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Radar


Radar
One of the most important areas of application become radio radar, that is, the use of radio waves to locate invisible targets (as well as the speed of its movement). The physical basis for radar is the ability of radio waves reflect (scatter) from the object, the electrical properties are different from the electrical properties of the environment.

Even in 1886, Heinrich Hertz discovered that radio waves can be reflected by metal and dielectric bodies, and in 1897, working with its radio transmitter, Popov discovered that radio waves are reflected from the metal parts of ships and their body, but neither one nor the other did not study in depth this phenomenon.

The idea occurred to radar German inventor Hyulsmayeru, who in 1905 received a patent for a device in which a radio wave reflection effect has been used to detect ships. Hyulsmayer suggested to use a radio transmitter, the rotating directional antennas, radio with light or sound indicator, perceiving objects reflected waves. For all its imperfection device Hyulsmayera contain all the essential elements of modern radar. The patent, issued in 1906, Hyulsmayer described a method of determining the distance to the reflecting object. However, the development of practical applications Hyulsmayera not received. It took thirty years before the idea to use radio waves to detect aircraft and ships could be translated into a real instrument. Implement it used to be impossible for the following reasons. As Hertz, Popov and used for his experiments with short waves. In practice, the radios up to 30-ies of the XX century, applied the very long waves. Meanwhile better reflection occurs, provided that the wavelength at least equal to, or (more preferably) less than the size of the reflecting object (airplane or ship). Consequently, the long waves that were used in the radio, could not give a good reflection. Only in the 20s US radio amateurs, who were allowed to use for his experiments on the radio short waves have shown that in fact these waves for unknown reasons, while subject to extremely long distances. With negligible power radio transmitters to radio amateurs able to implement communication across the Atlantic Ocean. This attracted the attention of short waves, scientists and professionals.

In 1922, employees of the Naval Research Laboratory radiootdela Taylor and Young, working in the range of VHF, radar observed phenomenon. They immediately got the idea that it is possible to develop such a device in which destroyers are located from each other at a distance of several miles, will be able to immediately detect the enemy ship, "regardless of the fog, darkness and smoke screen." His report on the Taylor and Jung sent to the US Department of the sea, but to support their proposal did not receive. In 1930, one of Taylor's scientific staff engineer Hyland, conducting experiments on radio on shortwave, said that when the aircraft crossed the line on which are located the transmitter and receiver, appeared distorted. Hyland concluded from this that with the transmitter and receiver operating at short wavelengths, it is possible to detect the location of the aircraft. In 1933, Taylor, Jung and Hyland took a patent for his idea.

At this time the radar was to be born - it developed all the technical prerequisites. The main thing was that it became necessary war. air defense technology between the two world wars has not been a corresponding development. As before, the main role was played by positions aerial surveillance, warning and communication, balloons, searchlights, zvukouloviteli. Due to the growth rate bombers notification posts had to be put forward for 150 kilometers or more from the city, for the protection of which they were intended, and laid him in a long telephone lines. However, these positions still did not give full security guarantees. Even in good clear weather observers could not detect planes flying at low altitude. At night or in fog in cloudy weather such positions did not see the aircraft and were limited reports of "noise of engines." I had to have these positions in several zones, throw them in a staggered manner to cover them all distant approaches.

Similarly, the spotlights were reliable only on clear nights in the fight against the aircraft. When low clouds and fog, they became useless. Specially designed zvukouloviteli were also weak detection means. Let us imagine that the airplane is 10 km from the observation post. engine sound became audible listener zvukoulovitelya 30 seconds with a minor. During this time the aircraft flying at a speed of 600 km / h, time to fly 5 km, and zvukoulovitel therefore pointed out the place where the plane was half a minute ago. Under these conditions, use zvukoulovitelem to put things with the help of a spotlight or anti-aircraft gun, it was pointless. That is why in all the countries of Europe and in the US for 6-7 years before World War II began intensive search of new means of air defense that can prevent an attack from the air. In the end, the most important role was assigned to radar. As is known, fog, clouds, darkness does not affect the propagation of radio waves. The spotlight fades quickly in the thick clouds, and for radio waves such obstacles do not exist. It made a very promising idea to apply them for the needs of defense.

However, the practical implementation of the idea of ​​radar solutions require a number of complex scientific and technical problems. In particular, it was necessary to create generator VHF and sensitive detectors of very weak signals reflected from objects. Only in 1938, the US Naval Research Laboratory developed a signal from the radar XAF steps 8 km range, which has been tested on the battleship "New York." By 1941, 19 of these radars were manufactured.

It is much more productive to go work in the UK, where the government did not stint on the costs. Already in 1935 under the leadership of Watson-Watt's first impulse radar early warning CH it was created. She has worked in the 10-13 m wavelength range and had a range of 140 km at an aircraft altitude 4, 5 km. In 1937, already 20 of these stations were established on the east coast of England. In 1938, they started to clock duty that lasted until the end of the war.

Although the device of any radar very difficult, its operating principle is easy to understand. Radar does not work continuously, and periodic jolts - pulses. The transmitter first English CH radar station sends a pulse 25 times a second. (Sending pulse lasts modern locators few millionths of a second, and the pause between the pulses -. A few hundredths or thousandths of a second) pulse mode is used to measure the time between sending the pulse and the return reflection from the object. Having sent into space is very short-term "portion" of radio waves, the transmitter automatically turns off and begins to work the radio. Having met on the way to spread an obstacle, radio waves are scattered in all directions and partially reflected from it back to the place of sending waves, ie the radar. This process is similar to the reflection of sound waves - a phenomenon echo. Suffice to shout or hit his hands in a valley at the foot of the cliffs - and a few seconds later hear a faint echo - reflection of sound. Since the speed of radio waves almost a million times greater than the speed of sound waves from the rock at a distance of 3500 meters, the echo returns after 20 seconds, and a radio wave - two-thousandth of a second. Therefore, the main feature of the radar should be rapid measurement of the shortest periods of time up to a millionth of a second. It is clear that if the radar continuously sends its signals, among the powerful transmitter signal would not be possible to capture very weak reflected radio waves returned back. The antenna of the radar has directed action. Unlike antennas broadcasting station sends radio waves in all directions, the pulses emitted by the radar, are concentrated in a very narrow beam that is sent in a very specific direction.

Having reflected pulses, radar guided them on a cathode ray tube. Here, the momentum (of course, many times reinforced) was applied to the vertical plates, controlled by an electronic ray tube (see. Its unit in the previous chapter) and caused a vertical beam throw on the radar screen. As can be seen on this screen? 25 times per second in the left part arose electronic pulse (this cast was due to the fact that a very small part of the energy of the emitted pulse fell to the receiver), and it ran right scan line. It lasted as long as the momentum is not reached the goal, it does not reflect on it and did not return back. Assume that the line drawn by the electron beam moving across the screen within 1 millisecond. During this time the pulse passes 150 km to the goal, reflected from it, came back to the station and displayed on the screen in the form of a second roll. At the point of the tube screen, where there was the first throw, put 0, and at the end of the line - 150 km. Since the wave propagation velocity is constant, the whole line can be divided into equal parts and thus obtain the ability to read (within 150 km of) any distance to the target, the reflected pulse which was visible on the handset screen. With such frequent appearance of the image on the screen, it seemed as if the eye of the operator fixed and non-vanishing. Only the pulse reflected from the target, slowly moved to the left on the line, if the plane was flying toward the station.

All the information on the detected aircraft radar of the enemy passed the so-called "center of the filter." Here, according to the reports of the individual stations was carried out comparisons and update the data on air situation. Selected and proven information "center filter" transferred command. The central command post there was a large map. Special operators move around the map a little model airplanes. Command therefore would continuously monitor the traffic situation and according to this to take the necessary decisions. Later it turned out that the early warning station and may give additional information about the number of enemy aircraft, their course and speed. Team defense items to these reports could infer how many bombers involved in the operation, to establish to what point they are sent to and when it will arrive.

However, the first radar and had major shortcomings. As they worked on a wave of 10 meters or more, their antennas are bulky and immobile. For example, CH transmitter antenna was suspended on masts in height to 120 m. Nearby is the receiving station with an antenna at a height of 80 m. With a directional effect, these antennas emit radio waves wide cone forward and somewhat away from the main direction. Left, right and back, these antennas do not radiate, and therefore these directions radars can not detect aircraft. Because of their wave reflected from the ground and water, low-flying targets were not accessible to them. So planes approaching to England at an altitude of less than 100 m, could fly silently to radar.

Eliminate these flaws could only be the creation of new radar stations operating at shorter wavelengths. In the early days of radar waves were applied to 10-15 m in length, but later it turned out that it is more convenient to use for this purpose the waves a thousand times shorter - of the order of a few centimeters. Devices operating in this band prior to the beginning of the war were, in fact, the laboratory designs were very moody and had a negligible power. Known at the time types of vacuum tubes is very bad or hardly working at centimeter wavelengths. All necessary equipment for more advanced radar was set up in record time at the beginning of the war.

First we went to the wave 1, 5 m, which allowed the right to improve radar performance and dramatically reduce the size of the antennas. Then came the idea that such an antenna can be rotated in the horizontal direction and to send impulses locator in all directions, not only forward. Further it suggested itself suggested that if the radar alternately sends pulses and receives their reflection, it is not necessarily transmitting and receiving stations placed separately: can and should transmit and receive on the same antenna alternately connecting it then to the transmitter, then the receiver. In 1939 CHL station was designed to detect low-flying aircraft and surface ships with a range of 100 km range. These stations were located at a distance of 40 km from each other, protecting the mouth of the Thames and the approaches to it. In the future, the number of stations was increased so as to cover the entire east coast of England. The introduction of a number of improvements which increased the range of the radar to 160-190 km.

All these measures are more than paid off in 1939-1940, when unfolded grand Battle of Britain. Not being able to redeploy its troops to England, Hitler moved against her armada of their bombers. English fighters did not know no rest day nor night, fighting off one after another air attack the Germans. Radar early warning stations played a huge role this time in the entire air defense system. German pilots soon became convinced that the invisible radar beams for their terrible fighters and anti-aircraft guns. The use of radar has guided the British soon the idea to target with its radar fighter bombers to the enemy. For this small radars were created (GCI). They had a range of smaller, but more accurately determined the position of enemy aircraft. These radars are installed far away from the airfield fighter aircraft. After receiving a message from the early warning stations, they began to keep track of the approaching enemy, giving the fighter pilots accurate data on the location of the enemy.

For the former station of this type cathode ray tube with a horizontal scanning line has been inconvenient, since every time she could watch only one plane and constantly had to switch from one target to another. In this regard, there was a major improvement in radar technology - now the so-called tube-round view, received in a short time the most widely used in many types of plants. On the screen, a tube light scanning line does not begin with the left edge of the screen, as in previous designs, and from the center. This line is rotated clockwise simultaneously with the rotation of the antenna, reflected on the screen the location of purposes around the station. Such a screen is created as if the air situation map. Light spot in the center of the screen marks the location of the radar station. Concentric rings around this spot helped determine the distance to the reflected pulses, which were designated as a bright dot. The officer pointing stations simultaneously watched on this screen for all those interested in its aims. Implementation guidance is greatly simplified. It is clear that this way of working the radar display was not fit above, since all the signals reflected from objects instantly disappeared from the screen. There used screens that have so-called "afterglow" that is, preserving the light for a certain period of time. In such tubes the electron beam deflection was carried out using a coil in which current is varied linearly with time.

The use of radar defense systems in the first period of the war had produced tangible results. For four months of 1940 in the skies over England it was destroyed more than 3,000 German aircraft, and 2,600 of them were shot down by fighters, induced by their radars. Due to the large losses the Germans were forced to stop the daily attacks. However, this did not save them. Britons urgently small radar AI, located on board the aircraft was developed. She could detect targets at a distance of 3-5 km. The new radars are equipped with special night fighters. In addition to the pilot on their radio operator-gunner was located. On a tip-off from the ground such aircraft approaching German bombers in the range of vision of his radar. After that, the operator itself, with the face of the handset locator, giving the pilot team for internal intercom where to send the car to get close to the bombers. By the spring of 1941, the system of night radar defense has justified his appointment. In January the British shot down a total of 4 German night bombers, the 58 April, and in May 102.

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