Rocking armature transmitter

Carbon granule transmitter

Telephone transmitters

Telephone transmitters have been designed using numerous tech­niques to convert sound impinging onto the transmitter into electri­cal energy.

Carbon granule transmitters were very common from the earliest days of telephony until comparatively recently. The principle of operation is shown in Figure 58.2. Sound pressure impinges on the diaphragm causing it to vibrate. The centre of the diaphragm is attached to a carbon electrode which moves, compressing and decompressing the fine carbon granules sealed in the chamber at the rear of the device. A second carbon electrode is fixed to the back wall of the device. The variation in pressure on the fine carbon granules causes the resistance between the two electrodes to vary in unison with movement of the dia­phragm. When a d.c. supply is connected between the two carbon electrodes, and the carbon granules are compressed and decom­pressed, an alternating current is superimposed on the d.c. supply which represents the speech signal.

The rocking armature transmitter is shown in Figure 58.3. Sound pressure impinges on the diaphragm causing the armature to pivot, altering the magnetic field and inducing an alternating current in the coils. This alternating current represents the speech signal.

Дата добавления: 2015-03-31