Echo Display
RADAR uses hundreds of pulses per second and receives an indication of each
reflected signal.
The antenna radiates the pulses and shapes the energy into a narrow beam. As the
antenna slowly rotates, an illuminated sweep line from the center of the display to the
outer edge moves around the display (called scanning). This sweep line is synchronized
with the motion of the antenna. If there is no echo (no object in the path of the RADAR
pulse), the sweep line is of uniform intensity on the face of the display. However, if a
RADAR pulse is reflected, it causes the sweep line (or sweep) to momentarily brighten
at the location of the echo. This process is repeated for each pulse sent out or returned.
Echoes from the same object repeatedly brighten the same area, thus making a steady
spot of light. Since the rate at which the pulse travels is known, the sweep can be
marked off to represent the distance the pulse travels in that length of time. These
marks (range marks), assist in determining the echo's (target s) specific distance from
the antenna.
The position of the spot of light (if there is a target echo) on the display shows both the
direction (azimuth) and the distance (range) of the target. The greater the range of a
RADAR set, the slower the antenna rotates. This allows more time for the reflected
return of pulses to travel the greater distance.
NOTE
A term commonly used in the RADAR environment is
―paints.‖ For example, as the RADAR antenna is rotating,
the sweep paints an area on the display.
RADAR Display
There are numerous ways of displaying the RADAR data once it has been obtained.
The manner of presentation depends upon the use intended for the data.
In ATC, the most frequently used type of Digital Audio Surveillance RADAR (DASR)
display is a plan position indicator, commonly referred to as the PPI scope. In this type
of RADAR search indicator, the time reference is at the center of the cathode-ray tube
face. Bearing information is provided through the use of a compass rose. The compass
rose is a circular device. It surrounds the PPI and depicts magnetic bearings from 0 to
350 degrees in 10-degree increments. The DASR has 360 degrees of scan (see Figure
5-16).
5-30
