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'] Analog signaling'
2004\06\25@164021 by John N. Power

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Something like this was proposed in the early days of the telegraph as a way
to send multiple signals on a single wire. It was called the "harmonic telegraph"
but I can't remember the inventor (Morse?, Bell?, someone in Europe?).

In the very early days of radio controlled models (the vaccum tube days),
something similar was used for multi-channel control. The audio output from
the receiver was sent to an electromagnet mounted under a metal comb
formed from spring steel. The teeth decreased in length across the comb,
much like the "harp" found in music boxes. Each reed had a different
resonant frequency; on the end of each was a contact which would touch
a fixed contact below it. The vibratory signal from each contact was filtered
and discriminated to make an on-off signal for each reed.

John Power

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