NorthStar Navigation EXPLORER 435 - Manual (Page 20)

Northstar Explorer 435/438 Installation and Operation Manual 20
Transducers Installation Guide).
• If the boat is anchored then fish will tend to
show on the display as horizontal lines as they
swim into and out of the transducer sonar
beam. Slow speeds in deeper water give the
best fish arch returns.
• Range is important. It will be much easier to
see fish arches when using zoom mode to
concentrate on a particular section of water,
rather than just displaying everything from
the surface to the bottom. Zooming increases
screen resolution up to 100 times.
• It is difficult to get fish arches in shallow water
as the transducer sonar beam is very narrow
near the surface and fish do not stay within
the beam long enough to display an arch.
Several fish in shallow water tend to display as
randomly stacked blocks of pixels.
• Wave motion may result in distorted fish arches.
Fish arches
In good conditions and with Fish symbols Off, a
fish passing through the cone-shaped ultrasonic
pulse is displayed as a fish arch.
A fish arch occurs when a fish enters the weak
edge of the sonar cone, generating a weak echo
that is displayed as the first pixel of the fish arch.
As the fish moves closer to the middle of the cone,
the distance between the transducer and the fish
reduces and the echo is displayed at progressively
shallower depths, producing the start of an arch.
When the fish passes directly beneath the middle of
the cone, the echo becomes strongest and thickest.
As the fish passes out of the middle of the cone the
reverse happens with a progressively weaker and
deeper echo.
There are many reasons why fish arches may not
be seen. For example:
• Poor transducer installation (see Transom
4-3 Gain
Gain (sensitivity) controls the amount of detail
displayed on the Explorer 435 and Explorer 438.
Understanding how to set suitable Gain settings
is important for optimum performance.
The Northstar fishfinder has two gain modes,
Auto Gain and Manual Gain. Normally the
best results are obtained in Manual Gain, but
practice and experience are required to obtain
the optimum settings for different conditions.
Therefore, the use of Auto Gain is strongly
recommended when learning to use the
fishfinder or when travelling at speed.
• In Auto Gain, the gain adjusts automatically to
compensate for water depth and clarity.
• In Manual Gain, the gain can be adjusted by
the user to compensate for water depth and
clarity.
High Gain settings may amplify the normal
background noise until it appears as random
pixels.
Changing between Auto and Manual
To change between Auto Gain and Manual Gain:
1. From any Sonar display, press .
2. Use the cursor key to select Auto or
Manual.
Adjusting Gain settings
1. From any Sonar display, press .
2. Use the or cursor keys to change the gain.
Unwanted
signal
Gain
Threshold
line
Gain line
Note: The Gain mode
automatically changes to
Manual Gain if the gain
setting is adjusted by
the user.
Obtaining the
best results
To obtain the best
detection capability for
both fish and bottom
we recommend the user adjusts the gain in the
A-Scope display until the threshold line is just to
the right of the unwanted noise: