Radiotelephone

“ I told him about my visitor and the repair job. "What I did was add a modulator-oscillator-power amplifier, and a few feet of wire for an antenna, coiled around inside the case."
"So what does that make it?"
"Simple. It makes it a radio transmitter. Not only will he hear what the horses are saying, but anyone in town with a radio tuned to that frequency will, too."
"And where does that get you?" The sergeant was still puzzled but not bored now. ”

“ Just the same, only in radio telephony we are confronted by a problem not met with in wireless telegraphy. We have not only to transmit sound, such as isolated dots and dashes, but to send through the air every rise and fall and inflection of the human voice just as it is recorded in the minute lines of a phonographic record. ”

“ To make wireless telephony a success it was necessary to find some way of making perfectly uniform carrier-waves, and then of loading on them waves of speech. Of course, the latter are not sound-waves, because they are not waves of air, but they are electro-magnetic waves corresponding exactly to the sound-waves of air and at the receiving-end they affect the telephone receiver in the191 same way that it is affected by the electric waves which are sent over telephone wires. ”

“ When a sub is heard and located, the listeners call the net-layers by radio, and they go to the spot at a thirty-knot speed. As they approach they soon drown out the sound of the sub, but their speed and number enables them to surround the area in which she is known to be, for she won’t have time to go far from where she was last heard. Paying out their nets, they hem her in and keep the ring of nets closed round her till the area is raked with trailing wires and other electromagnetic detectors which will enable the chasers to concentrate their depth charges with the certainty of a kill. ”

“ Truly the science of radio-telegraphy has made rapid strides since the days of the “coherer,” until now, after the war, it is the most advanced in our human civilisation, and at the same time full of romance. Not a month passes but something new is discovered in that high-built, well-knit laboratory, where daily the keenest brains of wireless experimenters are at work devising, testing, and too often scrapping new instruments, new circuits, and new devices in order to improve and render less complicated both the ordinary wireless by Morse, and that modern marvel, the wireless telephone. ”

“ You can see that very few telephone messages can be sent in the long-wave-length part of the radio range and many more, although not very many after all, in the short wave-length part of the radio range. You can also see why it is desirable to keep amateurs in the short wave-length part of the range where more of them can transmit simultaneously without interfering with each other or with commercial radio stations. ”

“ It might reasonably be asked why a telephone receiver could not be directly connected to the aerial and ground so that it would respond directly to the high frequency currents generated by the incoming waves without the medium of a detector. There are two very good reasons why such a method would not be possible, the first being that the little magnet coils contained in the telephone receivers exert a choking action upon alternating currents of high frequency which effectually blocks their passage. ”

“ A single receiver can be used but a pair of receivers connected with a head-band gives far better results. Then again the higher the resistance of the receivers the more sensitive they often are and those wound to as high a resistance as 3,200 ohms are made for use with the best sets. To make the incoming signals, conversation or music, audible to a room full of people instead of to just yourself you must use what is called a loud speaker. In its simplest form this consists of a metal cone like a megaphone to which is fitted a telephone receiver. ”

“ Nearly all the big wireless companies have great stations fitted with powerful telephone transmitters and at given hours of the day and night they send out songs by popular singers, dance music by jazz orchestras, fashion talks by and for the ladies, agricultural reports, government weather forecasts and other interesting features. Then by simply shifting the slide on your tuning coil you can often tune-in someone who is sending Morse, that is, messages in the dot and dash code, or, perhaps a friend who has a wireless telephone transmitter and is talking. ”

“ In an emergency, any wire of sufficient length can be used for an antenna; for example, barbed wire, electrical wire, fence wire, and metal-cored clothesline. Communication has been successful using metal house gutters and even metal bed springs. A radio operator's mission is not completed until communication is established. f. Grounding. A good electrical ground is needed for two reasons: first, to protect the operator and his equipment; and second, as a radio frequency ground needed by some antennas to function properly. ”

“ If the radio signal having a frequency above the critical frequency is sent at an angle, the signal is bent back to earth instead of passing through the region. This can be compared to skipping stones across a pond. If a stone is thrown straight down at the water, it penetrates the surface. If a stone is thrown at an angle to the pond, the stone skips across the pond. For every circuit, there is an optimum angle above the horizon called the takeoff angle. It produces the strongest signal at the receiving station. This optimum takeoff angle is used to select the antenna for a specific circuit. ”

“ In electric currents 100 per second is a low frequency current, 100,000 per second is spoken of as high frequency. In early experiments with radio telephony it was found that the chief difficulty lay in obtaining a current of sufficiently high frequency to transmit the human voice, the currents used in wireless telephony being much too weak for this purpose.
"I had, therefore, to invent my own alternator, which is attached to that gasoline motor. There is a similar one in the shed from which you just talked with me." ”

“ That is why any wireless receiving station, within a certain radius, can catch any messages that may be flying through the air--that is unless certain apparatus is tuned, or adjusted, to prevent this."
"Well, once the impulses, or electric currents, are sent out into space, all that is necessary to do is to break, or interrupt them at certain intervals, to make dots, dashes and spaces. These make corresponding clicks in the telephone receiver which the operator at the receiving station wears on his ear. ”

“ Maybe thar is some way, except by water, in spite of what he said."
"Maybe there is," said Jack. "It seems a shame to think of all that rich stuff lying there neglected and unobtainable."
"It does indeed," agreed the professor. "In that sample I find traces of metals from which filaments for electric lights could be made and substances invaluable in medicine for X-ray purposes as well as the Z.2.X. which your father is convinced would make the radio telephone as practical as the wireless telegraph." ”

“ In that way, a single pair of wires can be used for transmitting, simultaneously and without any interference, several different telephone conversations. It takes very much less power than would radio transmission and the conversations are secret. The ordinary telephone conversation can go on at the same time without any interference with those which are being carried by the modulations in high-frequency currents. ”

“ Bill explained. "It will be all right in the morning. If you want to listen to the radio, you can use the portable radio directional finder. That always works."
"I want to catch the 5 o'clock news and hear the latest on our satellite," Carol replied. She went to the RDF and switched it on to the standard broadcast channel. "Anyhow, I'd feel better if we could put out a signal. The way we're limping along with water in our gas is no fun. ”

“ Not by any means.”
“But radio turned the trick just the same,” said Bob slangily. “I’ve read that a message that used to take two days to pass between ranger stations can be sent now in a few seconds.”
“Right!” exclaimed Mr. Bentley, his eyes glinting. “In a little while the saving in the cost of forest fires will more than pay for the installation of radio. We nose out a fire and send word by wireless to the nearest station, before the fire fairly knows it’s started.”
“But just what is it that you do?” asked Joe, with flattering eagerness. ”

“ They’re coming into the ranks by thousands every day. Nobody can keep count of them, but they must run into the millions.
“And they’re great in quality as well as quantity,” he continued, warming to his favorite subject. “The President of the United States has a radio receiving set on his desk. There’s one in the office of every one of the ten Cabinet members. The Secretary of the Navy is sending out wireless messages every day to vessels scattered in all parts of the globe. The head of the army is keeping in touch by radio with every fort and garrison and corps area in the United States. ”

“ The minutest vibrations conveyed to the stand are perceived at the receiver as loud noises. The tread of a fly walking over the board, S, is heard like the tramp of a horse, and the ticks of a watch are audible in the receiver when the ear is several inches away from it. The slight touch of a feather on the stand is distinctly audible, and a current of air impinging upon it is reproduced as the noise of a stream of water. The microphone is, in fact, the most sensitive detector of vibrations that is known, and its employment as a transmitter has brought the telephone to its present perfection. ”

“ The reason that distant radio stations are sometimes heard better than nearby ones, is because the other waves are propagated both in an upward and an outward direction. The more or less parallel waves reach nearby stations, while those going upward are deflected downward at an angle upon reaching the upper strata, and arrive at a spot on the earth's surface far beyond the normal range of the station. Ships which are, therefore, at that particular spot at a given time are enabled to receive the signals. ”

“ In any system of radio-telephony you will always find that there is produced at the transmitting station a high-frequency alternating current and that this current flows in a tuned circuit one part of which is the condenser formed by the antenna and the ground (or something which acts like a ground) . This high-frequency current, or radio-current, as we usually say, is varied in its strength. It is varied in conformity with the human voice. If the human 147voice speaking into the transmitter is low pitched there are slow variations in the intensity of the radio current. ”

“ Components of a radio transmitter.
1017. Receivers When a radio wave passes a conductor, a current is induced in that conductor. A radio receiver is a device which senses the power thus generated in an antenna, and transforms it into usable form. It is able to select signals of a single frequency (actually a narrow band of frequencies) from among the many which may reach the receiving antenna. The receiver is able to demodulate the signal and provide adequate amplification. The output of a receiver may be presented audibly by earphones or loudspeaker ”

“ After being in radio work and seeing the opportunities there are for mistakes I have decided operators cannot be too careful. You see it is not like talking with a person face to face. Those you are communicating with are usually miles and miles away. Such stations as I have been telling you about are on the lookout for any six-hundred-meter calls and they answer in this tune. After communication with a ship is established, however, the tune shifts to seven hundred and fifty-six meters if a Navy vessel should be talking; if not, the six-hundred-meter wave length assigned is used. ”

“ And new means for modulating electric current by changing light values may be expected when the American boy starts to play with this new toy.
There has been a veritable army of engineers engaged in the development of radio as a service to the ear, while relatively few engineers have been developing radio as a service to the eye.
It is believed that the distant electric modulation of light for many purposes will soon become a common phenomena and eventually of inestimable service in science, in engineering, in industry, and in the home. ”

“ Strictly speaking, the telephone only changes sound-waves into waves of electricity and back again. When two telephones are connected by means of a wire, they act in this way,—the first telephone changes the sound-waves it receives into electric impulses which travel along the wire until they reach the second telephone, here they are changed back to sound-waves exactly like those received by the first telephone. Accordingly, the listener in New York seems to hear the very tones of his friend who is speaking at the other end of the line, say, in Boston. ”

“ Inside was a complete radio receiving set, with vacuum tube detector and batteries in perfect working order. Between the roots of the tree an 182 iron pipe had been driven into the earth to act as a ground. The antenna was strung from top to bottom of the tree on the side away from the path, and there was nothing to differentiate the box from an ordinary wire telephone set, except that it was slightly larger. ”