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(Sorry, I don't know if this is the right forum for this question, but maybe someone will know the answer. If not, which StackExchange forum could be more suitable?)

Me and a few friends of mine are planning to build a remote controlled balloon probe. As there already were many projects involving stratosphere flights, we are rather trying to go just a few kilometers high, but establish a permanent data connection. The problem is that where I live (Germany), operating quite much any RF module with sufficient range is illegal for people without a radio license, which we happen not to have.

So instead of that we are thinking of connecting a RasPi to a 3G dongle and transmit our data over a TCP connection. But how high does the signal of cell towers usually reach? I have read very contrary opinions about this. And how good is the quality of a connection up there? Is it sufficient to send greater chunks of data like low-res pictures? Maybe it might be important that mobile connections in airplanes have the additional problem of needing to change cell towers very frequently because of the high moving speed, which would not be the case in a slow-moving balloon probe.

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    $\begingroup$ Similar question: electronics.stackexchange.com/questions/94668/… $\endgroup$
    – user4182
    Commented Nov 4, 2015 at 1:54
  • $\begingroup$ Not an answer, since I don't know in practice, but I expect that one of the issues is going to be the fact that quite often, base station antennas are tilted downward (mechanically or electrically), so that the peak of their radiation diagram points towards the ground. This could create big issues with reception. I did manage to receive a message using SMS in an airplane once, despite that though. $\endgroup$
    – AndrejaKo
    Commented Nov 29, 2015 at 21:31

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I am by no means an expert, but here's my point of view on this. Cellphones get their data by a Cell Tower, and if you have ever been on a plane there is little to no reception once you are in the air. The reason this happens is because the cell towers are horizontally directional so that they can get the most range from the smallest amount of power possible. They don't waste RF by sending it up. I know it's not the answer your looking for, but I hope it helps!

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Clearly not possible if you try to reach a certain altitude. Why?

Because antennas of cell phones are made -by design- to "spread" the signal on a horizontal plan.

If you are to high in the sky, you cannot listen, nor speak to cellular antennas.

Turn your chance on VHF spectrum instead.

No chance to make a world-around balloon with no repeater.

Planes are using a local cell repeater itself, then forward traffic through plane-to-land special uplink or plane-to-sat special uplink.

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    $\begingroup$ That aircraft which offer cell phone service to passengers use a downlink separate from the regular cell network base stations has many other reasons as well. For example, the cellular networks simply aren't designed to cope with something that is moving at approximately 250 m/s (which is 800 km/h, which is a common speed for large passenger aircraft). See for example Why aren't cell phones allowed to be used in aircraft? on the Aviation SE. $\endgroup$
    – user
    Commented Dec 11, 2015 at 8:49
  • $\begingroup$ Cell phones are used at all angles. They have to be omnidirectional if they can pick up signal both upright and sideways. This argument doesn't hold much merit. $\endgroup$
    – PearsonArtPhoto
    Commented Dec 14, 2015 at 0:59
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    $\begingroup$ We don't speak about cell phones, but about repeaters on cell masts. $\endgroup$
    – mat.viguier
    Commented Dec 14, 2015 at 2:31
  • $\begingroup$ @mat.viguier: Cell towers transmit using omnidirectional antennas but receive using directional antennas that are pointed slightly downwards. Someone 50+ meters above probably wouldn't be able to connect. $\endgroup$
    – Old_Fossil
    Commented Sep 13, 2017 at 4:54
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UHF/VHF is your bands for this application. You can talk to the International Space Station on VHF. Line of sight is no issue in a flying object. You need to choose a band that is used for digital transmissions and then have a digital receiver. Set up packet radio and then control whatever you want and get your camera image and telemetry streamed down.

I have tested the cell phone reception in airplanes during take-off, and that works fine for drones. But as you want to go into the stratosphere, you lose the cell tower connection.

The key for very high flights is decent antennas of course.

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