USING THE 250DX
HOW SONAR WORKS
6
HOW SONAR WORKS
Your Humminbird unit uses sonar to
locate and define underwater objects,
define the bottom terrain, as well as
determine distance.
Sonar technology is based on sound
waves. Your Humminbird unit sends
out a sound wave signal. With this
signal it determines distance by
measuring the time between the
transmission of the sound wave and
when the sound wave is reflected off
an object. Your Humminbird uses the
reflected signal to interpret location,
size and composition of an object.
Sonar is very fast. A sound wave can travel from the surface to a depth of
240' (70m) and back again in less than
¹⁄₄
of a second. It is unlikely that
your boat can "outrun" this sonar signal.
The 250DX is a dual frequency, dual beam unit, and generates two distinct
sonar signals - one narrow, one wide. Each signal is optimized for a
particular purpose. First, the center beam transmits at a frequency of 200
kHz in a 20 degree (narrow) symmetrical pattern for greater depth
capability and excellent detail. Information from this center beam is used to
draw the graphic representation of the bottom on the display.
Second, the wide beam transmits at a frequency of 83 kHz in a 53 degree
(wide) symmetrical pattern for greater area of coverage. Information from
the wide beam is used to accurately detect the presence and location of
fish. A wide beam has a large area of coverage but limited resolution of
detail. A narrow beam has excellent detail, but within a limited area
of coverage.
The combination of the two beams and dual frequencies provides the
combination of a large area of coverage and a high level of detail.
