[Laser] 104 mile/ 167 km optical comms DX record in Australia.

[Chris L]

Dear laser people,

Just a few lines to let you know that on Saturday 19 February 2005, Mike 
VK7MJ and I set an Australian optical comms DX record between Mount Barrow 
and Mount Wellington in Tasmania, a distance of 104 miles or 167 km - and we 
did it without the uage of laser sources!

The light sources used were amplitude modulated 630 nM 1 watt Luxeon LEDs, 
collimated through 20cm by 25 cm fresnels. Receivers used BPW34 PIN 
photodiode into a low noise, FET-input transimpedance preamp. Full details, 
photos of equipment, audio grabs of the contact and pics of past equipment 
are at:

http://reast.asn.au/optical.php

We are principally interested in developing NON-laser systems for long range 
use as, going by the strict letter of the law, they require no licensing and 
therefore are usable by a much broader section of the community than are 
laser-based systems. Some aspects of our optical design are novel, such as 
the usage of a secondary plano-convex lens between light source and fresnel 
to optically vary the effective size of the source, in order to fill the 
fresnel's rather fuzzy prime focus area without increasing beam dispersal 
excessively.

Aiming is via rifle sights, and the optical unit operates by bonding two 
co-lined fresnels to a single protective cover-glass sheet. Full duplex 
operation is provided.

We'd welcome any correspondence on the subject...!

Best wishes to all,

Chris Long (for Mike VK7MJ, Joe VK7JG and Jason Reilly VK7ZJA).