Simrad NX45 Specifications download pdf (Page 39)

Simrad NX40/45 Installation and Operation Manual 39

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 sh and may also create a double bottom trace.

See following for an example of the echosounder window

in such an environment. A double bottom trace is shown

on the window.

When looking for sh 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.

A Fish is visible on the window

B Fish is hidden by the strong echoes off the bottom

and is not shown on the window

9-3 Single and Dual frequency shnding

Sounder frequencies

The unit has two echosounder frequencies, 200 kHz and

50 kHz..

To select the echosounder frequency

> Frequency > 200 kHz or 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 denition 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 sh, 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 denition display with more

shadow compared to the 200 kHz frequency. This means

that a group of small sh, for example, could be shown

as a single item, while any sh very close to the bottom

may not be found at all.

Sounder window of same area

Example of shadows

1 2 ... 34 35 36 37 38 39 40 41 42 43 44 ... 119 120

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Simrad NX45 Specifications Page 39

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