Onwa Marine Electronics KR-12X8 - Manual (Page 14)

1. PRINCIPLE OF OPERATION
The term "RADAR" is an acronym meaning "RAdio Detection And Ranging".
Although the basic principles of radar were developed during World War II,
Before the invention of radar, when running in fog near a rugged shoreline,
ships would sound a short blast on their whistles, fire a shot, or strike a bell.
The time between the origination of the sound and the returning of the echo
indicated how far the ship was from the cliffs or the shore. The direction from
The bearing to a target found by the radar is determined by the direction in
which the radar scanner antenna is pointing when it emits an electronic pulse
and then eceives a returning echo. Each time the scanner rotates pulses are
transmitted in the full 360 degree circle, each pulse at a slightly differentbearing
from the previous one. Therefore, if one knows the direction in whichthe signal
Note that the speed of the radar waves out to the target and back again as echoes
is extremely fast compared to the speed of totation of the antenna. By the time
radar echoes have returned to the scanner, the amount of scanner rotation after
Radar determines the distance to the target by calculating the time difference
between the transmission of a radar signal and the reception of the reflected
echo. It is a known fact that radar waves travel at a nearly constant speed of
162,000 nautical miles per second. Therefore the time required for a transmitted
signal to travel to the target and return as an echo to the source is a measure
of the distance to the target. Note that the echo makes a complete round trip,
but only half the time of travel is needed to determine the one-way distance to
the target. This radar automatically takes this into account it making the range
echoes as an aid to navigation is not a new development.
which the echo was heard indicated the relative bearing of the shore.
is sent out, one knows the direction from which the echo must return.
initial transmitting of the radar pulse is extremely small.
calculation.
1.1 What is Radar?
1.2 How Ships Determined Position Before Radar
1.4 How Radar Determines Bearing
1.5 Radar Wave Speed and Antenna Rotation Speed
1.3 How Radar Determines Range
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