Transmitters for Telephone Handsets

Figure 2. Construction of typical telephone handset transmitters, (a. Courtesy Western Electric Co.; b. courtesy Kellogg Switchboard and Supply Co.)

Typical methods of construction are shown in Fig. 2. In each of these the diaphragm is formed and placed so that it acts as the front electrode. The other electrode is at the back of the carbon-granule cup or container. The cups are not filled entirely with granules because space must be left for expansion of the granules when the temperature rises. The diaphragm of Fig. 2(a) is cone shaped and ribbed so that it will be stiff and will move in and out somewhat like a piston. The diaphragm of Fig. 2(b) is damped acoustically so that it does not vibrate excessively at certain resonant frequencies.

A second type of handset transmitter is shown in Fig. 3(a). The diaphragm consists of two thin aluminum-alloy cones. The two electrodes are separated by paper bellows. The frequency-response curve is shown in Fig. 3(b).

Figure 3. Construction (a) and frequency response (b) of a typical telephone handset transmitter. For the meaning of the word bar, see Fig. 9. (Courtesy Automatic Electric Co.)

The telephone transmitters of Figs. 2 and 3 are known as "capsule types" because they are made as a unit and cannot be adjusted in the field. The characteristics of the handset telephone transmitters are superior to those of the transmitter of Fig. 1.