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INTERPRETING SIGNALS
DIGITAL DEPTH
— The digital depth display on the MarCum Digital Sonar provides a quick and
easy way to determine depth. Digital Depth is always displayed in the center of the circular
display, and on the bottom of the vertical displays. It will also show in the upper left corner of the
graph in some configurations. This display can be used as a quick reference when checking
depths through the ice.
READING BOTTOM
— When interpreting your bottom signal, always read the leading edge
(shallowest side) of the signal return. If you have a strong signal return (wide band) and it starts
at 13 feet and ends at 16 feet, the correct depth is 13 feet or the shallowest leading edge of the
return signal. Anything beyond the shallowest leading edge indicates the strength of the return
signal.
The MarCum Digital Sonar can also be used to determine bottom composition. The thicker and
bolder your bottom shows, the harder the bottom is. In some cases, hard bottom can be
indicated by a “double” or second echo that will show on your display at approximately twice the
water depth. Soft bottom (silt, mud, muck) will only register one bottom reading.
Using your Sonar in conjunction with an underwater viewing system is a great way to learn how
to interpret your sonar signals.
READING FISH
— Fish will generally appear as separate targets from the bottom. Depending on
the size of the fish and the location within the transmit beam they can show as any of the colors
in the palette you are using. RED indicates the strongest signal on all the color palettes, and this
generally indicates a fish directly below the transducer. Smaller fish or fish on the outside of the
cone may appear orange, yellow, or even green or blue. Fish moving through the transmit beam
may change color as the return signal strengthens or weakens reflecting their location.
Some fish, like walleyes, are notorious for cruising right on the bottom. The Marcum Digital
Sonar has target separation fine enough that it will generally show bottom hugging fish as a
separate signal. However, 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 a thin band of a color other than red, possibly dithering or flickering. It is important that
the sensitivity be kept to a minimum when displaying a strong bottom return. Having your
sensitivity too high will flood out the ability to differentiate targets and clutter the display.
Utilizing the ZOOM feature can give you a magnified look at the bottom when this is happening,
and help you better learn what is going on below you.
Schooling fish, like panfish, will sometimes group in large numbers suspended off the bottom. A
big school of fish concentrated in one portion of the water column can show on your sonar as
one large “blob”, and it can be difficult to pick out individual targets. Zooming in on the zone with
the most fish will give you better definition and switching to the 8-degree cone will eliminate
signals from fish on the periphery of your area, improving your definition even more.
READING LURES AND JIGS
— The MarCum Digital Sonar will pick up and display the smallest
of lures and jigs. When tuning the unit to display your lure, lower it to the desired depth and turn
up the SENS until you see the lure or bait on the display. It is important that the SENS be set so
it displays the lure or bait as you raise or lower it. Once you have the SENS set where you want
it, you can fine- tune your signals by using the TARGET ADJUST button.
NOTE:
When tuning the unit to display lures or bait, make sure that the objects are in the center
of the hole and therefore in the center of the transmit beam. If there is current (some lakes and
all rivers have under water current or movement) and the lure doesn’t weigh much, it may move
to the outer edge of the signal or out of the transmit beam altogether.
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