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→LED beacon
== LED beacon ==
== LED beacon ==
[[File:OpComms_LED_Transmitter_diodes.jpg|frame|300px|right|The LED transmitter used high-powered red diodes, focused with small Fresnel lenses]]
The group’s first transmitter design featured nine individual red LED emitters mounted in a square matrix, each independently focused by a small Fresnel lens [https://en.wikipedia.org/wiki/Fresnel_lens]. The inherent risk in this system was lack of collimation [https://en.wikipedia.org/wiki/Collimated_light] between sources, which would lead to excessive beam divergence, and distribution of power over a large area. The team managed to mitigate this issue with precise machining tolerances that maintained the lenses at fairly accurate right angles to the intended direction of transmission. The resulting transmitter acted as a very bright red spotlight, easily visible at long distances. With this transmitter, the group was able to achieve an optical link across a distance of approximately 500 meters. This alignment was done entirely manually, with the use of tripods for stabilization. The beacon was also used in later 10km tests to provide a visual identifier to locate the receive team in the dark. This often involved having a team member manually pulse the LEDs on and off. There have been proposals to build some electronics to automatically pulse at some specified rate, but nothing has yet been built.
The group’s first transmitter design featured nine individual red LED emitters mounted in a square matrix, each independently focused by a small Fresnel lens [https://en.wikipedia.org/wiki/Fresnel_lens]. The inherent risk in this system was lack of collimation [https://en.wikipedia.org/wiki/Collimated_light] between sources, which would lead to excessive beam divergence, and distribution of power over a large area. The team managed to mitigate this issue with precise machining tolerances that maintained the lenses at fairly accurate right angles to the intended direction of transmission. The resulting transmitter acted as a very bright red spotlight, easily visible at long distances. With this transmitter, the group was able to achieve an optical link across a distance of approximately 500 meters. This alignment was done entirely manually, with the use of tripods for stabilization. The beacon was also used in later 10km tests to provide a visual identifier to locate the receive team in the dark. This often involved having a team member manually pulse the LEDs on and off. There have been proposals to build some electronics to automatically pulse at some specified rate, but nothing has yet been built.