Text 5.

TUNING

A receiving circuit consisting only of an aerial with a crystal detector connected between it and the earth would not be of much

use in actual practice. It is necessary in the first place to introduce some means of vary­ing the oscillation constant of the aerial circuit in order to place it in resonance with the frequency of any particular transmitting station with which it may be desired to communicate. The natural frequency of an aerial depends on its size and shape, which determines its capacity and inductance. A de­crease in its capacity may be effected by placing another capacity in series with it. Whereas its inductance cannot be conveniently decreased, it may be increased by adding induct­ance in series. Thus, by placing a variable

inductance and a variable condenser in series with the aerial all the necessary means for either increasing or decreasing the oscillation constant within certain limits are provided. Fig. 2 shows such a circuit, A represents the aerial, С a variable condenser, L a variable inductance, D the crystal detector, T the telephone, and E the earth.