Installation manual

Basic theory
BASIC THEORY
This chapter explains some of the basic theory related to settings,
error sources and noise conditions.
Topics
Settings on page 171
Noise and reverberation on page 175
Layers and deflections on page 177
Settings
A sonar will transmit a sound wave into the water around the
vessel. When t his sound wave hits fish, bottom, or other objects
in the water, a part of the sound will be returned as echoes.
These echoes are collected by the sonar, interpreted by the sonar
computers, and presented on the display.
The most important interpretation is however left to you, and
it may often be difficult to distinguish the echoes and identify
targets. In order to help you with this, the SH80 sonar provides
numerous advanced filter and gain functions. You can also tilt
the sonar beam vertically in order to achieve an optimum result,
and you can use the vertical slice to view “across” into the water.
This chapter provides you with some basic theory a bout some
of the key settings available.
What is TVG?
TVG means “Time Va ried Gain”. As echoes will be weaker
when the distance to them increase, the sonar will automatically
amplify distant echoes more than close echoes. In practice, the
gain will increase in proportion with how long the sonar must
wait for the echoes.
Figure 29 The TVG principle: The gain at time (B) is larger than at time (A).
A
(CD015005C)
0
1
10 100 1000
C
B
164385/E 171