Notice that current must flow through each part of the circuit--if there were a break in any point in this circuit the current could not flow. Therefore it is a series circuit--the detector and earphones are in series with the antenna and ground.
Figure 16 shows the same circuit but has included in it a turning coil, marked “L” which acts as a station selector. Of course these very simple circuits are not efficient--they won’t pick up signals from stations more than a few miles away. The untuned circuit shown in Fig. 15 will respond to signals of several stations if equally powerful and at an equal distance from the receiver. The circuit in Fig. 16 can be tuned, but only to nearby powerful stations.
When we come to Fig. 17 we have what should properly be
Fig. 15
Fig. 16
Fig. 17
Fig. 18
called a receiving network, for here we have two circuits. In the antenna circuit there is a coil in series with the aerial and ground. The other circuit is a series-parallel circuit--notice the crystal detector “D” and the earphones “Ph” in series. In this circuit the source of supply is “S,” a coil. The two coils marked “P” and “S” are the primary and secondary of a transformer by means of which energy is passed on from the aerial circuit to the second circuit. Just how energy can be passed from one coil to another is another matter which we must leave until later. For the present, however, we must consider “S” as the source of supply in he second circuit. The load in the circuit consists of the detector and the phones. The variable condenser, in parallel the “S” is a tuning device. It regulates current flow as would a resistance, in that it adjusts its
