Radio Principles

Dr. Albert Einstein discards the theory of the ether usually presented by writers in an attempt to explain radio transmission. Dr. Einstein derides radio's ethereal medium as fiction, calling it a makeshift fabricated to explain* something for which scientists have not had the correct explanation. Einstein believes it is an electro-magnetic phenomenon; so did Charles Proteus Steinmetz.

Shortly before his death Steinmetzsaid: "There are no ether waves." He explained that radio and light waves are merely properties of an alternating electro-magnetic field of force which extends through space. Scientists, he contended, need no idea of ether. They can think better in the terms of electro-magnetic waves.

If a coil of insulated wire surround a piece of soft iron and a direct current be sent through the coil, it is called an electromagnet. The space around the coil is the magnetic field. When the current is increased the magnetic field increasès. When the current is decreased the breadth of the field is reduced. If the current be reversed, the field is reversed. When an alternating current is sent through the coil the magnetic field alternates. The field becomes a periodic phenomenon or a wave, described by Steinmetz as "an alternating magnetic field wave."

Steinmetz, like Einstein, pointed out that the conception of the ether is one of those hypotheses made in an attempt to explain some scientific difficulty. He declared that the more study is applied to the ether theory the more unreasonable arid untenable it becomes. He held it to be merely conservatism or lack of courage which has kept science from abandoning the ethereal hypothesis,

Steinmetz called attention to the feet that belief in an ether is in con-« tradiction to the relativity theory of Einstein, since this theory holds that ^here is no absolute position or motion, but that all positions and motions are relative and equivalent. Thus, if science agreed that the theory of relativity is correct the ether theory must be abandoned.

No space will be wasted here in talking about ether waves. The space surrounding a wire that carries an electric current is an electro-magnetic field, that is, a combination of a magnetic field and an electrostatic field.

_ If the current and voltage alternate, the electro-magnetic field alternates; that is, it is a periodic field or an electro-magnetic wave. Thus, the broadcast listener who wants to forget the ether can think of the aerial wire at the transmitter, setting up electro-magnetic waves in a field of electric force, which now, the theories contend, fills all space and therefore every receiving "wire is within the field. This field, however, is supposed to be in a state of rest until the broadcast transmitter causes it to vibrate.

The action of the transmitter is like tapping a. mold of jello. leaves pass through it, and so radio waves are produced in the electro-magnetic field.

The transmitter taps the hypothetical medium, causing it to vibrate. The receiving set is designed to detect the vibrations and so intelligence is carried from one point to another.

It is well known that a stone thrown into a pond causes ripples or waves on the surface of the water, which move away

NOTE.—As stated Or. tee de Foresti Radio is simply a cause and an effect. The consols the radio transmitter. It makes an electro-magnetic splash that sets up radio waves. ThesdrWaves travel through space in all directions. The effect is the setting up of delicate currents in the aerial or loop. These delicate currents are detected and converted into audible sounds by means of the radio receiving set. Imagine a boy operating a paddle at one end of a pond of still water. Ripples are set up in the water. They travel farther and farther away from the paddle, getting weaker as they move along until they reach a piece of wood which bobs up and down as it rides the waves. Put a bell on the piece of wood, in order that it will ring with the action of the waves, this illustrates the mechanical parallel of radio communication. >

from the point of disturbance in concentric circles of ever increasing diameters until they reach the shore. The number of waves breaking on the shore in one second is called the frequency of the wave motion, and the distance between them measured from crest to crest, is the wave length.

The waves are strongest at the point of disturbance and gradually become weaker as they travel away from that point, as shown in figs. 1 and 2. If the distance be sufficiently great they will become so weak as to be invisible.

point of disturbance" waves

Fig. 1.—Effect of throwing stone in still water; production of waves which radiate or travel from the point where stone enters the water, or "point of disturbance."

point of disturbance" waves

Fig. 1.—Effect of throwing stone in still water; production of waves which radiate or travel from the point where stone enters the water, or "point of disturbance."

NOTE.—According to Marconi radio wanes go to outer space. In his inaugural address at the second meeting of the Italian Society for the Advancement of Science Sept. 11,1930, Sen. Guglielmo Marconi expressed belief that radio waves may travel long distances, even ribbons -of miles, beyond the earth's atmospheric layer. He said that he did not see any reason why, as some scientists maintain, waves produced on the earth should not travel such a distance, since light and heat waves reach the earth from the sun, penetrating the atmospheric layer. He referred to observations of such scientists as Stormer and Pedersen and commented that the former had said that electrified particles derived from the sun and under the magnetic influence of the earth acted as a reflector of electric waves from the earth after they had passed the sa called Keoelly-Heaviside layer.

Radio communication as has been explained is a form of wave motion which occurs in an electro-magnetic field, these waves acting in a similar manner to water waves.

In radio communication it is first necessary to create electromagnetic waves in varying groups and of varying strength, and second to intercept them with apparatus capable of changing them to sound waves.

To create the waves it is necessary to have two surfaces separated, by a distance of from ten to several hundred feet and to create between them an electrical pressure which changes its direction (first toward one surface then toward the other) hundreds of thousands of times a second.

Fig, 2 —Sectional view of waves produced by throwing stone in still water» illustrating crest of wave, wave length and gradual weakening of the waves as they travel from the point of disturbance.

Jt is the common practice to use the ground for one surface and provide another surface by erecting a structure composed of one or more wires, insulated from the earth and suspended many feet above it.

Between these, by means of suitable transmitting equipment an electrical pressure is produced of from one to twenty volts which starts waves radiating out in all directions. These pressure waves are, however, only part of a radio wave. From any wire in, which current is flowing are radiated electro-magnetic waves and radio waves are made up then, of both electro-magnetic and pressure electrostatic waves.

Comparing these waves to the action of hurling a rock into a pool of water, the amperes of electric current put into the antenna correspond to the size of the rock, while the volts of electrical pressure are equivalent to" the force with which the rock is hurled. The larger the rock and the greater the force behind it, the bigger the splash and consequent waves. The more amperes of current flowing in the antenna circuit and the greater the pressure (volts) between antenna and, ground, the stronger the waves radiated. These radio waves have similar characteristics to Another class of waves—sound waves. •

When the note C is struck on the piano (as in fig. '3 ) the sound waves vibrate 256 times per second and either a C tuning for1: or a Wire tuned to C and in the immediate vicinity will vibrate 256 times per second also. The two wires are said to be in resonance.

RESONANCE-

'256 waves per sec.

sympathetic vibration ofu tuning) fork (in unison) ) } v------ -»—'

sympathetic vibration ofu tuning) fork (in unison) ) } v------ -»—'

r Fig. 3.—Sympathetic vibration of tuning fork with struck piano string when tuned to same pitch, illustrating the wave theory of radio.

The waves radiated by a radio transmitter always have a definite number per second and in order to hear a station, the receiving equipment must be put in resonance with the waves radiated by the. transmitter. This operation is known as tuning,

BROADCASTING PRINCIPLES

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Vibration of vocal cords of speaker (1) producing soufrd, causes air to vibrate in front of mouth (2) which in turn causes the thin diaphragm of microphone (3) to vibrate. The microphone changes the mechanical vibrations to varied electric currents (4); an amplifier (5) amplifies these currents as at (6). An oscillator, or radio wave producing, device (7), in the meantime, produces radio waves (9) for broadcasting. A modulator (8) modulates or changes these radio waves to travel as sound waves. The varied currents (6) enter the modulator (8) and cause the radio waves (9J to flow out as at (10), conforming to the electric sound waves. An amplifier(ll) amplifies the modulated radio waves, to give them more power, as at (12); these waves enter the antenna (13) and travel out into space as at (14)— going in all directions ready to be picked up by receiving antennas.

CHAPTER 2

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