42
However, in some situations, you may want to ignore
the sidelobe effect and increase the gain to achieve a
better display of the bottom far-forward of the vessel.
In general, Ultrascan PC90’s adjustable gain settings
help to minimize the sidelobe effect. This is because
each gain setting represents a time-varied-gain
(TVG) curve. These curves use lower gains for
earlier returns, which may include unwanted sidelobe
echoes, and higher gains for later returns which
include the desired echoes. Refer to page 30 for a
discussion of gain settings.
Interpreting the
Horizontal Display
In the horizontal scanning mode the Ultrascan PC90
scans from left to right across the vessel’s bow. The
forward scanning elements in the transducer are
positioned so that the plane of the horizontal scan is
angled downward approximately 10 degrees from the
water’s surface (see the diagrams at left and on p.21).
This downward angle is designed to help reduce the
effects of surface noise clutter when the water is
choppy and to allow easier mounting of the
transducer to the transom of smaller boats.
Imaging the Bottom
As the acoustic beam is projected away from the
boat, the cross-sectional area of the beam increases.
At a range of approximately 3 to 3.5 times the depth
of the water the sound beam will begin intersecting
the bottom and some of the sound energy that
intersects the bottom will be reflected back and will
appear on the Ultrascan PC90’s screen as bottom
echoes. Refer to the diagram at left.
It is important to understand that the Ultrascan PC90
will often see the bottom and will show it on the
forward display. This display information can be
used to help understand the structure of the bottom
ahead of the boat, but the bottom echoes can also
mask or be confused with other desired targets. In
the diagram at left, for example, a bait ball or school
of fish is lost in the bottom echoes. However, as the
vessel approaches the target, it will become distinct
from the bottom echoes as it moves into the nearer
Bait
200 ft Forward Range, Water Depth of 36 Ft
“False” Echoes Caused by Sidelobe Returns.
Summary of Contents for ULTRASCAN PC90
Page 1: ......
Page 5: ...5 Specifications 47 How To Obtain Service 51 9 Advanced Networking Information 48 Warranty 55...
Page 53: ...53 This Page for Notes...
Page 54: ...54 This Page for Notes...
Page 56: ...56...
