Posted by: GW7AAV | October 26, 2009

Talking it up – 100 miles by voice

Michael.J.Rainey AA1TJ is a QRP enthusiast that has built what could be described as the greenest radio transmitter on the planet. His ‘El Silbo’ project is a double-sideband (DSB) transmitter is powered entirely by the energy produced by the operator’s voice. He has completed three QSO’s with a best DX of 100 miles using the device, which puts out between 5 to 15mW. The circuit is essentially a high-level DSB modulator/crystal-controlled RF oscillator.

El Silbo apparently takes its name from Silbo, which is a sort of a whistled language that’s used on the isle of La Gomera (Canary Islands) to communicate across wide mountain valleys. The best DX is apparently 2 miles, or just over 3km.

Roger G3XBM points out that this sort of thing has been done before with a 1955 article from Time magazine. The item tells how the Army Signal Corps has developed a radio transmitter that needs no energy except electricity generated by the speaker’s voice. The inventor, George Bryan managed to transmit 600 feet with a device small enough to fit in a telephone mouthpiece but suggested a range of a mile was possible.

Roger says over at his blog that Michael is also working on a receiver that uses RF harvesting techniques, which if I am correct means taking the received RF from a high-powered broadcast station and using it to drive the amplification stages in an amateur radio receiver.
Maybe it is just me but I feel these ideas may lend themselves to the development of future innovations such as an RF powered watch or as a way to power nano-technology. Just imagine tiny robots powered by RF from a BBC radio one or how about a receiver in your car powered by the noise from the engine. The only limitation is our imagination.

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