Furuno Marine Radar User Manual
Operator’s Guide to
Marine Radar
Table of Contents
© Copyright Furuno USA 2008
All Rights Reserved
1-3) Principles of Radar
3-5) Radar System Congurations
5-6) Radar Terminology
6-8) Radar Controls
9) Targeting Birds
10-11) Range, Bearing and Position
12-14) Advanced Radar Operation
15-18) Radar FAQ's
19) Additional Resources
20) Radar Mark Denitions
21) Maintenance
Boats of all types can benet from having a Radar
onboard for navigation and situational awareness..
When it comes to safety on the water, no other piece of
electronic equipment on your bridge is as important
as your Radar. For more than 30 years, Furuno Radars
have consistently won the prestigious NMEA (National Marine Electronics Association) award for Best Radar. Whether you are looking for a compact 2.2kW unit
or a commercial grade 50kW Radar, Furuno is the single largest source of Radars you can rely on. This book
will help you learn about what a Radar is, how it works,
and how to get the most from what is perhaps the most
important navigation device you will ever own.
1. Principles of Radar
What is Radar?
Radar is an acronym meaning RAdio Detecting And
Ranging. It is a device which measures not only the
time it takes for a pulsed signal to be reected back
from an object but also its bearing relative to your
position. No other piece of marine electronics can give
you as much information about objects around your
own ship as Radar.
Present state of Radar:
Radar was developed during World War II. Today,
Radar is available for all classes of vessels including
small shing vessels and pleasure craft. Many
pleasure boats may also have a color video sounder
(Fish Finder) or navigation device such as a GPS
receiver, but the single most important piece of
electronics is the Radar. No other gear can give you
the ability to spot a vessel coming at you out of the
fog, or tell you the location of the inlet to a harbor in
the pitch black of night.
For navigational safety, nothing beats Radar. While
your chart plotter may show you where everything
around you is supposed to be, only your Radar can
show you where everything is, including coastline
and navigation aids such as beacons or buoys, as well
as uncharted objects such as vessel trafc and other
obstructions.
About Furuno Radars:
The National Marine Electronics Association (NMEA)
annually recognizes its member marine electronics
manufacturers for superior products. Furuno annually
takes home the top award in several categories of
marine electronics equipment, and our Radars have
won the top prize every year since 1976. Furuno
has repeatedly won the coveted NMEA award for
Manufacturer of the Year - Support. These awards
make it clear that Furuno is the leading manufacturer
of Radar in terms of quality, reliability and after-
purchase support.
What Radar Can Do
Radar mainly functions as an anti-collision aid. It
also provides information about the whereabouts of
neighboring vessels, coastal outlines, etc.
Navigate in darkness and fog•
In fog or darkness, you may lose situational awareness
around your own ship because of poor or no visibility.
With Radar acting as your eyes, however, you have
the ability to monitor other ships’ movement under
these conditions.
Collision avoidance•
The guard alarm feature of every Furuno Radar alerts
you when targets enter a particular area, or own ship is
nearing a danger area. The alarm area can be forward
of own ship or a 360-degree circle around the vessel.
When Radar targets such as other ships, landmasses or
buoys enter the zone, an audible alarm sounds to alert
the operator.
Assess target movement•
The Echo Trail feature simulates target movement
in afterglow. It is useful for assessing the movement
of all targets relative to own ship. Some Radars have
the capability to show the true movement of targets,
providing increased navigational safety.
Determine own ships position•
Since Radar sees further than the naked eye, the
echoes from islands and landmasses can be used to
determine own ships’ position. When running near
land, you can use peninsulas and other targets whose
echoes show distinct contours on the display to
determine own ships’ position. Distant, tall mountains
or bridges may be similarly used provided they are
above the horizon
Navigatetospeciclocation•
Fishing vessels and pleasure boats use Radar to
help them navigate to favorite shing spots. When
navigating to a shing spot, the forces of wind
and current can combine to throw the vessel off its
intended course. To remember your location if your
ship drifts, use the VRM and EBL to mark range and
bearing to nearby islands or peninsulas.
120
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 shing operations.
Purse seiners use it to monitor net shape, observing
the echoes from oats attached to the net. It is
especially useful in eet shing for determining
position of vessels, locating shing grounds and
positioning vessels.
Specialty sherman use Radar to search for sea birds,
which may be an indication of the presence of bait
sh 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 shing
vessels Radar functions more often as an aid to shing
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 reection is received is the direction of the
target causing the reection. Since radio waves travel
at a near-constant speed, the time required for the
reected 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:
2
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 reected 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 reected echo to
return to the scanner. Bearing to a target is determined
by the direction from which a reected 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.
Almost all late model Radars use Liquid Crystal
Display (LCD) or daylight bright Cathode Ray
Tube (CRT) displays. These types of displays
provide steady, bright, non-fading Radar echoes
in monochrome or color depending on model.
The picture is visible even in full daylight. Digital
information is displayed on-screen to keep you
informed of your navigational situation at all times.
Radar range
Atmospheric conditions and target shape, material and
aspect slightly affect Radar range. However, Radar
range is generally calculated as follows:
RadarSystemConguration
Basic system
The basic Radar system consists of two units: the
scanner unit and the display unit. The transceiver
(transmitter/receiver unit, or t/r) is generally housed
in the gearbox of the scanner unit. In some designs
the t/r is separate from the scanner unit and contained
in its own housing; such a unit is referred to as ‘t/r
down.’ Also, the control unit may be separate from
the display unit so as to allow for custom selection of
display in what is referred to as a ‘black box’ system.
Figure 1 - Determining Radar range
D is the distance from the scanner to the target
horizon. Under normal atmospheric conditions, this
distance is 6% greater than the optical horizon. This
is because radio waves bend or refract slightly by
atmospheric change.
The higher the scanner or target is above the surface,
the longer the detection range. For example, if the
scanner is 9 meters above the sea surface and the
height of the target is 16 meters, you should be able to
see the target’s echo on the display when the target is
15 miles from the Radar.
Unusual propagation conditions
Air ducts created by atmospheric conditions can affect
radio pulse propagation and thus Radar range. When
the radio pulse is bent downward, radio pulses can
travel great distances thereby increasing the ranges
at which targets can be detected. This is called super-
refraction. The opposite condition, in which Radar
waves bend upward and decrease the range at which
targets can be detected, is called sub-refraction.
Figure 2 - Basic Radar system
Scanner unit components
Most scanner units employ the circuits and devices
shown in Figure 3:
Figure 3 - Circuits and devices of a scanner unit
Magnetron
The magnetron generates the radio pulses.
Magnetrons, as well as the Radar itself, are classied
by their transmitting frequency band. There are two
main frequency bands in commercial Radar: X-Band
(9,000 MHz band; wavelength 3cm) and S-Band
(3,000 MHz band; wavelength 10 cm). Magnetron
output power ranges from 1kW for small Radars to
60kW for large Radars. Table 1 compares the S-Band
and X-Band frequencies.
Table 1 - Comparison of X-Band and S-Band
Frequency Band Characteristics
X-Band
S-Band
Short wavelength for better •
directivity
Attenuation in precipitation is •
greater than on S-Band
Small, light-weight antennas•
Longer wavelength for long •
range detection
Penetrates precipitation for •
excellent performance in
inclement weather
Large antenna•
Modulator
The device responsible for monitoring the magnetron
for proper operation is the modulator. It ensures that
the magnetron transmits at exactly the same frequency
throughout the duration of the pulse, and that the time
between pulses is the proper length.
TX/RX Switching
A TX/RX switching device enables the Radar to
transmit the radio pulse and receive its reected echo
through one scanner. The switching device used by the
Radar is called a circulator It consists of a permanent
magnet and a ferrite core. When transmitting, it
directs radio pulses to the scanner and disconnects
the receiver circuits. When receiving, it funnels weak
reected echoes away from the magnetron to prevent
both ow to the magnetron and loss of receive signal.
The length of the array affects horizontal beamwidth,
and thus the Radar’s ability to determine target
bearing. The longer the array, the more accurately the
Radar can determine bearing. For example, an array
of 50 cm length gives a horizontal beamwidth of 5
degrees, while one of 300 cm length gives a horizontal
beamwidth of 0.75 degrees.
Scanner directivity is a measure of the two
beamwidths. One is in the horizontal plane, known as
horizontal beamwidth, and the other is in the vertical
plane, known as vertical beamwidth. The narrower
the horizontal beamwidth the sharper the beam. The
vertical beamwidth should be wide; it is typically 20
to 25 degrees. The main reason for a wide vertical
beamwidth is to ensure the ability to display a target
while own ship is pitching and rolling.
Limiter
The limiter protects the receiver circuits from damage
in the event own ship’s Radar receives radio pulses
from another ship’s Radar. When this occurs, the
limiter attenuates them to protect the next stage MIC
(Microwave Integrated Circuit).
MIC
MIC is an acronym meaning Microwave Integrated
Circuit. The MIC consists of a local oscillator and
mixer circuits. Incorporating those devices on an IC
improves quality, reliability, sensitivity and noise
gure (nf).
Scanner
The scanner transmits the radio pulses and receives
their reected echoes. Most scanners rotate at a
constant speed of 24 rpm. Many modern Furuno
Radar scanners rotate at variable speeds dependent
upon the range in use in order to optimize Radar
detection. The type of scanner used by most vessels
is the slotted array, an antenna with a series of slits
spaced at suitable intervals and angles from which
radio pulses are transmitted. The reected echoes also
pass through these slits.
Figure 4 - A typical slotted array scanner
IFAmplier
The IF amplier amplies the Intermediate Frequency
signal output by the MIC.
Display unit components
Most display units employ the devices shown in
Figure 5:
Figure 5 - Devices of a display unit
4 17
A/D Converter
The received IF signal is an analog signal. This signal
is converted to a digital signal in order to undergo
various processing in the display unit. The A/D
(Analog to Digital) converter converts analog signals
to digital signals.
Signal Processing
This section is the heart of the Radar and contains
computers, memories, and other IC’s. Extensive use of
digital techniques permits high speed processing.
Control Unit
The control unit contains various keys and controls for
adjustment of the Radar picture. Whenever a control
setting is changed the associated reaction appears
almost immediately on the display. In some Radar
designs, the control unit is separate from the display
unit.
Range resolution is a measure of the capability of the
Radar to display as separate pips the echoes received
from two targets that are on the same bearing and
are close together. The main factor that affects range
resolution is pulselength. A short pulselength gives
better range resolution than a long pulselength.
Figure 7 - Example of range resolution
Basic Radar Terms
Radar Resolution: Different than display
resolution, which is a measure of the pixels in an LCD
display, Radar resolution describes the Radar’s ability
to distinctly display two Radar targets which are
close to each other. Radar has two types of resolution:
range, and bearing.
Bearing resolution is a measure of the capability of
the Radar to display as separate targets the echoes
received from two targets that are at the same range
and close together. The principal factor affecting
bearing resolution is horizontal beamwidth. The
narrower the horizontal beamwidth the better the
bearing resolution.
Generally, use a short pulselength on short ranges for
better range resolution, and a long pulselength on long
ranges for longer range detection.
Beamwidth: Beamwidth is the angular width,
horizontal or vertical, of the path taken by the Radar
pulse. Horizontal beamwidth ranges from 0.75 to
5 degrees, and vertical beamwidth from 20 to 25
degrees.
Figure 6 - Example of
bearing resolution
Figure 8 - Example of
scanner beamwidth
Pulse Repetition Rate: Pulse repetition rate is
the number of radio pulses transmitted in one second.
It is automatically determined by pulselength and
detecting range. For short ranges, pulselength is short
and the pulse repetition rate is high. For long ranges,
pulselength is long and the pulse repetition rate is low.
Minimum detectable range: This is the
minimum range at which a target is detectable by the
Radar. It is determined by scanner height, vertical
beamwidth, blind sector within the scanner beam, and
pulselength.
Maximum detectable range and output
power:
Radar raises the maximum detectable range by only
19 percent. In the reverse case, halving the output
power lowers the maximum detectable range by
16 percent. While you can increase the maximum
detectable range by using a high output power Radar,
a better (and more economical) way to do it would
be to mount the scanner as high as possible above the
waterline and/or utilize a longer antenna to increase
horizontal beamwidth.
Doubling the output power of a typical
Control Description:
Power: Powers the entire Radar system. After
turning on the power, a timer displays the time
remaining for transmission preparation. “ST-BY”
appears when the Radar is ready to transmit. The
method of turning off the power varies by model;
consult your Operator’s Manual for details on
powering off your Radar.
Economy: The economy mode turns off power to
the display in stand-by to lessen power consumption.
Trackball/Cursor Pad: The trackball or cursor
pad shifts the cursor, which sets the guard zone,
displays range and bearing to a target, etc. Some
models may have individual arrow keys in place of a
trackball or cursor pad.
Scanner: This switch starts and stops scanner
rotation. Turning the switch off when transmitting
sets the Radar in stand-by. A rotating scanner can be
dangerous - before turning the switch on, be sure no
one is standing near the scanner unit.
2. RADAR CONTROLS
This section briey describes the function, objective
and usage of Radar controls. Note that some controls
described here may not be provided on your Radar.
For detailed control description, refer to your
Operator’s Manual.
Precautions:
A rotating scanner is dangerous. Before turning the
Radar on, be sure no one is near the scanner unit.
The scanner unit emits high frequency radio pulses,
which can be harmful, particularly to your eyes. Never
look directly into the scanner unit when the Radar is
in operation.
Key response: The Radar normally releases a
beep when you correctly enter a command. If no beep
is released, try again. Incorrect command generates
several beeps. This function can usually be disabled,
but caution must be used as this audible feedback is
important to verify correct entry of commands.
ST BY/TX: Press this key to transmit radio pulses.
To stop transmitting, press the key again.
Gain: This control adjusts receiver sensitivity. Adjust
the gain to increase sensitivity and display echoes. For
long range, adjust the control so background noise
is just visible on the display. For short range, some
Radar operators set this control relatively high and
adjust sensitivity using the A/C SEA control.
A/C Rain (FTC): The Rain control, also called FTC
(Fast Time Constant), suppresses the reected echoes
from rain, hail and snow to clear the display. On the
X band Radar, because of its short pulselength, the
echoes from legitimate contacts can become lost in the
echoes from precipitation, called rain clutter. When
rain clutter masks the display, adjust this control to
break up the clutter and distinguish echoes. Adjust the
control so that the clutter just disappears; too much
A/C Rain action may shrink or erase the echoes from
legitimate targets.
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