Changing The Frequency Of Echoes - NorthStar Echo Sounder 491 Operation Manual

Manually
overriding
automatic mode

Changing the frequency of echoes

491 Echo Sounder Operations Manual
You can always manually change any of the echo sounder's
settings: the gain, clutter, noise limiter, shift, and range.
Changing the appearance of the picture (colors, gain, clutter,
and the noise limiter) is described in Chapter 3.
Setting the range and shift is described in Chapter 6.
The 491 uses two transducer frequencies: 50 kHz and 200
kHz. The advantages and disadvantages of each frequency are
shown below.
Table 2: 50 kHz vs. 200 kHz
50 kHz
Longer wavelength goes deeper,
but with somewhat lower resolu-
tion.
Less resolution is better at finding
big fish, but may miss the bait
fish.
Wider beam is good for seeing
fish not directly beneath the boat.
You can choose from four settings for the transducer
frequency:
• 50 kHz displayed on a full screen
• 200 kHz displayed on a full screen
• 50 kHz on the left half of the screen, and 200 on the right
• 200 kHz on the left half of the screen, and 50 on the right
There are two reasons why you might want to operate with
your preferred frequency on the right side of the screen:
• the zoom function magnifies the frequency on the right
side
200 kHz
Shorter wavelength provides a
sharper picture, but can't go as
deep.
Finer resolution is better at find-
ing small fish (baitfish) and subtle
bottom details.
Narrower beam is very focused.
Reduces the influence of a rough
sea.
Page 17