Infrared LED communication question

THE_RB said:

I presented it in post #8; use a tuned circuit on the receiver at the 38kHz or whatever the transmitted freq is. Ambient light will have little to no natural 38kHz component.

The receiver problems have all been solved in RF designs, where they need to detect much smaller signals.

These days with a micro on the receiver it gets even easier, you can easily do precision DFT etc on the signal to give massive noise rejection of all frequencies but the xtal-locked freq of the transmitter.

I'd just hook up a small array of 20W of IR leds, point it roughly in the right direction, and pick it up 1km away with no problems at all.

See this page;
http://modulatedlight.org/optical_comms/optical_index.html
"Left: A 3-watt red Luxeon LED at a distance of 14.91 miles (23.85 km) with downtown Salt Lake City in the foreground.
Right: Transmitting with a 50+ watt LED with the light from the 95 mile (152km) distant end being visible at the terminus of the red beam."

1km is nothing. The world record for LED comms is 173 miles.

Click to expand...

Great links thanks, I am absolutely stunned at the distances you can get, partly I think because people have say a 1W Led torch, it's bright but hardly going to blind any passing passenger jets!
You then think of IR as being less powerful/bright, but I guess thats because you cant see it, I was talking to dad about the farm and the laser thing, apparently it was for marking the high point and the in cab system could be set to alter the gradient equipment so the field was prepared dead flat, the reason was irrigation channel flooding for watering.
Anyway when we got it, the system was a pretty new concept fr farming, hence why it wasnt so great.
But we were then talking about the security system we had, dad bred and raised many wild and endangered birds, he had alot of raptors that were worth a huge amount of money. Our security system was pretty expensive and a bit of a pain, but we had IR camera's everywhere.
What I didnt know until last night was the IR bulbs were only around 3W each! And yet even though we lived on the edge of Dartmoor and it was pitch black at night, the camera's made it look like daytime.
So in some way's it dosnt surprise me how far IR will travel, if I think about the security camera's and the tiny IR Leds on the rifle scopes. Which ever way you look at it, for the cost it has to be worth a shot!
IR Leds are pretty cheap!