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The Transmitter

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-419

2025-12-15

773

 While' the Bell receiver was originally used as a transmitter, many more efficient forms have been devised. Among these is the solid-back transmitter, shown in cross section in Fig. 1. The principle upon which this is made is that of the varying resistance of granular carbon produced by pressure upon it. The essential parts are the mouthpiece M, the metal case, the aluminum diaphragm D, the front terminal F, the back terminal B, and the granular carbon between the terminals. The terminals are connected with the primary of an induction coil in series with the line. A condensation of the sound wave entering the mouthpiece causes the diaphragm to compress the carbon granules; this reduces the resistance, and the current is increased. A rarefaction causes the diaphragm to lessen the pressure on the carbon; this increases the resistance, and reduces the current. These variations in the current respond with marvelous sensitiveness to the vibrations of the diaphragm and result in corresponding vibrations in the diaphragm of the receiving instrument, which is coupled in series with the secondary of the coil.