is a chain of circuits one feeding into the other in order. Just as in our telephone line we have a boosting action as we proceed from coast to coast. The transmitter connects with the receiver by sending out Radio waves which the latter intercepts and passes through its various circuits. This then is strictly a case of networks, and clearly a chain network.
Now let us forget for the moment, the transmitter and consider the receiver network itself--for in Radio we have networks within networks and circuits within circuits. And at the present time we are interested chiefly in receivers. Figure 15 shows a simple, fundamental Radio circuit, of the most elementary type. Here we have nothing but an aerial, a crystal detector, a pair of headphones and a ground connection. It doesn’t look much like a closed circuit and yet it really is one as
Fig. 14
shown by the dotted line. There is no visible connection between the aerial and ground other than through the receiving apparatus, but it is there just the same or current could not flow in it. Just what this unseen connection is we shall have to leave until later.
Tracing through this circuit is a very simple matter--and for practical purposes it doesn’t matter whether we start at the ground or at the aerial. Let us, however, start with the aerial and trace the incoming signal through the circuit. The Radio wave striking the aerial becomes a very small electrical current which flows through the detector “D” where it is changed to audio frequency current, then it flows through the earphones “P” causing the diaphragm of them to vibrate and produce sounds, the same sounds that were impressed on the microphone in the transmitting station. The current flows through the phones into the ground.
