Radio receiver

“ Every time a signal reaches the receiving station the current in the telephone receiver is sudden reduced; and in the time between signals the leak across the grid condenser brings the tube back to a condition where it can receive the next signal. While the sending key is depressed the current in the receiver is decreasing and increasing once for every signal which is being transmitted. For each decrease and increase in current the diaphragm of the telephone receiver makes one vibration. ”

“ Don unwrapped something that looked like a flat cigarette case with two appendages, one a disk of perforated hard rubber the size of a half dollar, and the other a three-quarter-inch-wide ribbon of opaque plastic. "I've got it, sir."
"Good. What you see is a highly advanced radio transmitter and receiver. You can imagine its value in the field. It's a pilot model you were bringing back from the contractor for tests here. ”

“ What you will have to look out for, therefore, in a receiving set is that it does not cut out some of the high notes which are necessary to give the sound its naturalness. You will also have to make sure that your apparatus does not distort, that is, does not receive and reproduce some notes or “voice frequencies” more efficiently than it does some others which are equally necessary. For that reason when you buy a transformer or a telephone receiver it is 166well to ask for a characteristic curve of the apparatus which will show how the action varies as the frequency of the current is varied. ”

“ By keying the transmitter tube, meters in the receiver tube were made to read in accordance. Then they had another conclave.
"Nothing brilliant," said Jim. "We could use super-output voice amplifiers and yell halfway across the planet if we didn't have radio. We can radio far better than this cockeyed system of signaling." ”

“ I made a crystal receiver and was able to hear the Greek Royal Navy station at Votanikos SXA and the old station at Thiseon in Athens itself, which was still a spark station. There just was nothing else to hear. I acquired a Philips 'E' type valve and built a grid-leak detector circuit, but all I got was silence. The four volt heater drew one amp and I had been trying to get it going with a small torch battery. As I became more experienced I began repairing simple broadcast receivers for my friends and putting up wire antennas for reception for people who had bought broadcast receivers. ”

“ If a telephone-receiver diaphragm can be made to vibrate in accordance with the variations in signal intensity then the air adjacent to that diaphragm will be set into vibration and these vibrations will be just like those which the human voice set up in the air molecules near the mouth of the speaker. All the different systems of receiving radio-telephone signals are merely different methods of getting a current which will affect the telephone receiver in conformity with the variations in signal strength. ”

“ Mirrors, or adding machines? You can't make an audio amplifier of a three million gain."
"I know it—at least not a practical one. But, we can probably use our audio modulator to modulate a radio frequency, and then modulate the driver with the RF. Then we hang a receiver on to the detector gadget here, and collect RF, modulated, just like a standard radio transmission, and amplify it at RF, convert it to IF, and detect it to AF. Catch?" ”

“ We'll try to contact phone stations wherever possible for this program we have in mind. Most of the stuff will be put on tape, and Dad will probably want you to prepare typed copies, too. You can do enough to take a big load off the rest of us."
"I'll be happy to try."
They spent the rest of the day in the radio room of the science shack. Ken taught Maria the simple operations of turning on the transmitter and receiver, of handling the tuning controls, and the proper procedure for making and receiving calls. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ An LRS team that can see everything and report nothing is useless. LRSUs normally use high-frequent radios to report information and receive instructions. Because of the complex nature of using the HF radio spectrum, a LRSU radio operator must have an in-depth knowledge of radios, antennas, and radio wave propagation.
D-1. HIGH-FREQUENCY RADIO FUNDAMENTALS For successful communication, HF radio performance depends on the type of emission (voice or burst device) , transmitter power output, and type of antenna. The challenge facing HF radio operators is tremendous. ”

“ A wireless telegraph transmitter is less costly than a wireless telephone transmitter and it is a very good scheme for you to learn to send and receive telegraphic messages.
At the present time, however, there are fifteen amateur receiving stations in the United States to every sending station, so you can see that the majority of wireless folks care more for listening in to the broadcasting of news and music than to sending out messages on their own account. The easiest way to begin wireless, then, is to put up an aerial and hook up a receiving set to it. ”

“ 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. ”

“ 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. ”

“ The lack of know-how and equipment may keep many from the air, but only a tiny fraction of those with resources and intelligence can hope to communicate by radio at the same time if intelligible communication is to be had, even if the entire radio spectrum is utilized in the present state of commercially acceptable technology. ”

“ The radio-telephone does not transmit the human voice. It reproduces near the ears of the listener similar motions of the air molecules and hence causes in the ears of the listener the same sensations of sound as if he were listening directly to the speaker. This reproduction takes place almost instantaneously so great is the speed with which the electrical effects travel outward from the sending antenna. If you wish to understand radio-telephony you must know something of the mechanism by which the voice is produced and something of the peculiar or characteristic properties of voice sounds. ”

“ CHAPTER THREE THE RADIO AMATEUR MOVEMENT From the turn of the century enthusiastic young men who built their own items of electrical and wireless apparatus were known as "Wireless Experimenters". Many of them were later granted licences for the use of "Wireless Telegraphy for experimental purposes" (in the United Kingdom) by the Postmaster General under the terms of the 1904 Wireless Telegraphy Act. ”

“ Although a war invention, its peacetime service will be to save lives. It is a very simple matter to rig up a wireless-telegraph system that will send messages to a considerable distance, and simpler still to rig up a receiving-set. European governments have always discouraged amateur radiotelegraphy, but in this country restrictions used to be so slight that almost any one could set up and use a radio set, both for receiving and for transmitting. ”

“ The aerial wire is precisely the same for either wireless telegraphy or wireless telephony. The transmitter of a wireless telegraph set generally uses a spark gap for setting up the electric oscillations, while usually for wireless telephony a vacuum tube is employed for this purpose. The receptor for wireless telegraphy and telephony is the same and may include either a crystal detector or a vacuum tube detector, as will be explained presently. ”

“ Tom wanted to know.
"Because, up to the present, no way has been found of utilizing in radio telephony the entire energy of the electric waves sent out," replied Professor Chadwick. "Only the variations in the waves can be detected, or transformed into sound at the receiving end of a radio telephone system. Therefore an immense amount of electrical energy has to be manufactured in order that the voice vibrations may register their variations as powerfully as possible." ”

“ Popularly speaking, it may be said that the transmitter takes the varying sounds of the human voice, and passes them on to the telephone wire, to be borne along thereon by the undulatory electric current until they reach the receiver, which takes and passes them to the human ear. ”

“ 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. ”

“ The range of intermediate wave receptors is such that they will receive amateur, broadcasting, ship and shore Navy, commercial, Arlington's time and all other stations using spark telegraph damped waves or arc or vacuum tube telephone continuous waves but not continuous wave telegraph signals, unless these have been broken up into groups at the transmitting station. ”

“ Transceivers are light weight units capable of operation with or without headsets. Each transceiver has a removeable, rechargable battery, capable of seven hours of operation based upon 10% transmitter operation, 10% receive and 80% standby operation. External, heliflex antennas are located at the top of each transceiver. There are two types of portable transceivers. The aluminum faced Type 1 transceivers are stored in the control center and will react to the Radio Net Override signal generated by either the LCCFC, ALOC or an operational PTS control trailer. ”

“ 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. ”

“ Don't--no never--connect one side of the spark gap to the aerial wire and the other side of the spark gap to the ground. The Government won't have it--that's all.
Don't try to tune your transmitter to send out waves of given length by guesswork. Use a wavemeter.
Don't use hard fiber for panels. It is a very poor insulator where high frequency currents are used.
Don't think you are the only one who doesn't know all about wireless. Wireless is a very complex art and there are many things that those experienced have still to learn. ”

“ 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. ”

“ Electromechanical protection circuits ensure that a transmitter can only be connected to an antenna that is tuned to the same frequency. The change of antennas and transmitting frequencies is made during the ten-minute interval between programmes, which always begin on the hour, preceded by the now familiar signature tune of a shepherd playing his flute with the tinkling of sheep-bells in the background, recorded in 1936, followed by the Greek National Anthem. ”