Man's physical universe

xanabras

RADIO GENERATION AND RECEPTION 533

The older radio sets required batteries for their operation, because

of the necessity for a direct current. The direct current is now produced

from alternating currents by the use of rectifier tubes, as mentioned

in Section 5 of this Unit. A transformer is used to step down

the voltage of the current for the filament.

The Klystron Will Produce Ultrashort Radio Waves with Considerable

Power.

Short-wave broadcasting is of advantage because less energy is

required in broadcasting, inasmuch as the waves can be focused. As a

result of focusing the waves, secrecy is made possible. Short waves

also make blind landings of airplanes more practicable. More broadcasting

stations are possible because the number of frequencies is

greater for a given broadcast range.

broadcast in

Thirty thousand stations could

the range between 9 and 10 centimeters without interfering

with each other. This is of especial value in television, inasmuch

as no television station can broadcast beyond the horizon.

The ordinary triode radio tube is not capable of delivering ultrashort

waves, partly because ultrashort waves which complete a cycle

in

1/1,000,000,000 of a second do not give enough time for electrons

to pass from the negative plate to the positive plate between changes

in plate voltage.

W. W. Hansen developed the Klystron, which consists of two

rumbatrons. The principle of the rumbatron is that pulsations are

produced by changing the velocity of a stream of electrons, rather

than by shutting off and on a current of electrons. The Klystron produces

ultrashort waves which are as ef^cient as long radio waves and

thus makes possible important advances in short-wave radio broadcasting.

Already ultrashort waves have been employed successfully to relay

television programs, thus making possible television network systems.

In 1940 the Klystron tube was used to demonstrate the transmission

of power in which members of an audience held flashlight

bulbs that were lighted by short waves transmitted from a Klystron

tube located on the platform of an auditorium. It is interesting to

note that these short waves, unlike ordinary radio waves, do not penetrate

nonmetallic materials such as wood.

Loud-speakers and Microphones Added Much to Radio Broadcasting

and Reception.

Less distortion and greater volume of sound are obtained with the

use of loud-speakers than were obtained with telephone receivers.

In

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