NorthStar Navigation NorthStar 491 manual Changing the frequency of echoes, kHz 200 kHz

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Manually overriding automatic mode

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.

Changing the frequency of echoes

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	200 kHz

Longer wavelength goes deeper,	Shorter wavelength provides a
but with somewhat lower resolu-	sharper picture, but can’t go as
tion.	deep.

Less resolution is better at finding	Finer resolution is better at find-
big fish, but may miss the bait	ing small fish (baitfish) and subtle
fish.	bottom details.

Wider beam is good for seeing	Narrower beam is very focused.
fish not directly beneath the boat.	Reduces the influence of a rough
	sea.

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

491 Echo Sounder Operations Manual

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Contents Northstar Echo Sounder Contents Troubleshooting 491 Operations Reviewing past echoes using SoundTracPage 1Welcome Using this manual Welcome to the NorthstarOrganization Conventions Service and repair Technical supportHearing from you How echo sounding works 961/962 echo sounder system components Powering the 491 on and off Setting upUsing 491 with the 961/962 Press the Port Setup Options key Using the 491 with the 957/958961/962 echo sounder menu structure 957/958 echo sounder menu structure 2Quick Start Using the Echo Sounder Illustrated Echo screen Displaying the echo sounder’s pictureIllustrated Soundtrac screen Using demo mode At the Chart Overlay Selection window, pressChart Overlay screen Introducing the displayed information Depth and temperatureEcho sounding Navigation Status tabsCruising or ﬁshing Using automatic modeManually overriding automatic mode Changing the frequency of echoes50 kHz 200 kHz Echo screen with both frequencies displayed Choosing a zoom mode Zooming in and outChoosing the zoom scale Using bottom lock zoom Using bottom zoomUsing bottom lock/ center zoom Accessing the setup screen Setup functionsEntering numerical values Transducer depth Changing the temperature graph’s units and scaleChanging the depth units Number of special waypoints961/962 sensor setup screen Speed and temperature sensor setup957958/ sensor setup screen 3Adjusting the Echo Sounder Picture Picture menu Adjusting the gain strong echoesGain window Adjusting the clutter weak echoesClutter window Adjusting the signal level weak echoesSuppressing interference the noise limiter Understanding the color bar Selecting the color bar hue and white levelHue and white level window Setting the white levelEcho Sounder Operations Manual 4Understanding Depth Settings Changing the depth settings Viewing the seabed depthViewing the depth marker Shift window Setting the picture’s shift starting depthSetting the picture’s range Range window Echo Sounder Operations Manual 5Other Functions Using the More key Changing the advance speed Using the More keyScope on single-frequency echo screen Displaying the A-scopeSetting the Echo screen data Using the A-scope with dual frequenciesScope on dual-frequency echo screen Echo screen data selections Bottom depth box Temperature boxIntroducing snapshots Temperature graphSpeed through the water Taking and storing a snapshotSnapshot screen 961/962 only Archiving and restoring a snapshot with a ﬂoppy diskArchiving snapshots screen 961/962 only Archiving and restoring snapshots with a Zip diskSetting up the video image overlay Echo Sounder Operations Manual 6Reviewing past echoes using SoundTrac SoundTrac screen Viewing past echoes using SoundTracNavigating to a past echo position Marking ﬁsh as waypointsSelected Cursor Position window appears Going directly to a past echo position7Setting the Alarms Setting the ﬁsh alarm Understanding the alarmsFish alarm window Setting the upper and lower marker depthsSetting inside or outside ﬁsh markers Setting the bottom alarmAlarm Turning the ﬁsh alarm on and offBottom alarm window Setting the bottom levelSetting the temperature alarm Turning the bottom alarm on and offTemperature alarm window Upper limit window is highlighted in black Turning the temperature alarm on and offWhen the temperature alarm sounds, an alert message is Troubleshooting the echo sounder Checking the transducer 8Troubleshooting 491 OperationsNo echoes displayed when Star key is pressed Troubleshooting the echo sounderOFF Checking the transducerMaintaining a transducer Manufacturer Model Power Northstar P/NPerformance characteristics A491 Features and SpeciﬁcationsEnvironmental characteristics Physical characteristicsScreen notations InterfacingON/OFF Manual controlsEcho Sounder Operations Manual Glossary Echo Sounder Operations Manual