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Radar -  facts about earth and technology

Radar stands for Radio Direction And Range. It was first developed in the late 1930s after scientists had noticed that aircraft reflected the radio signals transmitted from broadcasting stations. Today, in a highly sophisticated form it is used to navigate ships in fog, land aircraft in low visibility, detect and control missiles and catch motorists who are exceeding the speed limit. Radar works by transmitting a very high power pulse of radio energy for a short period.

Radar - kids facts about earth

Radar - kids facts about earth

When the radar signal is a narrow beam of waves, the reflected 'echo' is a bump in the line of an oscilloscope trace (click image to increase)

When the beam is spread out over a wider area, the ships show up as bright patches around the oscilloscope screen

The radio energy spreads out from the radar set at a speed of about 186,000 miles per second. Any object in its path such as a ship or an aircraft will reflect some of the energy back towards the radar set - like a mirror reflecting light. In the radar set a radio receiver picks up the reflected energy and electronic circuits measure how long it took for the energy to travel to the object and back. If the time taken was one second then the energy must have traveled 186,000 miles and the object must be half as for as this (93,000 miles) away. For an object only 164 yards away the time interval is only one microsecond; but this can be measured very easily with modern electronic circuits.

The direction in which a target lies is determined by arranging to send the radar pulse out in one direction only using a directional antenna. The antenna can be rotated automatically or by hand until reflected energy, an echo, is picked up. The object clearly lies in the direction in which the antenna is pointing.

Navigational radar sets on ships normally use a type of display known as a Plan Position Indicator, or P.P.I. The radar antenna is rotated continuously at about 20 revolutions per minute. At the same time a radial line on a cathode ray tube on the bridge of the ship rotates to 'point' the display.

When an echo is received a spot of light appears on the line. The center of the tube is the ship's position: the distance on the tube between the center and the echo tells the captain how far the ship producing it is away from him. He can tell the direction of the ship from the direction of the echo from the center of the tube. At this page you can find more kids facts about earth.

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