Thursday, September 7, 2017

Radar Definition and Application

Radar was the name given during World War II to an electronic system by which radio waves were bounced off an aircraft in order to locate its position. The term is an acronym made from the fuller term radio diction and ranging. Development of the earliest practical radar system is usually credited to Sir Robert Watson Watt. The definition is on this link Radar.

A radio transmitter generates radio waves, which are then radiated from an antenna, “illuminating” the airspace with radio waves. A target, such as an aircraft, that enters this space scatters a small potion of this radio energy back to a receiving antenna. This week signal is amplified by an electronic amplifier and displayed on a cathode ray tube (CRT) TV. Thus the presence of the aircraft has been detected, but to determine its position the aircraft distance (range) and bearing must be measured. Because radio waves travel at a known constant velocity-the speed of light, which is 300,000 km/sec. or 186,000 mi/sec-the range may be found by measuring the time talked for a radio wave to travel from transmitter to aircraft and back to the receiver. For example, if the range were 186 miles, the time for the round trip would be (2 x 186) + 186,000 = two thousandths of a second, or 2,000 microseconds. There is no airplane have a speed near to the light speed so the speed of radar will fast enough to detect the airplane position.

The radio frequency pulse is emitted on receipt of a firing signal from a trigger unit that simultaneously initiates the time base sweep on the CRT. Thus the electronic clock is started, and when the echo signal is seen on the tube the time delay can be measured, giving the range, the pulses are emitted at the rate of a few hundred per second so that the operator sees a steady signal.

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