Furuno CH-250 - Manual (Page 75)

4-7
4.9 Range Marker
The range marker functions to measure the range to a target echo (fish school, bottom, etc.)
1. Operate the Omnipad to place the cursor on the location desired.
2. Press the [R/B] key to display the range marker. The range marker appears along with
range indication.
3. To erase the range marker, press the [R/B] key again, or place the cursor on the range
marker and press the [R/B] key.
Range
NAV
DATA
or
A-SCOPE
DISPLAY
Depth, Water Temp. Display
67
Range marker
Figure 4-6 Range marker
4.10 Adjusting the Picture
4.10.1 Displaying weak echoes clearly
Echoes from targets (such as the bottom or a fish) return to the transducer in order of the
distance to them, and when their intensities are compared 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 won’t be able to judge the actual size of the target from the size of echoes displayed on
the screen. To overcome this inconvenience, 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 also functions to suppress unwanted echoes and noise which appears in a certain
range area on the screen.
To adjust TVG:
1. Press the [MENU] key to open the menu.
2. Press to select MENU and then press or to select the ES menu.