How Echo Sounding Works - NorthStar 490 Echosounder Operation Manual

Chapter 1 - Welcome
The Northstar 490 is covered by a two-year limited warranty
(see the Limited Warranty Policy at the beginning of this
manual) which, in summary, states that if the 490 is returned
to the Northstar factory by the owner or dealer during the
warranty period, Northstar will repair or replace, free of
charge, any part found to be defective due to faulty materials
or workmanship, if the 490 has been properly installed and
hasn't been abused. The only cost to the owner will be the
one-way shipping charges and any associated charges that
may be imposed by the dealer.
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 490 through a
dealer, to get an RMA number, call the dealer with the serial
number. The 490's serial number is located at the top of the
unit.
The 490 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 490.

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 490 digitizes these pulses and
sends them to the navigator, so that echo sounding pictures of
490 Echo Sounder Operations Manual Rev. B2 Page 1-5