Wireless Telegraphy and Telephony/Chapter 5

by Walter W. Massie and Charles R. Underhill

 

Chapter V

Historical

18. Early Attempts

Attempts to establish communication electrically through a natural medium (that is, without the use of a wire connecting the stations) were made in the beginning of the nineteenth century.

Some inventors worked on the principle of the conducting power of the earth, and others upon the principle of electrostatic or electromagnetic induction. Of these latter types the Phelps and Edison systems were devised with a view of telegraphing to moving trains, while the Preece system was employed to communicate between an island and the mainland, utilizing both of the above principles.

The vertical aerial wire was first employed by Dolbear in 1886 in connection with a peculiar conduction system. Mr. Edison in 1891 proposed to support vertical wires by captive baloons, in connection with an induction telegraph.

Thus it is seen that the antenna (or vertical wire, as it was then called) was proposed before the principle of the real wireless telegraph was discovered, as the following retrospect will show.

Fig. 20.—Wireless Operator’s Desk, Signal Corps U. S. A.

19. Development of Wireless

Although Clerk-Maxwell proved the electromagnetic theory of light, mathematically, in 1864, it was not experimentally demonstrated that electric waves exist in free ether until 1888, when this great discovery was made by Professor Hertz.

The apparatus used by Professor Hertz, to generate the high-frequency oscillations, was, naturally, a simplified form of the generating apparatus of to-day, but without any antenna or ground connections. For a detector he employed a loop of wire with the ends nearly touching one another. When the generator, or “oscillator,” was set in operation, and the loop of wire was held near it, minute electric sparks were seen to pass between the ends of the wire constituting the loop, and the existence of the free ether waves was thus proved.

So great a discovery naturally set scientists, the world over, to experimenting, and in 1890 Dr. Branly discovered that loose metal filings, which normally have a high resistance, become fairly good conductors of electricity in the presence of electric oscillations. Dr. Branly demonstrated this by placing the filings between metal plugs in a glass tube, the device (which he called a Radio-Conductor) being connected in circuit with a battery and electric indicator. Professor Lodge called the Branly device a Coherer, and as it was found to be more sensitive than the Hertz detector, Professor Lodge combined the Hertz oscillator with the coherer in 1894, this forming the first complete wireless set.

In 1895 Count Popoff attached a vertical wire to one side of the coherer of the Lodge receiver, and connected

Fig. 21.—Interior of Experimental Wireless Station.

the other side to the ground. This device was used in meteorological work to detect the approach of thunderstorms. He was, therefore, the first to use an antenna in connection with the real wireless telegraph. Having thus increased the working range of the receiver, it only remained to connect an antenna to the transmitter; this was done by Marconi in 1896. Since that time improvements have been made in the transmitting and receiving devices, and the distances of communication have been increased from a few hundred feet to several thousand miles.

The development of very sensitive detectors has had much to do with the progress of wireless telegraphy. The Fessenden electrolytic detector is, probably, the most efficient type.

Nikola Tesla has rendered important service in the development of high-frequency apparatus, and is now experimenting with a system to transmit power without the use of wires.