Enav222 prelim lecture

1
ENAV222 PRELIM
LECTURE
By
3/Officer MOISES T. TEÑOSA

3
RADAR is an acronym for Radio Detection
And Ranging.
Radar is an electronic device that detects
distant objects by bouncing radio waves off
them and listening for those echoes.

4
There are several types of radar in use and
each type had their particular application. All
radar operate on the same principles with
modifications to suit a particular application.
The type of radar used onboard ships is called
a MARINE RADAR.

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RADAR THEORY
Radar uses the basic principles of sound
and echo. You shout towards a reflecting
object and a returning sound or echo is
heard seconds later from that particular
direction.

6
Radars designed for marine application is
pulse modulated. It measures the distance to
a target by measuring the time required for a
short powerful burst of radio frequency
energy to travel to the target and return to
its source as a reflected echo.

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Since this radar waves makes a round trip,
only half of the time determines the distance.
Distance = (Speed X Time) / 2
Directional antennas are used to transmit
these pulses and to receive the echoes.

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Radar waves travels at the speed of light at:
186,000 m/sec
300,000 km/sec
162,000 nm/sec
Microsecond (usec) is used in radar applications
usec = 1 second/1,000,000
1 nm = 6.18 usec
1 usec = 0.161829 nm

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THE MAIN COMPONENTS OF A RADAR UNIT
1. POWER SUPPLY
2. MODULATOR
3. TRANSMITTER
4. ANTENNA OR SCANNER ASSEMBLY
5. RECEIVER
6. SCOPE / PLAN POSITION INDICATOR

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MAIN COMPONENTS OF A RADAR
1 - POWER SUPPLY
The power supply gets its power from the
ships main electrical supply then converts it
to the required AC/DC voltage necessary to
power the various components of the radar.

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2 - MODULATOR
Modulator insures that all circuits connected
with the radar system operate in a definite
time relationship with each other and that the
time interval between pulses is of proper
length. The modulator simultaneously sends a
synchronizing signal to trigger the transmitter
and the indicator sweep.

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3 - TRANSMITTER
This radar component is the source of radio
frequency signal or energy. It gives off a
strong short burst of energy known as pulse.
To allow the transmitter to rest and to control
the pulse length, pulse repetition rate (PRR)
and synchronization, a switching devise
called pulse modulation generator or
modulator is employed.

14
4 - ANTENNA system OR SCANNER
ASSEMBLY – takes the radio frequency energy
from the transmitter, radiates it in a highly
directional beam, receives any returning echoes,
and passes these echoes to the receiver.

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4 - ANTENNA OR SCANNER ASSEMBLY
DRIVE MOTOR – this is found on the scanner
housing and provides a 360 degrees scan
motion of the scanner reflector at the rate of
12 - 30 RPM (refer to the manufacturer'
operating manual for exact RPM).

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4.2- FLASHER SWITCH – this provides the
orientation of the ship's heading. It flashes at
the scope whenever the antenna is facing
dead ahead.
4.3- TYPES OF ANTENNA
1. parabolic (older models)
2. slotted wave guide (new models)

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4.6 - TYPES OF ANTENNA
parabolic
slotted wave guide
parabolic
slotted wave guide

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4.7 - DUPLEXER OR TRANSMIT/RECEIVE CELL
This enables the use of the scanner assembly
for both transmitting and receiving by
connecting the transmitter to the scanner
assembly during the period of transmission
while disconnecting the receiver.

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4.7 - DUPLEXER OR TRANSMIT/RECEIVE CELL
Upon completion of the transmission, the
scanner is automatically connected to the
receiver. In some models a Transmit/Receive
(TR) tube is used to block the pulses from
entering the receiver. An Anti-Transmit/Receive
(ATR) cell is used to block the echoes from
entering the transmitter.

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5 - RECEIVER
Amplifies the weak echoes but retaining its
electronic shape (Radio Frequency/RF).
5.1 - MIXER AND LOCAL OSCILLATOR STAGE
This is where the incoming echoes (in the
same form of FREQUENCY) are mixed and
aligned with the output of a local oscillator
(KLYSTRON) producing an intermediate
frequency (IF).

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5 - RECEIVER
5.1 - MIXER AND LOCAL OSCILLATOR STAGE
Tuning is accomplished when the local
oscillator is made to produce the IF and is
aligned over the incoming RF signal.

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5 - RECEIVER
5.2 - INTERMEDIATE FREQUENCY STAGE
This is composed of six (6) stages, whose
amplification is controlled by the following:
1. Gain Control
2. STC – slow time control (anti-sea clutter
control)
3. FTC – fast time control (anti-rain/snow
control)

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6 - INDICATOR
The primary function of the indicator is to provide a
visual display of the ranges and bearings of radar
targets from which echoes are received. Or it
produces a visual indication of the echo pulses in a
manner that furnishes the desired information.

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A trace or sweep rotates about the screen
in synchronization with the scanner. Contacts
or targets appear as bright spots or blips/pips
about the screen.
The screen, which is coated with
phosphorescent material, lights up with
persistence until the next rotation of the
sweep passes over again to repaint the
blips/pips.
A trace or sweep rotates about the screen in
synchronization with the scanner. Contacts or
targets appear as bright spots or blips/pips
about the screen.

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This part is also commonly called as:
1. Cathode Ray Tube (CRT)
2. The Scope
3. Plan Position Indicator (PPI)

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MODULATOR
POWER SUPPLY
WAVEGUIDE
SCANNER TARGET
PPI
TRANSMITTER
DUPLEXER
RECEIVER

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MODULATOR
POWER SUPPLY
WAVEGUIDE
SCANNER TARGET
PPI
TRANSMITTER
TR
RECEIVER
A-TR

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PULSE LENGTH
Radars can operate both at short and long
pulse. Pulse length in some radars are shifted
automatically when selecting the shorter or
longer range scales.

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Range Resolution is a measure of the
capability of a radar set to detect the
separation between targets on the same
bearing but having small differences in range.

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If the leading edge of the pulse strikes a
slightly farther target, while the trailing edge
is still striking the closer target, the reflected
echoes of the targets will appear as one
elongated target.

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POWER RELATION
The useful power of the transmitter is that
contained in the radiated pulses and is called
the PEAK POWER of the system. Power is
normally measured as an average value over
a relatively long period of time.

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CHARACTERISTICS OF
RADAR PROPAGATION

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THE RADAR WAVE
The radar radio frequency energy (radar
wave) is emitted in pulses. These radar
energy travels at the speed of light and is
subject to atmospheric refraction or bending.
It has energy, frequency, amplitude,
wavelength and rate of travel.

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THE RADAR WAVE
Each pulse of energy transmitted during a few
tenths of a microsecond or few microseconds
contains hundreds of complete oscillations.
A CYCLE is one complete oscillation or
complete wave.

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THE RADAR WAVE
FREQUENCY is the number of cycles
completed per second.
HERTZ (Hz) is the unit for frequency as:
1 Hertz (Hz) = 1 cycle/second
1 kilohertz (kHz) = 1,000 cycles/second
1 megahertz (MHz) = 1 million cycles/second

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THE RADAR WAVE
WAVELENGTH is the distance along the
direction of propagation between successive
crests or troughs. When one cycle has been
completed, the wave has traveled one
wavelength.
AMPLITUDE is the maximum displacement of
the wave from its mean or zero value.

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THE RADAR WAVE
Marine radars operates at a wavelengths of
3 centimeters ( X band), 10 centimeters
(S band). Wavelength is the length of one
cycle.

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Short wavelength
Long wavelength

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Short powerful burst during transmission
Echoes has the same characteristics but
weaker
Pulse Repetition Rate
1 pulse 1 pulse1 pulse
1 usec

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REFRACTION
If radar waves travel in straight lines or rays;
the distance to the horizon would be
dependent only on the height of the antenna.
Without the effects of refraction, the distance
to the radar horizon would be the same as
that of the geometrical horizon for the
antenna height.

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REFRACTION
Radar waves are subject to bending or
refraction in the atmosphere resulting from
travel through regions of different density.
Under standard atmosphere, distance to radar
horizon is found by the formula:
d = 1.22√ h
h=antenna height in feet
d=distance to radar horizon in nautical miles

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REFRACTION
Radar waves are bent or refracted slightly
downwards following the curvature of the
earth.
The distance to the radar horizon does not
limit the distance from which echoes maybe
received. Echoes maybe received from targets
beyond the radar horizon if their reflecting
surface extends above it.

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REFRACTION
The Standard Atmosphere is a hypothetical
vertical distribution of atmospheric
temperature, pressure and density.
Types of refraction:
1. Super-refraction
2. Sub-refraction
3. Ducting

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REFRACTION
Super-refraction
This occurs when there is an upper layer of
warm, dry air over a surface of cold, moist
air. The effect is to increase the downward
bending of the radar waves and thus increase
the ranges at which targets maybe detected.

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REFRACTION
Sub-refraction - This occurs when there is an
upper layer of cold, moist air over a surface of
warm, dry air. The effect is to bend the radar
waves upward and thus decrease the
maximum ranges at which targets maybe
detected. It also affects the minimum ranges
and may result in failure to detect low lying
targets at shorter range.

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Ducting
This phenomena occur during extreme cases
of super-refraction. Energy radiated at angles
of 10
or less maybe trapped in a layer of the
atmosphere called the Surface Radio Duct.
Radar waves are refracted downward to the
sea surface, reflected upward, downward
again within the duct and so on.

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Ducting
Energy trapped by the duct suffers little loss,
thus targets have been detected in excess of
1,400 nm. When the antenna is above the
duct, targets lying below the duct may not be
detected.

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ATTENUATION
It is the absorption and scattering of the
energy in the radar beam as it passes through
the atmosphere and causes a decrease in
echo strength. It is greater at higher
frequencies or shorter wave lengths.

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FACTORS AFFECTING
DETECTION, DISPLAY
AND MEASUREMENT OF
RADAR TARGETS

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FACTORS AFFECTING MINIMUM RANGE
1 – Pulse length
The minimum range capability of a radar is
determined primarily by the pulse length.
2 – Sea Return
Sea return or echoes received from waves
may clutter the indicator within and beyond
the minimum range established by the pulse
length and recovery time.

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FACTORS AFFECTING RANGE RESOLUTION
Range resolution is a measure of the capability of
a radar to display as separate pips the echoes of
two targets on the same bearing and are close
together.
A high degree of range resolution requires short
pulse, low receiver gain and short range scale.

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1 – Pulse Length
Two targets on the same bearing and are close
together cannot be seen as two distinct pips on
the PPI unless they are separated by a distance
greater than one the pulse length. As a result, the
echoes from two targets will blend into a single
pip, and range can be measured only to the
nearest target.

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Targets are separated by
less than the pulse length
Targets are separated by
more than the pulse length

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2 – Receiver Gain
Range resolution can be improved by proper
adjustment of the receiver gain control. The
echoes from two separate targets on the same
bearing may appear as a single pip if the receiver
is too high.

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5.3 – FACTORS AFFECTING RANGE RESOLUTION
3 – CRT Spot Size
The range separation required for resolution is
increased because the spot size formed by the
electron beam on the screen can not be focused
into a point of light. The increase in echo image
length and width varies with the CRT size and
range scale used.

65
5.3 – FACTORS AFFECTING RANGE RESOLUTION
4 – Range Scale
The pips of two targets separated by a few
hundred meters may merge on the PPI when
longer range scale is used. The shortest range
possible should be used and proper adjustment of
the receiver gain may enable their detection as
separate targets.

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5.4 – FACTORS AFFECTING BEARING ACCURACY
Bearing measurements can be made more
accurately with narrower horizontal beam widths.
Narrow beam widths will have better definition of
the target. The effective beam width can be
reduced by lowering the receiver gain setting; it
will reduce the sensitivity, maximum detection
range but better bearing accuracy.

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1 – Target Size
Bearing measurements of small targets is more
accurate than large targets because the center of
smaller pips can be identified more accurately.
2 – Target Rate of Movement
The bearings of stationary or slow moving targets
can be measured more accurately than fast
moving targets.

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3 – Stabilization of Display
Stabilized PPI display provides higher bearing
accuracy than unstabilized displays because they
are affected by yawing of the ship.

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4 – Sweep Centering Error
If the origin of the sweep is not accurately
centered on the PPI, bearing measurements will
be in error; more error is when the pip is near the
center of the PPI. A more accurate result is by
changing the range scale to shift the pip away
from the center of the PPI.

70
5 – Parallax Error
Improper use of mechanical bearing cursor will
introduce bearing errors, the cursor should be
viewed from a position directly in front of it.
Electronic bearing cursor are not affected by
parallax and centering errors, hence, provide
accurate bearing measurements.

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6 – Heading Flash Alignment
The alignment of the heading flash with the PPI
display must be such that the radar bearing must
be almost the same as that by visual observation.

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5.5 – FACTORS AFFECTING BEARING RESOLUTION
Bearing resolution is a measure of the capability
of a radar to display as separate pips the echoes
received from two targets which are at the same
range and are close together. The principal
factors that affect the bearing resolution are the
horizontal beam width, target range and the CRT
spot size.

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2 – Target Range
Two targets at the same range must be separated
by more than one beam width to appear as
separate pips on the PPI. In as much as bearing
resolution is determined primarily by horizontal
beam width, a narrow horizontal beam width will
provide a better bearing resolution.

74
3 – CRT Spot Size
The range separation required for resolution is
increased because the spot size formed by the
electron beam on the screen can not be focused
into a point of light. The increase in echo image
length and width varies with the CRT size and
range scale used.

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RADAR OPERATION
Marine radars are classified as either Relative
Motion or True Motion radars.
True Motion radars can be operated with a
relative motion display.
Relative Motion radars are fitted with special
adapters enabling operation with a true
motion display.

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RADAR OPERATION
There are two basic types used to portray the
target’s position and motion on the PPI.
The Relative Motion display shows the motion
of a target relative to the motion of the
observing (own) ship.
The True Motion display shows the actual or
true motions of the target and the observing
(own) ship.

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RELATIVE MOTION RADAR
In a relative motion radar, own ship is
positioned at the center of the PPI, regardless
whether she is stopped or in motion
(underway). When own ship is stopped,
successive pips of the target indicate its true
direction of movement and speed.

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When own ship is underway, the successive
pips of the target indicate its relative direction
of movement and speed.
A graphical solution (radar plot) is required in
order to determine its true direction of
movement and speed.

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Radar Transfer Plotting sheet

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If own ship is underway, pips of fixed targets
such as landmasses, buoys, fixed platforms,
ships at anchor, move on the PPI at a rate
equal to the speed of own ship but in opposite
direction.

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TRUE MOTION RADAR
True motion radars displays own ship and
moving targets in their true motion. Own ship
and other moving objects move on the PPI in
accordance with their true courses and speeds.
Fixed objects such as landmasses are
stationary on the PPI, such as that the radar
operator observes own ship and other ships
moving with respect to landmasses.

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True motion display
Own ship
Target Target
Targets and own
ship moves across
the screen

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ORIENTATIONS OF RELATIVE MOTION DISPLAY
There are two basic orientations used for the
display of relative motion on the PPI.
1.Head-up (unstabilized) display. In this display,
the heading flasher is aligned with the ship’s fore
and aft line (0000
)regardless of the heading. The
pips are at their measured distances but in a
direction relative to own ship.

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This type of display is only suitable for open sea
watchkeeping as the targets appear on the PPI in
exact position as they are visually observed. It is
the targets that move every time the ship yaws and
there is difficulty of converting relative bearings to
true.

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2. North-up (stabilized) display. In this display, the
heading flasher is aligned with the ship’s fore and
aft line (0000
)regardless of the heading. A gyro
repeater attached to the unit indicates the ship’s
heading. The pips are at their measured distances
but in a true direction from own ship.

87
This display is also suitable for open sea watch
keeping as the targets appear on the PPI in exact
position as they are visually observed, however,
there is difficulty when taking bearings every time
the ship yaws as the gyro repeater keeps on
moving.

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ORIENTATIONS OF TRUE MOTION DISPLAY
3. True Motion radars are usually, stabilized North-
up although it can also be on Head-up display. The
display is similar to a navigational chart and it is the
ship’s heading flasher that changes direction. It is
best for coastal navigation and watchkeeping.
When on stabilized mode, the Cathode Ray Tube
(CRT) of True and Relative motion radars are
automatically rotated to compensate for the setting.

89
000
45
180
90
125
270
225
315
90
000
0
45
180
90125
270
225
315
45
180
125
270
225
315
Unstabilized Head-up Stabilized North-up

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Fig. 1: Own ship and targets underway
Stabilized; North-up

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Fig. 2: Own ship
altered course
Fig. 3: Movement of targets
after course alteration
Stabilized; North-up

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Fig. 4: Own ship and targets underway
Unstabilized; Head-up

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Fig. 5: Own ship
altered course
Fig. 6: Movement of targets
after course alteration
Unstabilized; Head-up

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7 – RADAR CONTORLS
Advanced electronic technology has made modern
radars more accurate, reliable and compact than
the older models and these includes their operating
controls. Due to communication, language and
designs, the radar operating controls were
internationally standardized by the use of symbols.
Modern design and technology has eliminated some
of these operating controls.

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Head - up
North - up
Heading Marker
Alignment

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Transmitted Power Monitor
Display Brilliance
Scale Illumination

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Gain
Tuning
Range Rings
Brilliance
Short
Pulse
Long
Pulse
Selector

100
11.07
12
Bearing Marker
Variable Range
Marker
Transmit/Receive Monitor
Range Selector
Range Indicator
Variable Range
Indicator

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Anti-Clutter
Rain Minimum
Anti-Clutter
Rain Maximum
Anti-Clutter
Sea Maximum
Anti-Clutter
Sea Minimum

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SETTING – UP PROCEDURE
The proper set up switch off procedure
must be observed before a radar is
operated. Observing the proper procedure
will prolong the life of the various delicate
parts and components of a radar.

105
Steps for setting up a radar.
1.Make sure that the scanner is free of all
obstruction.
2.Switch the power to “ON”; wait for 2-3 or
until the ready light is light.
3.Switch to “OPERATE”.

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4. Adjust the “BRILLIANCE” control; just
enough to see a little speckled background.
5. Set the “RANGE SCALE” medium range.
6.Set either to “SHORT or LONG PULSE”.
7.Adjust the “GAIN, and TUNING”.

107
8. Adjust the brightness of the “FIX RANGE
RINGS, VRM, PANEL.
9. Adjust the “RAIN and SEA anti-clutter” as
appropriate.
A radar should not be continuously switch
“ON” and “OFF”, instead it should be
“STANDY” mode.

108
Too little gain Normal gain Excessive gain

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Too little
brilliance
Normal brilliance Excessive
brilliance

110
Performance monitor
working properly
Performance monitor
improperly working

111
Clutter caused by rain
(no anti-rain clutter)
Break up of rain clutter
by means of anti-rain
clutter control

113
STC setting
too low
Correct STC
setting
STC setting
too high

114
Thank you..
3/OFFICER MOISES T.
TEÑOSA

Enav222 prelim lecture

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