NorthStar Navigation Multi-Function Unit M84 - Manual (Page 38)

Northstar M121/M84 Installation and Operation Manual 37
A Narrow angle, more detailed 200 kHz cone
B Wide angle, less detailed 50 kHz cone
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.
When to use Mixed
The Mixed frequency combines the 200 kHz
and the 50 kHz echoes on one sonar window,
filling in detailed echoes in the centre of the
sonar cone.
When to use 50/200 kHz
Operating the Instrument at both 50 kHz and
200 kHz simultaneously on a split window 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 window
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
window (see section 9-4).
A
B