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491 INSTALLATION MANUAL Revision A PAGE 27
APPENDIX A — Technical specifications
Table 8: 491 technical specifications
Performance characteristics
Frequencies 50 and 200 kHz
Output power 1000 watts with dual-element transducers
600 watts with single-element transducers
Pulse lengths 0.1 to 2 ms
Pulse repetition rate 30 to 600 pulses/min
Alarms Fish, bottom, and temperature
Update rate 10 Hz maximum (depends on water depth)
(up to 20Hz when used with the Northstar
6000i)
Zoom modes Marker, bottom lock, bottom lock/center,
bottom
Auto modes Fishing or cruising
Navigation data Shown on bottom of screen
Display modes Single/dual frequency, split-screen, four
zoom modes, A-Scope
Physical characteristics
Dimensions 8.78 x 7.22 x 2.35 inches (including back-
plate)
Weight 2 pounds
Environmental characteristics
Temperature -25˚C to +60˚C operating temperature
-55˚C to +90˚C storage temperature
Standards Waterproof, sealed design meets the follow-
ing: EN60529 IP65; EN60945 emissions; CE
Electrical characteristics
8 to 36 VDC, 8 watts, reverse polarity and
overvoltage protection
Transducer outputs protected against open
circuit/short circuit