How Sonar Works - Humminbird 363 Operation Manual

531448-1_A - 363_Man_Eng.qxd 11/9/2005

How Sonar Works

Sonar technology is based on sound waves. The 300 Series
to locate and define structure, bottom contour and composition, as well as depth
directly below the transducer.
Your 300 Series TM Fishing System sends a sound wave signal and determines distance
by measuring the time between the transmission of the sound wave and when the
sound wave is reflected off of an object; it then uses the reflected signal to interpret
location, size, and composition of an object.
Sonar is very fast. A sound wave can travel from the surface to a depth of 240 ft
(70 m) and back again in less than 1/4 of a second. It is unlikely that your boat can
"outrun" this sonar signal.
SONAR is an acronym for SOund and NAvigation
Ranging. Sonar utilizes precision sound pulses or
"pings" which are emitted into the water in a
teardrop-shaped beam.
The sound pulses "echo" back from objects in the
water such as the bottom, fish and other
submerged objects. The returned echoes are
displayed on the LCD screen. Each time a new echo
is received, the old echoes are moved across the
LCD, creating a scrolling effect.
When all the echoes are viewed side by side, an
easy to interpret "graph" of the bottom, fish and
structure appears.
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TM Fishing System uses sonar
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The sound pulses are transmitted at various
frequencies depending on the application. Very
high frequencies (455 kHz) are used for greatest
definition but the operating depth is limited. High
frequencies (200 kHz) are commonly used on
consumer sonar and provide a good balance
between depth performance and resolution. Low
frequencies (83 kHz) are typically used to achieve
greater depth capability.
The power output is the amount of energy generated
by the sonar transmitter. It is commonly measured
using two methods:
• Root Mean Square (RMS) measures power output
over the entire transmit cycle.
• Peak to Peak measures power output at the highest
points.
The benefits of increased power output are the
ability to detect smaller targets at greater distances,
ability to overcome noise, better high speed
performance and enhanced depth capability.
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