Single And Dual Frequency Fishfinding - Navman TRACKFISH 6500 Installation And Operation Manual

Shadows
Shadows are created around areas where the ultrasonic beam cannot 'see'. These areas include
hollows on the bottom or beside rocks and ledges, where the strong echoes returned off the rocks
obscure the weak echoes of the fish and may also create a double bottom trace. See following for
an example of the sonar display in such an environment. A double bottom trace is shown on the
display.
When looking for fish with the wide angled 50 kHz frequency, be aware of increased shadows. Use
the high frequency 200 kHz in areas that have rocks and ledges because this frequency reduces the
shadow effect considerably.
Example of shadows
A
B
A

8-3 Single and Dual frequency fishfinding

Sonar frequencies
The TRACKFISH has two sonar frequencies, 200
kHz and 50 kHz. To select the sonar frequency
to use:
1 Go to a sonar display (see section 9).
, select Frequency and
2 Press
select 200 kHz, 50 kHz,or Mixed.
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
34
A Fish is visible on the display
B Fish is hidden by the strong
echoes off the bottom and is not
shown on the display
NAVMAN
Sonar display of same area
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.
TRACKFISH 6500 Installation and Operation Manual
A
B
A