French radio amateurs bounce laser signals off a rain cloud

That Amateur Radio is a hobby with variety and challenge was illustrated this week when two French radio amateurs made a one way contact over a distance of 40 km scattering laser signals from rain clouds.

The flash pulses were at times 12 dB above the noise at 40 km which seem to indicate that under the right conditions a distance of 150 km could be covered.

Laser communication systems are wireless connections through the atmosphere. They work similarly to fibre optic links, except that the beam is transmitted through free space. While generally speaking the transmitter and receiver must require line-of-sight conditions, they have the benefit of eliminating the need for broadcast rights and buried cables. Laser communication systems can be easily deployed since they are inexpensive, small, low power and do not require any radio interference studies. The carrier used for the transmission signal is typically generated by a laser diode. Two parallel beams are needed, one for transmission and one for reception.

Laser communication have been a hot topic lately, as solutions for how to satisfy ever increasing bandwidth needs are in high demand. Some have suggested that bandwidth could be distributed in neighbourhoods by putting laser communication systems on top of homes and pointing them towards a common transceiver with a fast link to the Internet. With possible transmit speeds of up to a gigabit per second, this is an exciting area.

Other applications for this technology include temporary connectivity needs (e.g. sporting events, disaster scenes, or conventions), or space based communications.

The French team proved that laser signals can be scattered from clouds thus proving that the notion that laser communication can only be line of sight, is wrong.

Source: The South African Radio League

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