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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Telephone. History of invention and production
Directory / The history of technology, technology, objects around us A telephone is an apparatus for transmitting and receiving sound (mainly human speech) at a distance.
With invention telegraph solved the problem of transmitting messages over long distances. However, the telegraph could only send written dispatches. Meanwhile, many inventors dreamed of a more perfect and communicative method of communication, with the help of which it would be possible to transmit the live sound of human speech or music over any distance. The first experiments in this direction were undertaken in 1837 by the American physicist Page. The essence of Page's experiments was very simple. He assembled an electrical circuit, which included a tuning fork, an electromagnet and galvanic cells. During its oscillations, the tuning fork quickly opened and closed the circuit. This intermittent current was transmitted to an electromagnet, which just as quickly attracted and released a thin steel rod. As a result of these vibrations, the rod produced a singing sound similar to that of a tuning fork. Thus, Page showed that it is possible in principle to transmit sound using electric current, it is only necessary to create more advanced transmitting and receiving devices.
The next important stage in the development of telephony is associated with the name of the English inventor Reiss. Even in his student years, Reis became interested in the problem of transmitting sound over a distance using electric current. By 1860, he had designed up to a dozen different devices. The most perfect of them had the following form. The transmitter was a hollow box, equipped with a sound hole A in front and having a hole in its upper part, closed by a thin, tightly stretched membrane. On this membrane lay a thin platinum plate p, and on top was the point of an elastic platinum needle n, which was adapted in such a way that it touched the plate p when the membrane was at rest. This contact was interrupted by the vibration of the membrane. As a result of these transverse touches, the current flowing from the battery B through the clamp a into the platinum plate p and through the needle n into the second clamp was closed and opened, from the latter the wire went to the receiver, passed through the coil CC and returned to the battery through the clamp d and connected to it wire e. Inside the spiral was placed a thin iron needle, which was attached with its two ends to two racks ff resting on the resonator board gg. The hi and ki parts formed contraptions at both stations, intended to let the distant listener know that negotiations had begun. The reproduction of the sound sung in trumpet A was based on the fact that an iron spoke, being magnetized and demagnetized by an electric current passing in a spiral, began to oscillate; they were felt as a sound corresponding to the sound that was perceived by the receiver and whose vibrations set the membrane in motion. The resonance board served to amplify the sound. Using Reis's phone, it was already possible to transmit not only individual sounds, but also complex musical phrases and even partly human speech. But the quality of the transmission remained so low that it was often completely impossible to make out anything. The side noises produced by the closing and opening of the circuit drowned out the transmission, and the sounds reproduced by the steel needle were very far from the modulations of the human voice. For a clear transmission of sound, it was necessary to ensure that the plates of both the sender and the receiver were driven from their rest position to the extreme position by a current, the strength of which would increase gradually, and that, when decreasing, the current would again pass through the original rest position. All these smooth fluctuations in the timbre of sound, which make up the richness of human speech, were completely inaccessible to Reis's phone - the attraction here came on rapidly and remained unchanged for some time, and then completely stopped. It turned out to be impossible to solve the problem of sound transmission only by closing and opening the circuit. Another 15 years passed before the Scottish inventor Alexander Bell found a better way to convert sounds into electrical signals. By profession, Bell was a teacher of deaf and dumb children. From childhood, he studied a lot of acoustics, the study of sound, and dreamed of inventing a telephone. In 1870 Bell moved to Canada and in 1872 to the USA. Having settled in Boston, he introduced the system of "visible speech" developed by him in the local school for deaf and dumb children. It was a great success, and Bell soon became a professor at Boston University. Now he had a laboratory and sufficient funds to devote himself to working on the invention of the telephone. Forgetting about sleep, Bell spent whole nights sitting over his experiments. His first experiments replicated Page's work. In the summer of 1875, Bell and his assistant, Thomas Watson, made an apparatus that consisted of magnets with movable tongues, which were driven by current fluctuations. Various devices were included in the circuit with magnets. Watson and Bell were in adjoining rooms. Watson transmitted and Bell received. Once, when Watson pressed the button at the end of the wire to activate the bell, the contact went bad, and the electromagnet pulled the bell hammer towards itself. Watson tried to pull it away, as a result of which vibrations arose around the magnet. The movement of the spring produced by Watson changed the intensity of the current and caused oscillatory movements in the spring of the opposite station in Bell's room, and the wire transmitted the very faint sound of the first telephone. So, quite by accident, Bell discovered that a magnet with a light anchor can be both a transmitter and a signal receiver. After that, it was no longer difficult to transmit and reproduce sound using electric current. To understand how this happens, imagine a permanent magnet and, in the vicinity of it, a flexible iron plate that vibrates under the action of sound waves. Approaching the pole of a magnet, it will strengthen its magnetic field, and moving away from it, weaken it. (Without going into details, we note that the reason for this will be the same phenomenon of electromagnetic induction, which was discussed in the previous chapter: it is clear that an electric current will arise in a plate that moves in a magnetic field; this current will create its own magnetic field around the plate field, which will be superimposed on the magnetic field of the magnet, either strengthening or weakening it.) Now let's place a coil of wire on our imaginary magnet. When the magnetic field fluctuates in the coil, an alternating electric current will occur, and then in one direction, then in the other direction. By passing the received current through the windings of another magnet, we will influence its magnetic field, which will also either increase or decrease, and exactly repeat all the changes that occur in the magnetic field of the first magnet. If an iron plate is placed at the pole of this second receiving magnet, it will either be attracted to this magnet under the action of an increasing magnetic field, then move away from it under the influence of its elasticity and at the same time generate sound waves similar in everything to those that set the first oscillation in motion. plate. Actually, this happened under the circumstances described above. The role of the iron plate here was played by the flexible armature of the magnet. But it was too crude a device, unable to convey many of the nuances of sound. Bell began to look for something to replace him. A doctor friend suggested that he use a human ear for experiments and got him an ear from a corpse. By carefully studying its structure, Bell found that sound waves vibrate the eardrum, from which they are transmitted to the auditory ossicles. This led him to the idea of making a thin metal membrane, placing it next to a permanent magnet, and thus converting sound vibrations into electrical ones. It took several months of hard work before the phone spoke. Only on March 10, 1876, Watson clearly heard Bell's words at the receiving station: "Mr. Watson, please come here, I need to talk to you." Even earlier, on February 14, Bell made a patent application for his invention. Just two hours after him, another inventor, Elisha Gray, filed the same application for an identical apparatus. However, the patent was issued in March to Bell, as he was the first to announce his discovery. (Later, Bell had to fight several lawsuits with Gray and other inventors to defend his superiority. In the end, Bell bought the right to operate the telephone from Gray.) At the Philadelphia exhibition that year, Bell's telephone became the main exhibit. Since that time, despite the fact that the first devices were still very imperfect, telephones began to spread rapidly. In August of the same 1876, there were already about 800 telephones in use, and the demand for them was increasing.
The device of the first devices was very primitive. A rod-shaped permanent magnet A was surrounded at one pole by a short inductive coil B of thin copper wire, terminated in two thicker wires CC, which were connected by clamps DD to the wires LL. At one pole of the magnet was placed a plate EE of soft sheet iron clamped along the edges. Everything was set in a wooden frame, which in part GG had a funnel-shaped hole above the EE plate, which served as a sound cone. At the bottom, the wooden frame narrowed, since here it contained only a magnetic rod, fixed in its position with a screw, and two CC wires. This device could serve as both a transmitter and a receiver. There was such a telephone at the sender's station and at the receiving station. Their induction coils were interconnected by means of LL wires and DD clamps. When the cone GG is used as a tube and spoken into it, the plate EE in front of the pole of the magnet oscillates; as a result, inductive currents arose in the spiral B, the change of which corresponded to the sound vibrations acting on the plate. These currents flowed through the LL wires into the coil of the receiving telephone and caused the membrane to vibrate. By pressing the cone to your ear, you could hear the voice of the subscriber speaking on the other end of the wire. The induction currents generated by the movement of the membrane were very weak, so stable communication could only be established at a distance of several hundred meters. Further, the voices of the speakers became so quiet that they were drowned in the hum of interference. It took the work of many, many inventors before the telephone became a reliable means of communication. In general, Bell's telephone turned out to be more capable of converting current waves into sound waves than vice versa. Therefore, the discovery of the microphone effect in 1877 by the English inventor Hughes was very important in the history of telephony. In its original form, the microphone had the following device.
Between two pieces of coal C and C', mounted on plate B, a carbon rod with pointed ends was installed. The current from element E passed through this carbon rod and through the winding of the telephone T. When the horizontal plate A, which played the role of a resonator, was shaken, the carbon rod was displaced. At this moment, its resistance to current at the points of contacts decreased, and this, in turn, produced a noticeable increase in the current strength in the telephone. The membrane began to oscillate with a larger amplitude, which caused the initial sound to be amplified several times. The faint ticking of the watch placed on the stand was perceived as very loud in the phone. Even the crawling of a fly on the plate was reproduced in the form of quite noticeable noise. Within a few years of Hughes' invention, many different microphone designs emerged. Microphones that used carbon powder instead of rods were widely used. In this case, the vibrations of the membrane caused either a compaction of the powder or its loosening, as a result of which its resistance constantly changed. The phone connected to the microphone became much more reliable, but it still remained imperfect. Weak induction currents were unable to overcome the resistance of the transmission wires. It was necessary to somehow increase their tension, without changing the nature of their vibrations. A witty way out was found by the famous American inventor Edison, who proposed using an induction coil to amplify the voltage. So the telephone set was supplemented with a transformer. Transformers will be discussed in more detail in a later chapter. Now we will only explain the principle of its work. If you put two coils on the same iron core and pass an alternating current through one of them, then an alternating current is also induced in the second coil. Let's take a closer look at this phenomenon. The changing magnetic field created by the first coil induces a current of a certain voltage in each turn of the second coil. The turns of the coil, as already shown in the previous chapter, can be considered as current sources connected in series. Then the total voltage on the winding of the second coil will be equal to the sum of the voltages of all its turns. If we want to increase the voltage taken from the second coil, we must increase the number of turns. Thus, by changing the number of turns on the second coil, we can get a voltage on it that is less, equal or greater than on the first. However, as the voltage increases, the current decreases by the same factor, so that their product in the first and second coils remains equal (in fact, due to the inevitable losses in the secondary coil, this product is even somewhat less). The transformer effect was discovered simultaneously with the phenomenon of electromagnetic induction, but since only direct current was used in technology for a long time, it did not find application at first. The telephone turned out to be one of the first devices where the transformer (in the form of an induction coil) gained some popularity. In the apparatus created by Edison, the telephone and microphone were included in two separate circuits. The current source, the microphone and the primary winding of the transformer are connected here in one circuit, the other coil and the telephone receiver in another. The principle of operation of this phone is clear: due to the vibration of the membrane, the resistance in the microphone was constantly changing, which is why the direct current of the battery was converted into a pulsating one. This current was applied to the primary winding of the transformer. In the secondary winding, currents of the same shape, but of a higher voltage, were induced. They easily overcame the resistance of wires and could be transmitted over considerable distances. The telephone improved in this way soon became widespread.
At first, the devices communicated with each other in pairs. They did not have switches and calls. To call the subscriber to the device, they simply tapped the membrane with a pencil. Subsequently, Edison introduced electric bells. In 1877, the first central telephone exchange appeared in New Haven (USA). The connection order here was as follows. A subscriber who wanted to talk to a person or institution looked up the required number in the subscriber book and called the central station. When the latter answered, he reported the number he needed, and if this number was not busy, the operator connected him to the required person using special plugs and informed him that the connection was ready. After that, the subscriber turned to the person connected to him. At the end of the conversation, they were separated. Contemporaries very quickly appreciated the convenience provided by the telephone. Soon telephone exchanges were built in all major cities. At the same time, the demand for telephone sets grew. In 1879, Bell created his own telephone company, which soon turned into a powerful concern. Within ten years, more than 100 thousand telephone sets were installed in the USA alone, and after 25 years there were already more than a million. Then this figure increased by an order of magnitude. Bell lived a long life and was able to observe the spread of telephony around the world. He died in 1922, and a kind of moment of silence was honored in his memory: when the coffin with the body of the inventor was lowered into the grave, all telephone conversations stopped. They write that in the United States at that moment more than 13 million phones were silent. Author: Ryzhov K.V.
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