Simrad EQ33-2 Instruction Manual page 31

EQ33-2 Echosounder operation Chapter 5-7
Range start – allows the user to set the displayed depth range to
begin at some point below the surface. For example, a 100 meter dis-
played range can be "phased" downwards, so that the screen shows
a 100 meter section beginning at, say, 200 meters and going to 300
meters depth.
Range – refers to the distance shown from the top to the bottom of
the display screen. Selecting Auto range will cause the EQ33-2 to
change the basic range setting(s) to keep the displayed bottom in
the lower half of the display. For instance, as your boat moves into
deeper waters, the system will automatically switch to a deeper
range, always keeping the displayed bottom in the lower half of the
display. Manual range allows the operator to set the range displayed
on the screen.
Gain – is another way of saying "sensitivity", or possibly "volume".
Increasing the gain setting of the EQ33-2 will allow you to see
smaller and deeper targets. If the gain is set too high, however, you
will begin to see "noise" and unwanted targets. Generally speaking,
you want to set the gain control just below the point that you begin
to see speckles of "noise" between surface and the bottom on the
screen.
White line – is a control which places a white/black line at the
displayed sea floor and blanks out 4 pixels just below the line. The
purpose of this is to help the user detect targets, such as fish, which
are very close to the sea floor and whose echoes tend to merge with
those of the sea floor itself.
Expansion window (zoom level) – can be selected in eight steps,
ranging from 1 to 50 meters, or converted to feet or fathoms (refer to
Setup for units, section 8.3). This function allows you to take a closer
look at a particular section of the water underneath your boat. You
can expand the view near the bottom (Bottom expansion) or near the
Variable Range Marker (VRM expansion).
TVG – Time Varying Gain – is a control that allows the EQ33-2 to
make corrections for most of the losses and absorption that occurs as
sound energy passes through sea water. There are three settings to
choose from, Normal, Special and OFF.
The setting "Normal (20 log R) is for general fish finding at depths
down to 50m (150') and it will also give a uniform bottom echo pres-
entation at shallow, mid and deep water.
The setting "Special (40 log R) will adjust the TVG to show the same