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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Radar. History of invention and production
Directory / The history of technology, technology, objects around us Radar station (radar), radar (English radar from radio detection and ranging - radio detection and ranging) - a system for detecting air, sea and ground objects, as well as for determining their range, speed and geometric parameters. It uses a method based on the emission of radio waves and the registration of their reflections from objects.
One of the most important applications of radio has become radar, that is, the use of radio waves to determine the location of an invisible target (as well as the speed of its movement). The physical basis of radar is the ability of radio waves to reflect (scatter) from objects whose electrical properties differ from the electrical properties of the environment. Back in 1886, Heinrich Hertz discovered that radio waves can be reflected by metal and dielectric bodies, and in 1897, working with his radio transmitter, Popov discovered that radio waves are reflected from the metal parts of ships and their hulls, but neither of them began to study deeply this phenomenon. The idea of radar was first conceived by the German inventor Hülsmeier, who in 1905 received a patent for a device in which the effect of reflecting radio waves was used to detect ships. Hulsmeier suggested using a radio transmitter, rotating directional antennas, a radio receiver with a light or sound indicator that perceives waves reflected by objects. For all its imperfection, Hülsmeier's device contained all the basic elements of a modern locator. In a patent issued in 1906, Hülsmeier described a method for determining the distance to a reflective object. However, Hülsmeier's developments have not received practical application. It took thirty years before the idea of using radio waves to detect aircraft and ships could be translated into real equipment. This was previously impossible for the following reasons. Both Hertz and Popov used short waves for their experiments. In practice, radio engineering up to the 30s of the XX century used very long waves. Meanwhile, the best reflection occurs under the condition that the wavelength is at least equal to or (even better) less than the dimensions of the reflecting object (ship or aircraft). Consequently, the long waves used in radio communication could not give a good reflection. It was only in the 20s that US radio amateurs, who were allowed to use short waves for their experiments in radio communication, showed that in fact these waves, for reasons unknown at that time, propagate over unusually long distances. With the negligible power of radio transmitters, radio amateurs managed to communicate across the Atlantic Ocean. This attracted the attention of scientists and professionals to short waves. The first German active radar experiment was carried out in March 1935. During this experiment, many transmitters and receivers were able to detect a weak signal bouncing off a German warship one mile away. Similar developments were also carried out in France, Italy, the USSR and, on a somewhat smaller scale, in Japan. The system, demonstrated at Pelzenhaken on September 26, was the direct result of research led by the brilliant German physicist Rudolf Kuhnold. In the mid-30s, Kunold owned a small corporation called "Gesellschaft fur Elektroakustische und Mechanische Apparate" (GEMA), which specialized in the development of complex radio transmitters and receivers. GEMA had close ties with the German Naval Research Institute. From the middle of 1935, GEMA, although not officially associated with the German military-industrial complex, began to take an active part in the preparations for war.
In 1922, employees of the radio department of the Marine Research Laboratory Taylor and Jung, working in the ultrashort wave range, observed the phenomenon of radar. They immediately came up with the idea that it is possible to develop such a device in which destroyers, located at a distance of several miles from each other, can immediately detect an enemy ship "regardless of fog, darkness and smoke." Taylor and Jung sent their report on this to the US Department of the Navy, but their proposal did not receive support. In 1930, one of Taylor's researchers, engineer Hyland, while conducting experiments on short-wave radio communications, noticed that distortions appeared when the aircraft crossed the line on which the transmitter and receiver were located. From this Hyland concluded that with the help of a radio transmitter and receiver operating on short waves, the location of the aircraft could be located. In 1933, Taylor, Jung, and Hyland took out a patent for their idea. This time the radar was destined to be born - for this there were all the technical prerequisites. The main thing was that it became necessary for the military. Air defense technology between the two world wars did not receive a corresponding development. As before, the main role was played by air observation posts, warning and communications, balloons, searchlights, and sound pickups. Due to the increase in the speed of the bombers, warning posts had to be put forward 150 or more kilometers from the city they were intended to protect, and long telephone lines had to be laid to them. However, these posts still did not give a complete guarantee of security. Even in good clear weather, observers could not detect aircraft flying at low altitude. At night or in fog, in cloudy weather, such posts did not see aircraft at all and were limited to reports of "engine noise". We had to arrange these posts in several belts, scatter them in a checkerboard pattern in order to cover all the distant approaches with them.
In the same way, searchlights were only reliable against aircraft on clear nights. With low clouds and fog, they became useless. Specially designed sound detectors were also a poor means of detection. Imagine that the plane is 10 km away from the observation post. The sound of the motor became audible to the ear of the sound pickup after 30 seconds. During this time, an aircraft flying at a speed of 600 km / h managed to fly 5 km, and the sound pickup, therefore, indicated the place where the aircraft was half a minute ago. Under these conditions, it was pointless to use a sound pickup to direct a searchlight or anti-aircraft gun with it. That is why in all European countries and in the USA, 6-7 years before the Second World War, an intensified search began for new air defense systems that could warn of an air attack. In the end, the most important role here was assigned to radar. As you know, fog, clouds, darkness do not affect the propagation of radio waves. A searchlight beam quickly dims in thick clouds, and there are no such obstacles for radio waves. This made the idea of using them for air defense needs very promising. However, the practical implementation of the idea of radar required the solution of a number of complex scientific and technical problems. In particular, it was necessary to create generators of ultrashort waves and sensitive receivers of very weak signals reflected from objects. It was not until 1938 that the US Naval Research Laboratory developed the XAF signaling radar with a range of 8 km, which was tested on the battleship New York. By 1941, 19 such radars had been manufactured. Work was much more productive in England, whose government did not skimp on spending. Already in 1935, under the leadership of Watson-Watt, the first pulsed early warning radar CH was created. It operated in the wave range of 10-13 m and had a range of 140 km at an aircraft flight altitude of 4 km. In 5, 1937 such stations were already installed on the east coast of England. In 20, they all began round-the-clock duty, which continued until the end of the war. Although the device of any radar is very complicated, the principle of its operation is not difficult to understand. The radar station does not operate continuously, but with periodic shocks - impulses. The transmitter of the first English CH radar station sent pulses 25 times per second. (Sending a pulse lasts a few millionths of a second in modern locators, and pauses between pulses are several hundredths or thousandths of a second.) The pulse mode is used to measure the time between sending a pulse and returning it from a reflected object. Having sent a very short "portion" of radio waves into space, the transmitter automatically turns off and the radio receiver starts working. Having encountered some obstacle on the way of its propagation, radio waves are scattered in all directions and partially reflected back from it, to the place where the waves were sent, that is, to the radar station. This process is similar to the reflection of sound waves - the echo phenomenon. It is enough to shout or clap your hands in a mountain gorge at the foot of a cliff - and in a few seconds a faint echo will be heard - a reflection of the sound. Since the speed of radio waves is almost a million times greater than the speed of sound waves, then from a rock located at a distance of 3500 m, the echo will return in 20 seconds, and the radio wave - in two hundred-thousandths of a second. Therefore, the main feature of the radar station should be the rapid measurement of the shortest periods of time with an accuracy of millionths of a second. It is clear that if the radar station continuously sent its signals, then among the powerful signals of the transmitter it would be impossible to catch very weak reflected radio waves that returned back. The radar antenna is directional. Unlike the antennas of a broadcasting station, which send out radio waves in all directions, the pulses emitted by the radar are concentrated into a very narrow beam sent in a strictly defined direction. Having received the reflected pulses, the radar directed them to the cathode ray tube. Here, this pulse (obviously amplified many times over) was applied to the vertical plates that controlled the electron beam of the tube (see its device in the previous chapter) and caused a vertical throw of the beam on the radar screen. What could be seen on this screen? 25 times per second, an electronic pulse appeared on its left side (this surge was caused by the fact that a very small part of the energy of the emitted pulse hit the receiver), and a scanning line ran after it to the right. This continued until the impulse reached the target, was not reflected from it and did not return back.
Assume that a line drawn by an electron beam moves across the screen for 1 millisecond. During this time, the impulse traveled 150 km to the target, reflected from it, returned back to the station and was displayed on the screen in the form of a second throw. At the place of the tube screen where the first throw appeared, they set 0, and at the end of the line - 150 km. Since the speed of wave propagation is constant, this entire line could be divided into equal parts and in this way it would be possible to read (within 150 km) any distance to the target, the reflected pulse of which was visible on the screen of the tube. Due to such a frequent appearance of the image on the screen, it seemed to the operator's eye as if motionless and non-disappearing. Only the impulse reflected from the target moved slowly to the left along the line if the plane was flying towards the station.
All information about the detected enemy aircraft was transmitted by radar stations to the so-called "filtering center". Here, according to the reports of individual stations, a comparison and refinement of data on the air situation was carried out. The "filtering center" handed over the selected and verified information to the command. There was a large map at the central command post. Special operators moved small models of aircraft around the map. Thus, the command could continuously monitor the air situation and, accordingly, make the necessary decisions. Subsequently, it turned out that early warning stations could also provide additional information about the number of enemy aircraft, their course and speed. Based on this information, the air defense command posts could conclude how many bombers were participating in the operation, determine to which point they were heading and when they would arrive. However, the first radars also had major drawbacks. Since they worked on a wave of 10 meters or more, their antennas were bulky and motionless. For example, the CH transmitter antenna was suspended from masts 120 m high. Nearby was a receiving station with an antenna at a height of 80 m. Having a directional effect, these antennas radiated radio waves in a wide cone forward and somewhat away from the main direction. To the right, to the left and back, these antennas did not radiate, and, consequently, the radars could not detect aircraft in these directions. Since their waves were reflected from the ground and water, low-flying targets were inaccessible to them. So aircraft approaching England at an altitude of less than 100 m could fly unnoticed by radar. These shortcomings could be eliminated only by the creation of new radar stations operating on shorter wavelengths. In the early years of the development of radar, waves 10-15 m long were used, but later it turned out that it was more convenient to use waves a thousand times shorter for this purpose - on the order of several centimeters. Devices operating in this range, before the start of the war, were essentially laboratory designs, were very capricious and had negligible power. The types of vacuum tubes known at that time worked very poorly or almost did not work at centimeter wavelengths. All the necessary equipment for more advanced radars was created in record time at the beginning of the war. First, they switched to a wave of 1 m, which made it possible to immediately improve the performance of the radar and drastically reduce the size of the antennas. Then the idea arose that such an antenna can be rotated in a horizontal direction and send radar pulses in all directions, and not just forward. Further, it was suggested that if the radar alternately sends pulses and receives their reflections, then it is not at all necessary to place the transmitting and receiving stations separately: it is possible and should transmit and receive on the same antenna, alternately connecting it to the transmitter, then to the receiver. In 5, the CHL station was developed to detect low-flying aircraft and surface ships with a range of 1939 km. Such stations were located at a distance of 100 km from each other, protecting the mouth of the Thames and approaches to it. Subsequently, the number of stations was increased so as to cover the entire east coast of England. The introduction of a number of improvements made it possible to increase the range of the radars up to 40-160 km. All these measures more than justified themselves in 1939-1940, when the grandiose battle for England unfolded. Unable to transfer his troops to England, Hitler sent his armada of his bombers against her. English fighters did not know peace day or night, repulsing one after another German air attacks. At that time, early warning radar stations played a huge role in the entire air defense system. German pilots soon became convinced that invisible radar beams were more terrible for them than fighters and anti-aircraft guns. The use of radar soon led the British to the idea of aiming their fighters at enemy bombers with the help of radar. To do this, small radar stations (GCI) were created. They had a shorter range, but more accurately determined the position of enemy aircraft. These radars were installed near fighter airfields. After receiving a message from early warning stations, they began to monitor the approaching enemy, giving fighter pilots accurate data on the location of the enemy. For stations of this type, the old cathode ray tube with a horizontal scanning line was inconvenient, since it could only observe one aircraft at a time and had to constantly switch from one target to another. In connection with this, a major improvement in radar technology took place - the so-called all-round viewing tube appeared, which soon became widespread in many types of stations. On the screen of such a tube, the light scanning line did not start from the left edge of the screen, as in previous designs, but from the center. This line rotated clockwise at the same time as the antenna rotated, reflecting on the screen the location of targets around the station. Such a screen created, as it were, a map of the air situation. A spot of light in the center of the screen marked the location of the radar station. The concentric rings around this spot helped determine the distance to the reflected pulses, which appeared as brighter dots. The guidance station officer simultaneously watched on such a screen for all the targets of interest to him. The implementation of guidance has been greatly simplified. It is clear that on such a radar the method of operation of the indicator described above was not suitable, since all signals reflected from objects instantly disappeared from the screen. Here, screens were used that had the so-called "afterglow", that is, they retained the glow for a certain period of time. In such tubes, the electron beam was deflected using coils in which the current varied linearly with time. The use of all radar defense systems already in the first period of the war gave tangible results. In four months of 1940, more than 3000 German aircraft were destroyed in the skies over England, and 2600 of them were shot down by fighters guided by their radar stations. Due to heavy losses, the Germans were forced to stop daytime raids. However, this did not save them. The British urgently developed a small AI radar station, located on board the aircraft. She could detect targets at a distance of 3-5 km. Special night fighters were equipped with new radars. In addition to the pilot, they housed a gunner-radio operator. On a tip from the ground, such aircraft approached the German bombers within the visibility range of their radar. After that, the operator himself, having the locator tube in front of his face, gave the pilot commands on the internal intercom, where to direct the car in order to get close to the bombers. By the spring of 1941, the night radar defense system was already justifying its purpose. If in January the British shot down only 4 German night bombers, then in April 58, and in May 102. Author: Ryzhov K.V.
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