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Wireless DATA Link
Gepeto_42 writes "Somebody asked me to help him find a way to get a data link from the coast to a little island where he's gonna have his business (I can't give too much details, it's still secret). The island is at about 10kms from the coast. Is there something else than HAM that could work? Micro-wave? It's in Quebec, Canada, by the way." Probably the best solution would be the 802.11 wireless LAN cards with a souped-up antenna - I'm pretty sure that people have made these work farther than 10km.
the biggest problem with sending anything over long distances is packet latency. you can have unlimited bandwidth, but if you have high latency, your overall service level goes down.
anything that is satellite based will add quite a bit of latency (what i've heard is about 400ms each way).
802.11 is pretty much out of the question. it's slower than microwave, and has the distance problem. large signal amplifiers could probably make it work, but i doubt it would be very robust at that distance. 802.11 also decreases in overall bandwidth the more distance between nodes.
microwave technology can go about 30 miles, and has pretty low latency. you'll need some land on the mainland (rent tower space) to put a microwave dish, and another tower on your island (or whatever it is). i've setup and used one-way microwave connections, and they're suprisingly fast (i was about 15 miles from the tower). microwave is also good for cooking passing birds, but that's a different story.
if you'd like to read a little up on this technology, www.thebeam.com sells commercial and residental microwave packages. most of them include tv also. i don't work for them, i just admire their technology.
Why read the article when I can just make up a snap judgement?
I don't buy this bird-cooking stuff, at least not at the scale this fellow is talking about. Although I grant it might be possible for, say, commercial TV transmitters. Check out this link, for example:
http://www.wirelessmountain.com/superl inkspecs2.html
It's a 10baseT microwave link that will do 15 km with an output power of a whole 50 watts. My 1200 watt microwave might be sufficient to cook a very small bird in a minute, but 4% of that power isn't likely to do much.
A back-of-envelope calculation suggests that even if a small bird like a grashopper sparrow were to absorb 100% of the power of this beam and was perfectly insulated by its feathers, it would heat up by about 0.7 deg C per second. That's slow enough that it certainly won't cook a bird flying through the beam; the bird would somehow have to perch right in the beam and stubbonly stay there despite feeling uncomfortably hot. Oh, and when it passed out it would have to somehow stay in the beam to actually get to cooking temperatures.
And of course in real life, the bird won't absorb anything near 100% of the power, and would lose a lot of the gained heat to the air around it. So if the original querent sets up one of these microwave links, he should plan to keep getting his fried chicken the usual way.
The most important piece of the puzzle was left off of this question. At what speed is the connectivity needed? Another question would be what level of reliablity.
First of all, let me qualify the following information with the fact that water changes things. A lot. Especially at frequencies up in the ghz, where water is essentially a mirror. That said, running a link across this much water isn't impossible, it just takes some engineering work.
The first piece of information I want to provide is that you can do a 2.4ghz 802.11b link at 11mhz over this distance with the right antenna system without even breaking a sweat. There is sufficient link margin for 99.99+% uptime. I have links running over 20 miles without any problems at all. You should also have almost no interference problems in the environment I envision. Again water will be an issue, but you should be able to work around that. This would provide a 11mb/s radio rate (About 5-8mb/s usable) link. This would be cheap. About $2000 an end when you get done putting together all the pieces. Towers not included.
Using different equipment, I can go up to 15 miles (24 km) at 93Mb/s. Assuming this is 10km or less, I can also go up to 7 miles (11km) at 420Mb/s (Full Duplex, 840mb/s aggregate). Of course these are much much much more expensive.
All of the above options are license-exempt, which basically means that at least in the US you don't need a license. I think that Canada is in the same boat, but I would have to do some more research. There are also licensed options.
To hopefully drive home the point above. You need to find someone qualified to do the engineering on this. It is NOT as easy as it looks. I find that most "experts" on this either are in the category of "I've done a couple of these and they work" or "I couldn't make them work". You need to find someone who understands the inner workings of why these work or don't. If they don't know about path loss calculations, freznel zones, etc. etc. etc. then they're probably not going to be any good to you.
I normally don't try to market my services when I post. However, if you can't find someone you feel is qualified or if you'd like me to look over someone elses design, drop me an email.