Lowrance electronic LCX-17M - Manual (Page 14)

6
How Your Sonar Works
Sonar has been around since the 1940s, so if you already know how it
works, skip down to read about the relatively new technology of GPS.
But, if you've never owned a sonar fish finder, this segment will tell you
the underwater basics.
Sonar is an abbreviation for SOund NAvigation and Ranging, a
technology developed during World War II for tracking enemy
submarines. (Lowrance developed the world's first transistorized
sportfishing sonar in 1957.) A sonar consists of a transmitter,
transducer, receiver and display. Here’s a simple explanation of how it
finds the bottom and the fish.
The transmitter emits an electrical impulse, which the transducer
converts into a sound wave and sends into the water. (The sound
frequency can't be heard by humans or fish.) The sound wave strikes an
object (fish, structure, bottom) and bounces back to the transducer,
which converts the sound back into an electrical signal.
The receiver amplifies this return signal, or echo, and sends it to the
display, where an image of the object appears on the scrolling sonar
chart. The sonar's microprocessor calculates the time lapse between the
transmitted signal and echo return to determine the distance to the
object. The whole process repeats itself several times each second.
Your sonar unit can record a log of the sonar signals that scroll across
the screen and save them to the MMC memory card. (These recordings
are also called sonar charts or sonar graphs.) You can replay this sonar
log in the unit using the Sonar Simulator function, or play it back on a
personal computer using our free Sonar Viewer. The viewer is available
for download from the Lowrance web site, www.lowrance.com.
You can save several different sonar log files, erase 'em and record new
ones, over and over again. The size of your sonar recordings are only
limited by the free space available on your MMC.