Furuno Marine Radar - Manual (Page 21)

Navigate straight to waypoint •
The map-like picture displayed by Radar helps you
navigate straight to a waypoint and compliments chart
plotter images.
Receive Radar beacon (RACON) •
Radar can receive pulsed signals from a Radar beacon
to determine own ships position.
Fishing operation •
Besides its basic function as an aid to navigation,
Radar is also a valuable tool for fishing operations.
Purse seiners use it to monitor net shape, observing
the echoes from floats attached to the net. It is
especially useful in fleet fishing for determining
position of vessels, locating fishing grounds and
positioning vessels.
Specialty fisherman use Radar to search for sea birds,
which may be an indication of the presence of bait
fish or their target species. This technique has become
easier with the advent of dual-range simultaneous
scanning, such as that found in NavNet 3D, where
the navigator can use one Radar screen with the gain
set for targeting birds, while the other Radar screen
is used to navigate. As you can see, for many fishing
vessels Radar functions more often as an aid to fishing
rather than an aid to navigation.
How It Works
Did you ever shout at a cliff and hear the echo of your
shout? Radar works in a similar manner. Imagine that
radio pulses are emitted from the scanner in a certain
direction. When the pulse strikes an object such as
a ship or island some of the energy returns to the
scanner. The direction in which the scanner is pointing
when the reflection is received is the direction of the
target causing the reflection. Since radio waves travel
at a near-constant speed, the time required for the
reflected echo to return to the scanner is a measure of
the range to the target.
How Radar determines range
The radio pulse makes a complete round trip, but
only half the time of travel is needed to determine the
range to the target. This equation shows how range is
determined:
D = 1/2 x cT
c = Speed of Radio Pulse (3 x 108 m/sec)
T = Time between transmission of radio pulse and
reception of reflected echo
D = Distance
Both radio waves and light travel at the near-constant
speed of 186,000 miles per second; therefore, the
Radar can process vast amounts of information in
a very short time. Comparatively, Sonar and Fish
Finders use ultrasonic waves rather than radio waves.
Since the propagation speed of the ultrasonic wave
is 1,500 miles per second, signal processing is much
slower with these devices than with Radar.
How Radar determines bearing
Radar determines the range to a target by measuring
the amount of time required for a reflected echo to
return to the scanner. Bearing to a target is determined
by the direction from which a reflected echo returns.
The scanner rotates 360 degrees about its vertical
axis, using a special gear. In order to achieve precise
bearing resolution the antenna radiates RF (radio
frequency) power in the form of a highly directional
beam. “Super” beams having horizontal beamwidth
on the order of one 1 degree or less provide highly
precise bearing information. The sharper the beam,
the more accurately the bearing of a target can be
determined.
How the Radar displays targets
Radar targets are displayed on what is called a Plan
Position Indicator, or PPI. This display is essentially
a polar diagram, with the transmitting ships’ position
at the center. Images of target echoes are received
and displayed at their relative bearing, and at their
distances from the PPI center. Early model Radars
displayed targets and possess few features such as
heading marks and range rings. To view the display,
a viewing hood was required to block out extraneous
light.
Radar FAQ’s continued ...
Q: What are Radar side lobes and what do they do?
A: Side lobes are naturally occurring areas of transmitted energy that are part of virtually any transmitter used
in marine electronics. Radar, echo sounders (fishfinders) and sonars all generate a “main beam”, which is also
known as the “main lobe”. “Side lobes” are transmitted energy that is outside of the “main beam” or “main
lobe”.
Reflections from side lobes can sometimes cause false targets and/or “noise” on your display. All Furuno
products have gain and clutter controls to help minimize the affects of side lobe returns. Many installation
menus and settings exist for fine-tuning Furuno products.
Q: Why does my Radar have to wait 2 minutes after I turn it on before I get a picture?
A: The component that transmits Radar energy is called a magnetron and is similar to that which is in your
microwave oven, but much more powerful. This is a tube, which will be damaged if the filament isn’t heated to
a proper temperature. Therefore, Radars have a timing circuit – typically 2 or 3 minutes – which disables the
magnetron from transmitting until the filament is sufficiently heated. This protects the magnetron from being
damaged.
Additional Resources
www.FurunoUSA.com:
Visit our web site at www.FurunoUSA.com for information on the entire
line of award-winning Furuno Radars. Browse through our catalog of
chart plotters, fish finders, sonar, communication products and PC soft-
ware to round out your helm.
Furuno Support Center:
Have a question that needs an answer? Click on support and browse
through our extensive library of frequently asked questions. You can
also ask our knowledgeable Technical Support staff a question and
receive an answer via e-mail.
Authorized Furuno Dealers:
Your local Furuno dealer is a valuable resource when it comes to an-
swering specific questions about the electronics that are right for you.
To find your nearest Furuno dealer, simply go to our web site at www.
FurunoUSA.com and click on Dealer Locator. Enter in your zip code and
you will receive a complete list of Furuno dealers in your area.
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