a bigger area. My experience in light aircraft (operating below 10000 feet) is that 2G GSM connectivity is pretty good, 3G not so much.

Actually directional antennas make no difference in regard to their allowed transmission power. The allowed power is specified as EIRP (Equivalent isotropically radiated power), which specifies the power a perfectly isotropic antenna emits. So if you increase the gain of your antenna, you have to decrease the amount of power you feed into your antenna to stay inside legal bounds (assuming of course you were at the maximum allowed transmission power to begin with).

What you do gain however is gain on the receive path (so you can hear the mobile phones better). Also the possibility to build segments and thus increase the usage of your frequency bands.

In my limited experience (not on an airliner, so actually legalish), signal is usually good below 4,000ft, almost guaranteed to be gone above 6,000ft, and hit or miss in between.

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