Furuno CSH-53 Fine Tuning The Picture, Eliminating Unwanted Feeble Echoes, 1 Principle of TVG

FINE TUNING THE PICTURE

Eliminating Unwanted Feeble Echoes

Echoes from targets such as seabed and fish return to the trans- ducer in order of distance to them, and when we compare their intensities at the transducer face, those from nearer targets are generally stronger when their reflecting properties are nearly equal. The sonar operator will be quite inconvenienced if these echoes are directly displayed on the screen, since he can not judge the actual size of the target from the size of echoes dis- played on the screen. To overcome this inconvenience, the TVG function is incorporated. It compensates for propagation loss of sound in water; amplification of echoes on short range is sup- pressed and gradually increased as range increases so that simi- lar targets are displayed in the similar intensities irrespective of the ranges to them.

The CSH-53 has three TVG functions, NEAR, MEDIUM and FAR, and they mainly compensate for propagation loss on short, middle and long ranges respectively, centered at the ranges shown below. The higher the TVG setting the greater the amplification of echoes.

Near
About	100	m	Med
			About
				400	m

Figure 3-1 Principle of TVG

Far

The TVG is also used to suppress unwanted echoes and noise which appear in a certain range area on the screen such as sea surface reflections and cruising noise. To set TVG properly, do the following:

How to adjust TVG

1.Open sub panel 2.

2.Select TVG•TX.

3.Set TVG NEAR, MEDIUM and FAR to 5.

3-1