Basic theory
BASIC THEORY
This chapter explains some of the basic theory related to settings, error sources and noise conditions.
Settings
A sonar will transmit a sound wave into the water around the vessel. When this 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 SH40 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 sonar’s vertical slice to view “across” into the water.
This chapter provides you with some basic theory about some of the key settings available.
TVG
TVG means “Time Varied 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.
(CD015005C)
302656/A
0
A
C B
1 10 100 1000
The drawing illustrates the TVG principle: The gain at time (B) is larger than at time (A).
When you choose the TVG setting you can either switch it off, or choose a “X log R” value. The different settings determine how much gain the sonar will use as time elapses along the X-axis. A higher value for “X” will make the angle (C) steeper.
Default setting on the SH40 sonar is 20 log R .
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