Man's physical universe

xanabras

;

RADIO GENERATION AND RECEPTION 529

Marconi Invented the Wireless Telegraph.

Hertz considered the possibility of using these "wireless" waves for

communication but he could not devise a method to detect the wave

^

at a distance. Discoveries of other men furnished the basis for wireless

wave reception, but it remained

^

first

for Marconi to work out its

use in actual communication.

Guglielmo Marconi (1874- )

improved the sending apparatus

so as to give waves of greater intensity.

The plates of the condenser

had to be enlarged, and

Marconi conceived the idea of

using a system of wires (or antennae)

supported high in the air

as one plate of the condenser and

tc

^B

"r

iiiiiiiiiit

the ground as the other plate.

A high-frequency induction coil

operated by a battery produced Fig. 259. Marconi's sending apparatus

: A, antenna ; B, induction coil

the current, and the signals were

C, spark gap ; D, key ; E, battery

produced by making and breaking

the current with a telegraph

G, ground.

key. The spark was produced between two wires, one leading from the

ground and the other leading from the antennae. The spark produced

the electromagnetic waves (now called Hertzian or radio waves) , which

were detected by the receiving set.

The oscillations in the receiving circuit are very feeble, but their

effective reception has been greatly increased by the use of antennae.

Marconi used a coherer tube as a detector. The principle of the coherer

had been worked out by other investigators, but they did not realize

its possibilities. The principle is simple; a tube of nonconducting

material, such as glass, is filled with metal particles. When the particles

are subjected to electromagnetic waves, they cohere and thus

increase the ability of the particles to conduct a current. Marconi

used an electric tapper to cause the particles to decohere after each

impulse. A current was thus caused to operate a telegraphic sounder

so that Morse signals could be received.

An early form of detector consisted of a crystal of galena in contact

with a piece of copper wire. Such a crystal permitted the current to

pass more readily in one direction than in the opposite direction and

thus converted the oscillations into impulses in one direction which

could be detected by a telephone receiver. Perhaps some of the

E

More magazines by this user
Similar magazines