Cheap, long range, wireless data connection?

Messiah Khan · 16 Sep 2009 at 10:34

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).

so far I have found radio modems, an am doing a bit of reading, but wondered if there was anything else out there.

howler · 16 Sep 2009 at 11:01

Cheap is going to be the killer for you there, you could look at laser

bigredshark · 16 Sep 2009 at 13:02

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...

Azuse05 · 16 Sep 2009 at 13:13

Forgive me, but why not directional antennas for a wifi link?

bigredshark · 16 Sep 2009 at 13:19

Azuse05 said:
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?

quickshot89 · 16 Sep 2009 at 13:19

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! )

Messiah Khan · 17 Sep 2009 at 13:32

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.

bigredshark said:
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 · 17 Sep 2009 at 14:14

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?

bigredshark · 17 Sep 2009 at 14:24

Messiah Khan said:
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!