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I am looking for a way to construct a two-way communication channel between remote hosts (far away), in big electric smog (large city), but where the weather is mostly clean (some rainy day is not a problem).

I think it could be relatively easily solved by tunneling rs232 through a modulated laser, and tunneling ppp into that rs232.

Unfortunately, googling for different laser solutions, I've found only industrial solutions and nothing in the home budget size.

Do they exist? Its technology probably isn't much more complex, as an infrared tv controller.

  • What range and bandwidth are you aiming for? – Cees Timmerman Oct 7 '15 at 19:55
  • @CeesTimmerman Some km. Fewer than 5. – peterh Oct 8 '15 at 16:08
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A Nikon Coolshot 20 6x20 Laser Rangefinder is weatherproof, easily to aim, and works up to 500 meter, for 166.95 USD. Using one of those at each end should allow for communication up to 1 km, provided you can modify them: electronics.stackexchange.com should be able to help.

Cheaper still is Ronja (Reasonable Optical Near Joint Access), at 60 USD + 70 man hours for a 10Mbps optical communication link at distances of up to 1.4km. Lasers instead of LEDs might double that range to 3.0 km, or more if licensed or reckless.

The best and cheapest option would be WokFi:

WokFi antennas are fabricated out of commonly available concave metal kitchen dishes or dish covers (which need not be perfectly parabolic); Asian woks are favored because they have shapes closest to parabolic. A commercial Wi-Fi antenna, usually a USB Wi-Fi dongle, is suspended in front of the dish, attached by cable to the computer.

Medium WokFi setup

WokFi gains are typically 10+ dB, with range boosts, thus can be 16-32 times over a bare USB adapter. Ranges (LoS) are typically 3–5 km, although an aligned pair of similar point-to-point transceiver setups may approach 10 km over a clear path. In addition, certain improved WokFi antennas, and antennas made using surplus 2-foot to 3-foot diameter round or oval satellite TV dishes, allow even far greater range, up to 20 km.

  • I think you may have confused what the OP is asking for. Your recommendation is for a product that measures distance to a target. The OP wants to transmit data between two points. Also, the idea of pointing two handheld laser devices at one another for communication is a little impractical. – Andy Oct 7 '15 at 12:33
  • They send and receive laser pulses; from the detail of the question i'd assume OP is familiar with modifying hardware. – Cees Timmerman Oct 7 '15 at 13:02
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Please read this entire site which should quickly disabuse you of the notion that the technology is simple.

The reality is that high speed laser communication (ie, slow by today's standards 10mbps) is not at all trivial, and particularly over the distances you need. There are so many tradeoffs involved in the optical path alone that you could spend months or years trying to design something that would connect at all, nevermind provide a reliable link. For instance, do you select a lower divergence, which gets more power to the end point, but means that if either end moves more than a micrometer then the connection is lost, or do you have a larger divergence which makes aiming less critical, but delivers such low power you have a hard time receiving?

That's just one of many, many trade offs and losses in the optical path engineering, and doesn't even touch the necessary low noise amplifiers and electronics, nor the physical layer interface to the network(s) or computer(s) involved in the communications. This also ignores the regulations of laser emissions in a city.

At any rate, if your requirements are

  • Laser communications
  • Up to 5km distance
  • Home budget size

Then the answer to your question, "Do they exist?" is no.

  • Please check the other answer, to me it seems quite good. Anyways, it is not clear to me, why would be the two-way communication a showstopper. "Home budget size" is not a very clear limit, and the 2-way communication only doubles the price. With other words: if a single way communication in home budget size exists, why I couldn't buy two from them for the two directions? – peterh Nov 4 '15 at 15:14
  • @peterh I've modified my answer slightly - I didn't mean to emphasize that two way communications would be much harder than one way. What I should have emphasized is that optical path losses, even on a seemingly clear day, are significant, and there are so many other issues that a cheap solution is not reasonable, and certainly doesn't exist except for the electronics and optical engineers who are counting their hundreds of hours work on this as "free". "Home budget" and "less than 5km" doesn't exist for even one way communications - unless your time is free and you are an expert. – Adam Davis Nov 4 '15 at 15:36
  • @peterh Even the ronja solution doesn't reach half that distance, and requires significant time and expertise to build. – Adam Davis Nov 4 '15 at 15:37
  • If you don't mind law and ethics, you can get a class 3B laser to distract people and sensors well over 6 km. – Cees Timmerman Nov 4 '15 at 21:56

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