How Sonar Works - Humminbird 383c Operation Manual

531450-1_A - 383c_Eng.qxd 11/18/2005

How Sonar Works

Sonar technology is based on sound waves. The 300 Series™ Fishing System uses sonar
to locate and define structure, bottom contour and composition, as well as depth
directly below the transducer.
Your 300 Series™ 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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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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