NorthStar Navigation NorthStar 491 manual How echo sounding works

To prevent delays, it is critical that you first obtain a Return Materials Authorization (RMA) number before returning your unit to the factory. If you purchased your 491 through a dealer, to get an RMA number, call the dealer with the serial number. The 491’s serial number is located at the top of the unit.

The 491 should be shipped in a properly designed carton with packing material. Please reference the RMA number on the outside of the carton.

Shipments to Northstar should be made to the following address:

Northstar Technologies

30 Sudbury Road

Acton, MA 01720

If you have overnight or second-day shipping requirements, please call the Northstar factory for turnaround time and freight costs before shipping your 491.

How echo sounding works

An echo sounder produces high-voltage electrical pulses that the transducer converts into sound waves (called “pings”). The sound waves are sent downward through the water. When a sound wave hits and reflects off an object, such as fish, debris, seaweed, or the seabed, the reflected sound wave (an “echo”) returns back to the transducer along an imaginary vertical line called a “water column.” The transducer converts this echo into a tiny electrical pulse. The 491 digitizes these pulses and sends them to the navigator, so that echo sounding pictures of the water and seabed can be displayed and analyzed on the echo sounder screen. In essence, this system lets you see a real-time cross section of what’s happening underneath your vessel.

Figure 1, ”957/958 echo sounder system components,” below, and Figure 2, ”961/962 echo sounder system components,” below, show how the 491 connects to these navigators to enable echo sounding functions.

491 Echo Sounder Operations Manual Page 5