Cheap, long range, wireless data connection?

Soldato
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Here's a question;

Is there anything out there that can provide a relatively cheap data connection (Ideally over about 20KBps) wirelessly, up to about 20kms or more in direct sight? One more rule to the game; It can't rely on networks etc that work on the ground, as I'm wanting it for something 20kms UP (as in towards space). :D

so far I have found radio modems, an am doing a bit of reading, but wondered if there was anything else out there.
 
Man of Honour
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Laser is a good option, but the range is pushing it and they're sensitive environmental conditions (such as: rain, fog, mist, haze or anything which isn't 20:20 visibility).

Microwave is the usual technology for this sort of thing but I think you'll struggle for cheap (and if you're talking 20km upwards, I'm assuming you aren't launching a full blown space mission so you're likely looking for something fairly compact and lightweight too)

Most other technology uses licensed frequency, which obviously means a license, which is probably a killer on cost grounds already.

Only two cheap-ish options I can see are laser (with it's limitations) or something GSM based might be possible (though I can't think of an exact setup right now). Microwave could be worth investigating but I suspect cost and bulk will be an issue...
 
Man of Honour
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Forgive me, but why not directional antennas for a wifi link?

To get that kind of range you'd need to exceed the legally allowed power output I'm fairly sure (or have a very sensitive reciever and very little background noise).

For reference GSM signals basically have a maximum (theoretical range of 22 miles (around 100,000 feet), which makes even that marginal. So you're getting pretty specialised. Good news is you don't want heaps of bandwidth at least - other question is do you need two way comms?
 
Associate
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with a decent pair of attena and a clear line of site 20km should be possible, but your looking at +20db gains here, and thats quite expensive

edit: forgot about power output laws (damn! )
 
Soldato
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Thanks for the suggestions. I think I can rule laser out due to how accurate it would have to be aimed, and problems with clouds etc.

To get that kind of range you'd need to exceed the legally allowed power output I'm fairly sure (or have a very sensitive reciever and very little background noise).

For reference GSM signals basically have a maximum (theoretical range of 22 miles (around 100,000 feet), which makes even that marginal. So you're getting pretty specialised. Good news is you don't want heaps of bandwidth at least - other question is do you need two way comms?

1 way comms would be fine tbh, although 2 way would be a bonus. Basically I'm thinking of launching a high altitude weather balloon, but would like to to transmit image data down as it goes up. A target of 100,000 feet would be great, so as you say GSM is marginal, but still an option.

One option that looks possible is something like;

http://www.digi.com/products/wireless/point-multipoint/xbee-pro-868.jsp
 

J.B

J.B

Soldato
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I've used digi stuff before on a project, its pretty good if your good with the old electronics and code you will get it working no problem.

Personally I think it's probably the best option.

Are there different rules on what can be used (RF wise) at altitude?
 
Man of Honour
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Thanks for the suggestions. I think I can rule laser out due to how accurate it would have to be aimed, and problems with clouds etc.

1 way comms would be fine tbh, although 2 way would be a bonus. Basically I'm thinking of launching a high altitude weather balloon, but would like to to transmit image data down as it goes up. A target of 100,000 feet would be great, so as you say GSM is marginal, but still an option.

One option that looks possible is something like;

http://www.digi.com/products/wireless/point-multipoint/xbee-pro-868.jsp

Looks like a good option if you have the experience to integrate that module into a communications system.

GSM is maybe an option as you say, if you send it straight up above a base station, any lateral movement and it'll drop pretty quickly I'd expect though.

Interesting project anyway!
 
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