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BASIC OF TELEPHONE
2.1
Transmitter (Microphone)
The voice vibrates a diaphragm compressing/releasing carbon powder.
When carbon powder is compressed, its contact resistance decreases.
When the powder is released, its contact resistance increases. So direct
current varies corresponding to the change of pressure (voice). This is
called "voice current". Recently, a microphone is applied to the transmitter
of the telephone.
1–6
Air vibration
Contact
Carbon powder
resistance
Fixed electrode
Voice current
Diaphragm
Fig. 1-6 Transmitter and Voice Current
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