Navigation and Seamanship (1+1)

6.2.3. Block Diagram of Radar

Components of RADAR

Modulator

Modulator is the heart of the system. It produces electric pulses that triggers the transmitter to send the specified number of radio signals. Also it controls all the time related functions in radar.

Transmitter . The transmitter generates powerful pulses of radio frequency (RF) in the form of short pulses with definite intervals. The radio waves are usually sent in short pulses, with each pulse duration fraction of a microsecond. (A microsecond 1/10,00,000) Enough time interval will be given for the echoes to return back to the antenna. Normally, 50 pulses per second are sent from the transmitter.

Duplexer

The duplexer is an electronic switch that alternately connects the transmitter and receiver to the antenna , which facilitate to transmit the pulse and to receive the echo.

Antenna (Scanner) :

The antenna also known as scanner takes the radio frequency energy from the transmitter and send to air in a well defined directional beam. The antenna system also receives any returning echoes and passes them to the receiver. The antenna is capable of rotating 360^o ( always rotate in clockwise) with a speed of 15-25 rpm .

Receiver

The receiver receives the weak echo signals from antenna, amplifies and produces them as video pulses to be applied to the indicator. The receiver is sensitive to the range of frequencies being transmitted and provides amplification of the returned signal.

Indicator( display unit)

The indicator or display unit produces a visual output to the observer in easily understandable picture of the relative position of radar targets from the scope’s center . Radar determines distance of an object by calculating the time required for a radio signal to travel from a transmitter to an object and return back as echo. The radar can also determine bearing of an object. The common display used in radar is Plan Position Indicator (PPI). The information of return echo is converted into brightness and then displayed in the same relative direction as the antenna orientation.