NorthStar Navigation Multi-Function Unit M84 - Manual (Page 42)

Northstar M121/M84 Installation and Operation Manual 41
9-6 Gain and threshold
Gain and threshold settings control the amount
of detail displayed on a sonar window:
Gain: The gain of the sonar receiver. The gain
should be high to display good detail, but if
the gain is too high then information from the
strong bottom signal is lost and false echoes
might be displayed. There is a separate gain
setting for each sonar frequency, 50 kHz and
200 kHz.
Threshold: Return echoes less than the
threshold are ignored. The threshold should
be as low as possible, but if the threshold is
too low, unwanted noise will be displayed.
Threshold is set as a percentage of gain. For
example, if the threshold is 50 %, then return
echoes less than 50 % of the maximum signal
are ignored. There is a separate threshold
setting for each sonar frequency, 50 kHz and
200 kHz.
The gain window
To display or change the current settings for
gain, select a sonar window and press
ENTER
.
Select Threshold to display the thresholds.
Changing mode
This window is called the gain window.
The Instrument has three operating modes, In
Cruising and Fishing modes, the Instrument
automatically adjusts gain and threshold for
good performance. In manual mode, you can
hand adjust the settings.
To change the mode from the Gain window,
Select Mode and then select Fishing,
Cruising or Manual. When you select
Manual, the Instrument reverts to your last
manual settings.
Changing gain and threshold
1 In the Gain window, press or to select
the setting to adjust.
2 Press or adjust the setting. The
Instrument changes to Manual mode.
Tip: Use the A-scope window to help set
gain or threshold manually (see section
10-5).