Abstract: 

Rex Moncur, VK7MO, and a group of radio amateurs in Tasmania have been experimenting with Over-the-Horizon Optical Communication. Distances of up to 66 km have been achieved with narrow bandwidth Digital Modes via cloudbounce propagation using banks of Light Emitting Diodes (at visible wavelengths) focused by small plastic lenses as used in torches. Extensive propagation experiments have been conducted over a distance of 27 km using a single LED at milli-Hz bandwidths to gain insights into propagation conditions.  The success of this work relies on the use of relatively wide beamwidths (10 degrees) to overcome the problems of alignment on clouds, combined with the use of new higher power (500 mW) Luxeon Light Emitting Diodes, the use of large (up to 400x400 mm) plastic Fresnel Lens to capture as much light as possible and the use of low noise receivers. Rex will talk about the development of the equipment for these experiments and recent work using Photo Multiplier Tubes and Avalanche Photo diodes.