2. SONAR MODE
2-8
nearly equal. The sonar operator will be quite inconvenienced if these echoes are di-
rectly displayed on the screen, since he won’t be able to judge the actual size of the
target from the size of echoes displayed on the screen. To overcome this inconve-
nience, use the TVG function. It compensates for propagation loss of sound in water:
amplification of echoes on short range is suppressed and gradually increased as
range increases so that similar targets are displayed in similar intensities irrespective
of the ranges to them.
The TVG LEVEL and TIME controls compensate for propagation loss. The effective
distance is up to 1000 m approximately.
The TVG also functions to suppress unwanted echoes and noise which appear in a
certain range area on the screen as shown in the figure above.
1) Set TVG time between 3 and 5. (130 to 300 m approx.) This is the standard setting
and you can maintain it in most cases.
2) When sea surface reflections or plankton layers disturb the picture, set the TVG
level control around 5 to eliminate them.
3) Locate a school of fish on a long range setting which is approaching your vessel.
Adjust the tilt to keep the school of fish in the center of the sonar beam. Check that
the fish echo appears in the same color while it approaches. If the color changes
suddenly to weaker colors as the fish echo nears, the TVG is improperly set. Adjust
the TVG level to correct it. If sea surface reflections and noise remain, try to re-
move them with the interference rejector (“IR” on the SONAR menu) and NL con-
trol as described on section 2-8.
2.7.5
Detecting schools of fish aurally
Occasionally you will be preoccupied with
other tasks and unable to concentrate on
watching the sonar picture. In such cases
it would be a good choice to use the audio
function. This function enables you to
monitor echoes from schools of fish and
bottom through the external speaker (op-
tion), of which the volume can be adjust-
ed with the AUDIO control on the sub
panel 1.
After you become accustomed to utilizing the audio function, you should be able to de-
tect a school of fish from a range longer than you can detect it on the screen. In addi-
tion you may judge whether the schools of fish is approaching or going away; the tone
becomes higher when the fish is approaching and lower when going away.
Noise caused by
strong reflection
of serface
turbulence.
Nearer target
echoes
appear in
larger size.
Reduce gain
for nearby
sreas, using
TVG.
Echoes of same
size target are
presented in same.
Noise is rejected.
Without TVG function
Proper TVG setting
ME NL AUDIO
10 0
10 0
10
ME NL AUDIO
10 0
1
AUDIO
0
10
(Turn clockwise to
get high volume)
SUB PANEL 1
Summary of Contents for CH-37BB
Page 1: ...COLOR SECTOR SCANNING SONAR CH 37BB OPERATOR S MANUAL www furuno com Model ...
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