Being desirous of keeping this book as far as possible within the limits prescribed by the title, it is not possible to go deeply into the theory of the propagation of electric waves, but at the same time it is not deemed advisable to plunge suddenly into the construction of wireless apparatus without giving some explanation of the underlying principles.
If the reader desires information upon this subject he is referred to Fleming's "Electric Wave Telegraphy" or the same author's "Elementary Manual of Radio-telegraphy and Radio-telephony."
The explanations given in this chapter do not involve any actual theory of the transmission and reception of electric waves. They are merely intended to show the train of actions which take place and may be observed in a physical sense. With this purpose in view, several references have been made to simple hydraulic apparatus and an analogy drawn to render the explanation clearer.
The Transmission and Reception of Electric Waves.
Wireless telegraphy by means of electromagnetic waves may be divided into four distinct operations, namely:
- The generation of electrical oscillations.
- The transformation of electrical oscillations into electrical waves.
- The transformation of electrical waves into electrical oscillations.
- The detection of the electrical oscillations.
The first two operations comprise those taking place at the transmitter, while the last two, which are the converse of the first, are in evidence only when receiving.
Fig 1. Hertz Oscillator and Resonator.
Fig. 1 illustrates the original Hertz oscillator and resonator, which is the simplest form a wireless installation may take. T represents the transmitting apparatus and R the receptor. At the transmitting station a telegraph key is placed in series with a battery and an induction coil. Two large metal plates, t and t', are connected to the opposite sides of the spark gap, which in turn is connected to the secondary of the induction coil. When the key is pressed the electrical circuit is completed and the voltage of the battery is raised sufficiently by the induction coil to charge the metal plates t and t'.