Enav222 prelim lecture

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ENAV222 PRELIM LECTURE

By 3/Officer MOISES T. TEÑOSA

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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.

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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.

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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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RADAR COMPONENTS

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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.

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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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RADAR SYSTEM

CONSTANTS

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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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4.1 - THE RADAR WAVE

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Short wavelength

Long wavelength

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Pulse Length

2 usec

1 usec

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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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Types of Refraction

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Types of Refraction

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Sub-Refraction

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Ducting

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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.

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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.

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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.

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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

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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.

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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.

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00045

180

90

125

270

225

315

90

000

0

45

180

90

125

270

225

315

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180

125

270

225

315Unstabilized Head-up Stabilized North-up

90Fig. 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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RADAR CONTROLS

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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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ONINSKI

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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

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11.07

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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

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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.

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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”.

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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.

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Too little gain Normal gain Excessive gain

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Too little brilliance

Normal brilliance Excessivebrilliance

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Performance monitor working properly

Performance monitorimproperly working

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Clutter caused by rain

(no anti-rain clutter)

Break up of rain clutter by means of anti-rain clutter control

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FTC not in use FTC in use

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STC setting too low

Correct STC setting

STC setting too high

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Thank you..

3/OFFICER MOISES T.

TEÑOSA

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Enav222 prelim lecture

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