Radar

Question 1

Characteristics of X BAND radar

Answer 1

-3cm wavelength.
-9 Ghz
-accurate navigation.
-creates more lobes
-more clutter response.
-can detect SARTS. Range approx 8miles.

Question 2

Characteristics of S BAND radar?

Answer 2

-10cm wavelength.
-3 GHZ
-better for long range detection of targets.
-sea clutter response better (targets less likely to be hidden)

Question 3

What does a radar actually do?

Answer 3

Measures the time taken for a radio pulse to travel from a transmitter and return after being reflected by an object (target)

Question 4

Name 4 radar set components.

Answer 4

-transmitter
-antenna
-receiver
-display

Question 5

What does the transmitter do?

Answer 5

Produce short pulses through and Ariel.

Question 6

What does the antenna do?

Answer 6

Radiates the pulses, rotates to scan the horizon. Speed 20rpm.
Most common scanner= slotted waveguide.

Question 7

What does the receiver do?

Answer 7

Amplifies returning echoes and produces pulses that are accepted by the display.

Question 8

What does the display do?

Answer 8

Takes the mass of information by returning echoes and presents in a form.
-real time display.
-synthetic display.

Question 9

Name some dangers of using radar equipment.

Answer 9

-do not stand too close to radar scanner during transmissions.
-never work inside transceiver/display unit when on.
-be careful of safe distances of radar equipment for Magnetic compass.

COSWP -has safety procedure.

Question 10

Radar beam characteristics?

Answer 10

-Horizontal beam
0.5-2.0 degree width.

-vertical beam width
20-30 degree

IMO SPEC

Question 11

What does the scanner rotate at and what speed?

Answer 11

Scanner rotates 360 at 20-30 rpm.

Question 12

Why is the beam width so big?

Answer 12

Allows for movement of vessel- ie rolling and pitching etc.

Question 13

Which has good discrimination and bad discrimination?

Answer 13

Narrow horizontal beam width= good (ie can see two targets)
Wide horizontal beam width= poor ie-can see only one target

Question 14

What is bearing discrimination?

Answer 14

Ability of radar to differentiate between 2 targets on different bearings at same range.

Question 15

What are radar bearings inaccurate?

Answer 15

Due to horizontal beam width.

Question 16

What does a longer pulse give?

Answer 16

More energy transmitted, better chance of detecting a target.
Poor discrimination.

Question 17

What does a short pulse give?

Answer 17

Should be used when detecting targets close to the vessel.
Good discrimination.

Question 18

Name some factors that determine practical detection range of radar.

Answer 18

-height of scanner
-height of reflective properties of target
-atmospheric conditions.

Question 19

Name the 5 factors that affect the reflective properties of targets.

Answer 19

MASTS
Material- good radar reflectors ?

Aspect- the direction of result reflections

Size- the more pulses that strike the target the greater the response. Height good.

Texture-surface roughness (rough will scatter reflections in all directions)

Shape- affects size, aspect and surface roughness that appears to radar pulse.

Question 20

What is a propagation anomalie?

Answer 20

When the radar beam curves away from warm dry air towards cold wet air. Leads to 3 things
1- subrefraction
2-superrefraction
3-ducting

Question 21

What’s subrefraction?

Answer 21

Cold polar air over warm sea deflect beam upwards. 40% loss range reduction.

Question 22

What’s super refraction?

Answer 22

Increase of radar range when warm air is over cold air.

Question 23

What is Ducting?

Answer 23

Temperature inversion.
Can increase radar range to 400nm if antenna is in duct

Question 24

What is Minimum range and what is it affected by?

Answer 24

The ability to detect and display echoes in close proximity to the radar.

Pulse length
Vertical beam width and height of aerial.

Question 25

In true motion (ONLY) you have sea stabilisation and ground stabilisation.
Explain sea stab:

Answer 25

On radar-
Target stopped = stationary on display
Moving target= moves, water track
Land= moves contrary to tide.

Question 26

Explain ground stabilisation.

Answer 26

On radar
Target stopped= moves with tide
Moving= ground track
Land= stationary on display