Furuno Marine Radar - Manual (Page 19)

Table 1 - Comparison of X-Band and S-Band
Frequency Band Characteristics
X-Band
Short wavelength for better •
directivity
Attenuation in precipitation is
•
greater than on S-Band
Small, light-weight antennas
•
S-Band 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 reflected 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
reflected echoes away from the magnetron to prevent
both flow to the magnetron and loss of receive signal.
Scanner
The scanner transmits the radio pulses and receives
their reflected 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 reflected echoes also
pass through these slits.
Figure 4 - A typical slotted array scanner
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
figure (nf).
IF Amplifier
The IF amplifier amplifies 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
Radar FAQ’s continued ...
Q: Why does my Furuno Radar transmit for about 30 seconds, beep, and then go into stand-by mode for
5 minutes?
A: It sounds like you have the Watchman mode turned on. The Watchman mode sets the Radar to stand by
and then transmits the Radar at a user selected interval to check for target changes in the Guard Zone. If any
changes occur, the Radar will sound an audible alarm, cancel the Watchman mode and continue to transmit.
Please refer to your operator’s manual for instructions on turning this mode off.
Most Furuno Radars will have a notation of [Watchman] on the display when the function is active and the
display will beep when going into or out of this mode.
Q: Do I need to install a flux gate compass for my Radar/chart overlay and ARPA to work?
A: Yes. A stabilized heading input is required for both of these features to work.
Radar overlay will work with either an NMEA or Furuno AD10S heading input. NMEA sentences that will work
are HDG, HDM, HDT.
ARPA requires the Furuno AD10S heading input at 25 milliseconds. You can use any of Furuno’s current flux
gate compasses, an AD100 Gyro Converter, or any autopilot or flux gate compass capable of supplying this data
format. Furuno’s UHD Radars require high-speed NMEA to support ARPA, but do NOT reuire AD10S
Q: What is the difference between X-band and S-band Radars?
A: Simply put, they differ in frequency. The majority of marine Radars operate on X-band.
X-band is widely used because of the ability to utilize smaller antennas that fit on most boats and to provide
better target resolution. S-band Radars are often used for specialized applications, such as seeing through
heavy weather or precipitation and for long-range bird detection. S-band antennas are larger. The smallest
Furuno S-band antenna is 9 feet long and can be as long as 12 feet.
Q: Can I find birds using a Furuno X-Band Radar?
A: Yes, birds do reflect X-Band Radar signals well enough to be detected. You must use a high power Radar to
get a usable level of bird detection. We recommend 12kW of output power or higher to consistently detect birds
Since birds are a small target, the set-up of the Radar must be optimized and the detection range will vary.
Q: How big does my boat have to be to have a Radar?
A: There is no size restriction for a boat to have a Radar. As long as you have a stable mounting platform for the
antenna and enough dash space to mount a display, Furuno has a Radar for you.
Q: Is it okay to paint my Radar antenna?
A: Yes, it is okay to paint your Radar antenna. However, the paint MUST be epoxy-based with NO metallic
ingredients. Paint with metallic ingredients will cause poor performance and may cause damage to your Radar.
Q: My ARPA auto Radar plotter is erratic or drops targets. What could be causing this to happen?
A: All Furuno ARPA plotters require an AD10 heading input with a 25ms refresh rate. It will not work properly
with a GPS NMEA heading input. Please check to make sure you are using the proper type of heading input. The
Furuno PG500R or SC30/SC50/SC110 compass will give you the 25ms input that is required.
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