NorthStar Navigation Explorer 660 - Manual (Page 34)

Northstar Explorer 660 Installation and Operation Manual 34
Sonar frequencies
The Explorer 660 has two sonar frequencies, 200
kHz and 50 kHz. To select the sonar frequency to
use, set Frequency (see section 15-3).
When to use 200 kHz
The 200 kHz frequency is especially suitable for
use in shallow and medium depth water, typically
less than 500 ft (150 m) and while running at
speed.
At 200 kHz, the narrow cone reduces any noise
caused by air bubbles.
The 200 kHz frequency generates a higher definition
pulse which produces little shadow and returns
excellent detail over a small area of bottom.
Therefore, it gives excellent bottom discrimination
capability and is particularly good at showing
individual fish, including bottom dwellers.
When to use 50 kHz
The 50 kHz frequency is particularly suitable for use in
deep water, typically greater than 500 ft (150 m).
At 50 kHz, the cone covers an area of water about
four times wider than the 200 kHz cone and
penetrates to a greater depth with minimal loss of
the return signal.
However, it produces a lower definition display
with more shadow compared to the 200 kHz
frequency. This means that a group of small fish,
for example, could be displayed as a single item,
while any fish very close to the bottom may not
be found at all.
This frequency is useful for getting a deep, wide
overview of the area so that any areas of interest
can be identified and then examined in detail
with the 200 kHz frequency.
Wide angle,
less detailed
50 kHz cone.
Narrow angle,
more detailed
200 kHz cone.
8-3 Single and Dual frequency fishfinding
When to use Mixed
The Mixed frequency combines the 200 kHz and
the 50 kHz echoes on one sonar display, filling in
detailed echoes in the centre of the sonar cone.
When to use 50/200 kHz
Operating the Explorer 660 at both 50 kHz and
200 kHz simultaneously on a split display can be
very useful when operating in shallow to medium
water, typically less than 500 ft (150 m), because
the 50 kHz section of the display shows the
general area, while the 200 kHz section can be
viewed simultaneously for a more detailed look at
any interesting feature.
To use 50/200 kHz, select the Split 50/200 display
(see section 9-4).