Tonewheel
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A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric musical notes in electromechanical organ instruments such as the Hammond organ and in telephony to genera
Goldschmidt tone wheel (1910), used as an early beat frequency oscillator
Rheotome-cylinders and electric-brushes used on Telharmonium (1896)
Beat frequency oscillator
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In a radio receiver, a beat frequency oscillator or BFO is a dedicated oscillator used to create an audio frequency signal from Morse code radiotelegraphy transmissions to make them audible. The signa
Tonewheel
…for the telharmonium c. 1896 and patented in 1897. It was reinvented around 1910 by Rudolph Goldschmidt for use in pre–vacuum-tube radio receivers as a beat frequency oscillator (BFO) to make continuous wave radiotelegraphy (Morse code) signals audible. The tonewheel assembly consists of a synchronous AC motor and an associated…
455 kHz BFO unit for SSB reception
Separate BFO oscillators were manufactured for receivers that didn't have them; a Rohde und Schwarz STI4032 from 1944.