The Northstar echo sounder system consists of: • the Northstar 491 echo sounder sensor • a Northstar navigation system such as the 962, 958 or 6000i • a transducer The 491 can be used with either a single-element transducer or a dual-element transducer. The 491 automatically pings both transmitters at power-up to determine the number of transducer elements connected. If a single element is detected, the 491 operates in single-frequency or dual-frequency interleaved mode (as determined by the ope