How Sonar Works - Humminbird 777C2 Operation Manual

531474-1_A_777c2_English.qxd 11/3/2005

How Sonar Works

Sonar technology is based on sound waves. The 700 Series™ Fishing System uses
sonar to locate and define structure, bottom contour and composition, as well as
depth directly below the transducer.
Your 700 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.
8:01 PM Page 6
1
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.
2