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TextN6(a)

RADAR

The word "radar” means Radio detection and Ranging. Radar equipment is capable of determining by radio echoes the presence of objects, their direction, range and recognizing their character.

There are several types of radar sets, all of them consist of six essential components, namely: a transmitter, a receiver, an antenna system, an indicator(s), a timer, and, of course, a power supply.

A radar set detects objects by sending out short powerful pulses of ultra-high frequency radio wave energy from a highpower transmitter. The directional antenna takes this energy from the transmitter and radiates it in a beam (similar to that of a searchlight).

As the transmitted energy strikes an object, a portion of it is reflected back. The receiver picks up the returning echo through its antenna and translates it into visual readable signals on a fluorescent screen. The appearance of these signals shows the presence of an object within the field of view of radar.

The electron beam sweeps across the fluorescent screen in somewhat the same way as a hand sweeps across the face ofclock. Just as the hand of a clock complete its sweep in sixty seconds, the electron beam can be made to travel across any desired portion of the screen in some predetermined interval of time. It is the timer, which is the synchronizer of the whole system that times the transmitter pulse and the indicator. The use of these timed pulses and the fact that the radio waves travel at the constant velocity of light gives a simple means of measuring range. The accuracy with which time is measured determines the accuracy of the range.

How then is the direction in which an object lies to be found? Both azimuth and elevation can be determined by means of the directional antenna. The antenna may be rotated as the pulses are sent out and the strongest signal appears on the screen.

During the last few decades, a subtle change has occurred which none of our senses can register. Radio waves, bearing messages in many tongues, flow ceaselessly around us, through us and above us. We can only hear and see them if we convert them to other waves to which our ears and eyes are receptive.

Radio waves are the longest members of the family of electromagnetic waves. In the spectrum, in which the waves are arranged in order of increasing wavelength, they lie beyond the infrared waves. Their wavelengths range from about three hundredths of centimetre to about 300 kilometers. Radio broadcasts today are made by two different methods known as AM (amplitude modulation) and FM (frequency modulation). The frequencies of the waves used are expressed in kilocycles or megacycles. The vibrating current is fed into an antenna from which the radio waves are broadcast into space.

Microwaves are the smallest radio waves. In the spectrum of electromagnetic waves they lie between infrared rays and the long radio waves. The shortest microwaves have a wavelength of about three hundredths of a centimetre and a frequency of one million megacycles. The longest microwaves have a wavelength of about 'three metres and a frequency of one hundred megacycles.

The first microwaves made by man were the two-foot waves produced by Heinrich Heitz. It is interesting that they were the last to be put to a practical use. Long waves were easier to produce and send out over long distances. Scientists had to return to the use of short waves in order to solve a problem that came up during World War II. The problem was "How can you detect an approaching enemy plane while it is still far away?" A possible answer to the problem was to send a beam of radio waves. Long radio waves could not be used for this purpose because they fan out too quickly from the broadcasting antenna. Very short waves were necessary to make the radar system work. So new transmitters and receivers were designed to make and use microwaves.

Find answers to the following questions:

1. Can we hear and see radio waves? 2. What place do radio waves occupy in the spectrum of electromagnetic waves⁹ 3. Who produced the first microwaves? 4. Were the microwaves the first to be put to a practical use⁰ 5. What kind of problem came up during World War 11?

Speak about the characteristics of radio waves and