CVS-841/851
Chapter 8
Trouble Shooting
8.4 Setting the video threshold
The bottom detection capability of the sounder may be affected by the transmitting power level,
frequency, transducer type, and its mounting location in the hull. If you encounter unstable digital
bottom depth indication on the display, please use the following procedure to obtain a correct and
stable bottom depth indication.
NOTE:
The following settings should be done in your ordinary fishing ground.
Setting procedure for the bottom detection threshold
(1) Activate the A-Scope display by the following order; Menu -> Display -> A Scope -> ON.
(2) Select the frequency by setting the image mode switch to NORM(H) or NORM(L).
(3)
Select the Depth Measurement sub menu by; Menu -> System -> Depth Measurement -> High
Frequency or Low Frequency.
NOTE:
When this sub menu is selected, the sonar image sensitivity may be reduced. You do not
worry about this, because it is the processed video for the bottom detection.
(4) To determine the best setting, use the following procedure.
a. Observe the A Scope in which a threshold graph is shown. The threshold level is being preset
to –40 for both HIGH and LOW frequencies. Adjustable range is from –80 to 40.
b. Use the up and down key to allow the graph to touch the right end of the green bottom video.
Read the threshold value at this time.
c. Again, press the down arrow key to reduce the value by 6. This setting is considered to be an
optimum level that covers most likely case in the bottom detection. Adjust this value somewhat
plus or minus according to the case, if required.
d. Too much reduced setting may cause a faulty bottom depth indication as a result of detecting
schools of fish in a shallow depth as a bottom. Too much setting, on the other hand, causes no
bottom depth indication with the XXXX display shown in the digital depth window.
e. The above setting can also be made without showing the A Scope. When the XXXX display is
shown, simply reduce the threshold until the bottom depth value is stably shown. Then, further
reduce the threshold value by 6. This sets an optimized detection threshold.
f. Press the MENU key to fix the setting. Repeat the same procedure from step 2 for other
frequency (LOW).
g. Press the MENU key 3 times to return to normal sounder display.
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