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Fred points out this schematic for a rather interesting radiotelephone transmitter instantaneously powered by the operator’s voice –

One of the neatest minimalist amateur radio transmitter circuits around – this one is voice powered – it provides DSB, (double side band)modulation and power from an ordinary 8-ohm speaker – if are in doubt that the circuit works, the maker has the contacts and the voice recordings to prove it!

An explanation of how it works + schematic and audio sample can be found on the El Silbo page.