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Interference Rejection
- The Interference Rejection system is designed to knock out competing
return signals from other sonar units being used within proximity. When other sonar units are
causing interference to the display of the M3, activate the IR feature by depressing the IR key
located on the face of the M3. When you press the key, a beep will be heard. There are multiple
levels of interference rejection, and each press of the key will change the level of Interference
Rejection. The correct level of IR will be achieved when the display is clear of display clutter. In
some extreme cases, clutter will be greatly reduced but not eliminated. It is recommended that
only one person in a group adjust the interference rejection at a time.
Zoom
- The Zoom function can be activated by depressing the ZM key. An audible beep will
indicate that the Zoom function has been activated. The Zoom function divides the circular display
screen in half. The right half of the display, (12 to 6 o’clock on the dial) will become your entire
surface-to-bottom display. This will be indicated by a RED band of light at the top (zero) and a RED
band of light at the bottom (or 6 o’clock). If you are on the 20-foot depth range, the 12 o’clock
position will be the surface of the water and 6 o’clock will be the bottom of your chosen depth
range (20 feet on the 20-foot scale). When utilizing the Zoom function, you will be reading your
depth markings by viewing the inner circle (YELLOW numeric) located in the center of the M3
display dial. If you select the 40-foot scale, the same applies, except you multiply the YELLOW
numeric markings by 2. The 80-foot range setting is a multiple of 4, and the 160-foot range setting
is a multiple of 8. Once you use the M3 a few times, your brain will automatically make the adjust-
ment without any noticeable thought process. The backside of the display (6 o’clock moving
clockwise to 12 o’clock) is the other half of your split-screen display. This half reads what you see
on the right half, but in a magnified version. This will greatly enhance the precision of your presen-
tation and show that multiple smaller targets might exist on the left half (Zoom) where it appears
that one larger target is showing on the right (normal display). You can determine the size of your
Zoom window (the width or amount of water viewed within the water column) by depressing the
ZM key. If you depress the key once (turning Zoom ON), the window is 5 feet on the 20- or 40-foot
range setting, if you press the ZM key again the Zoom window is expanded to 10 feet. Depress the
ZM key again and the Zoom feature is turned OFF. The 80-foot range allows you a 10-foot viewing
window; depress ZM again and it will become a 20- foot Zoom window. The 160-foot range has a
20-foot window, or it becomes 40-foot when ZM is depressed again
Signal Interpretation
Hard-bottom readings (rock or gravel) will be displayed by a wide band of RED light indicating a
strong return signal. Conversely, a soft bottom (mud or silt) will return a weaker signal and will
result in a narrower RED band or possibly even a combined RED and GREEN band. A soft bottom
with weed growth will often appear as a narrow RED or GREEN band combined with both
solid and broken
ORANGE
segments indicating weeds. Any fish in the weeds may show as
RED or GREEN depending on fish size and relationship within the transmit beam (in the middle
or on the outside of the transmit signal).
Reading Fish
– Fish will generally appear as separate targets from the bottom. A fish target can
be displayed as RED, ORANGE or GREEN, depending on the size of the fish and the location
within the transmit beam. Larger fish located in the center of the beam (cone) can appear RED and
will be displayed as a wider band on the display. Smaller fish or fish on the outside of the cone may
appear ORANGE or even GREEN. Fish moving through the transmit beam may change color as
the return signal strengthens or weakens reflecting their location. Fish that are right on the bottom
can appear as part of the bottom. The best indication of a fish sitting right on the bottom is that the
leading edge of the bottom return signal is either ORANGE or possibly a dithering or flickering
RED segment. It is important that the GAIN or sensitivity be kept to a minimum when displaying a
strong bottom return.
