At the top of the stand was mounted a carbon microphone ( " transmitter " ) to speak into, and a switch hook extending sideways upon which an ear piece ( " receiver " ) was hung.
42.
Carbon microphones, usually modified telephone transmitters, were widely used in early AM radio broadcasting systems, but their limited frequency response, as well as a fairly high noise level, led to their abandonment in those applications by the late 1920s.
43.
These repeaters worked by mechanically coupling a magnetic telephone receiver to a carbon microphone : the faint signal from the receiver was transferred to the microphone, where it modulated a stronger electric current, producing a stronger electrical signal to send down the line.
44.
Telephone hummer / oscillator by A . S . Hibbard in 1890 ( carbon microphone has power gain ); Larsen " used the same principle in the production of alternating current from a direct current source "; accidental development of vacuum tube oscillator; all at p . 86.
45.
In 1931, Shure and engineer Ralph Glover began development of the first Shure microphone, and the following year, the Model 33N Two-Button Carbon Microphone was introduced, making Shure one of only four microphone manufacturers in the U . S . Shure's first condenser microphone, crystal microphone, and microphone suspension support system ( for which they received their first patent ) were all introduced that same decade.
46.
Reviewing Fessenden's patent, he wrote that " The creation of an electric wave seems to involve a certain suddenness in the beginning of the oscillations, and an alternator giving a simple sine-curve would not be likely to produce the required effect . . . " ( In view of Fessenden's ultimate success, this statement disappeared from the book's 1916 edition . ) Fessenden's next step, taken from standard wire-telephone practice, was to insert a simple carbon microphone into the transmission line, which was used to modulate the carrier wave signal for audio transmissions, or, again using modern terms, used to produce amplitude modulated ( AM ) radio signals.
