Interphase Color Twinscope Operation Manual page 33

the display. In most situations the AUTO gain mode
works well, but manual adjustments will often be
required to get the optimum picture - especially when
looking far ahead in shallow water.
Beam Depth at Various Forward Ranges
Forward Range
250
Beam Depth =
Approx. 0.18 X
Forward Distance
In certain conditions - especially in shallow water -
you may see a horizontal display that shows a target
ahead that remains on the screen at the same
distance - even as the boat moves. This is probably
caused by a transducer sidelobe problem and can be
reduced or eliminated by decreasing the forward
gain.
A sidelobe on the display will show up at a forward
distance equal to the depth - as shown below.
46.2 Ft
Sidelobe at
100
same forward
distance as
depth
Depth
500
45
90
CURSR PWR
VERT HORIZ
DOWN DATA
RANGE GAIN
50
FORWARD LOOKING SONAR
Following a Shoreline or Bank
Bottom getting shallow to Starboard
Following a Channel
33