Furuno 1830 - Principle of Operation

PRINCIPLE OF OPERATION
The term "RAUAH." is an acronym meaning RAdio Detection And Ranging.
Although the basic principles of radar were developed during World War II,
priinarily by scientists in Great Britain and the United States, the uee of
echoes as an aid to navigation is not a new development.
Before the invention of radar, when running in fog near a rugged shoreline
snips would sound a snort niast on their whistles. fire a shot, or strike a
beil- The tiroe 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 whioh the echo was heard indicated the relative bearing of the
Shore.
Today, the method of determining the distance to a target is mueh more
accurate because of pulse-modulated radar. Pulse-modulated 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 iø a known faet that radar waves travel at a nearly Gonstani 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 eoho 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 in making the range calculation.
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 reneives a returning eoho. Each time the scanner rotates
pulses are transmitted in the full 360® circle. each pulse at a slightly
different bearing from the previous one, Therefore, if we know the
direction in which the signal is sent out we know the direction from which
the echo musi return.
Note that the speed of the radar waves out to the target and back agaln as
rehoes is extramely fast oompared to the speed of rotation of the antenii«.
By the time radar echoes haVe returned to the scanner, the amount of
scanner rotation af ter initial transmission of the radar pulse is extremely
small.
The range and bearing of a target is displayed on what is called a Plan
Position Indicator or PPI. This display is essentially a polar diagram, with
the tran smt ttin g ship^ s position at the centor. Images of target echoes
(sometimes called a "pip”) are received and displayed at their relative
bearings, and at their distance from the PPI center. With a continuous
display of the images of targets, the motion of the transmitting ship is also
displayed.
Target Pip
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