RADAR

Question 1

When would you select a longer range? (3 factors)

Answer 1

• If you are concerned about distant weather
• You want to acquire a target further than your current range
• Wish to take a range of a distant object

Question 2

Considerations when using different ranges

Answer 2

• Shorter range will be better for navigating and will have reduced range and bearing discrimination
• Generally would have to increase pulse length when going to longer ranges which would increase range and bearing discrimination but would also let you potentially see upcoming targets/weather

Question 3

The difference between X band S band. Advantages and disadvantages of each

Answer 3

• X band (3cm, 9GHz) has better definition, range discrimination and bearing accuracy. Affected more by rain than S band.
• S band (10cm, 3GHz) has better range and less attenuation. Less sea clutter on S band therefore less probability of targets being masked

Question 4

Beam width of X band and S band

Answer 4

• X band: HBW 1 degree. VBW 23 degrees
• S band: HBW 2 degrees. VBW 30 degrees
• Can reduce HBW with a larger scanner

Question 5

How can parallel indexing help with coastal navigation?

Answer 5

• Parallel indexing is used as a measure to monitor the progress of a vessel along a track and to minimise the cross track distance. A PI line can be used in parallel with the course to be steered and be on the edge of the coast or a conspicuous feature. If you veer off your track towards the coast the PI line will move across that feature allowing you to see that the feature is now closer to you. The PI line should stay fixed on the feature if you are following your course. It is good for seeing if there is a tide setting you in a different direction. It is good for costal navigation to allow for a safety margin.

Question 6

The difference between a shadow and a blind sector?

Answer 6

• In a blind sector there is no target response
• In a shadow sector some performance is possible, especially with the longer wavelengths of S band

Question 7

How would a radar overlay help a pilot?

Answer 7

• To show equipment is functioning correctly
• Helps with easy identification of navigation marks for position fixing
• Shows where targets are in relation to the channel are where they are headed

Question 8

Sea clutter. How to get good setting and precautions. Same with rain

Answer 8

• Adjust rain first then sea
• Rain clutter reduces thickness of target so just leading edge can be seen. The effect is constant over the range in use
• Sea clutter suppresses gain. It works outwards from the centre, the more it is turned up the greater range it affects.
• Turning up either sea or rain clutter too much can remove targets from the display

Question 9

What does true vector show, same question for relative. Which vector is unrelated to own ships heading and speed

Answer 9

• True vector shows your ships heading and speed for your own vessel and other vessels
• Relative vector shows nothing for your own vessel but does show the relative course of other ships in relation to your own vessel. If another vessels relative vector is crossing through your position you are on a collision course

Question 10

Which vector is better to use if your inputs go down

Answer 10

• Relative vectors as they do not require inputs to work

Question 11

Explain: side lobe, multiple echoes, blind sector and shadow sector

Answer 11

• Side lobe is created from electromagnetic energy leaking from the side of the scanner. This creates lobes besides the main beam, these lobes can pick up targets at close range and therefore create false targets either side of the real target in the shape of a semi circle or sometimes even full circle.
• Multiple echoes generally occur when another ship is in close range, the radar pulse has enough power to bounce back and forth between your ship and there’s several times. As a result you can see additional echoes at multiples of the true echo.
• There is no radar performance in a blind sector, the beam is completely blocked. Some performance is possible in a shadow sector, especially when using S band

Question 12

How to fix a misaligned heading marker

Answer 12

• You can place a conspicuous object in line with the bow of the yacht. If the object is not dead ahead on your radar then your heading is misaligned. You can also take a relative bearing of a conspicuous object at the same time visually and on radar and compare the two, if there is a continuous discrepancy then your heading marker is likely to be misaligned

Question 13

How to set up brilliance, gain and tune

Answer 13

• Brilliance: choose a preset setting (day, dusk, night) and then adjust the brightness so OOW can see display clearly
• Gain: turn up until you get an even speckled background with all other enhancement controls set at 0.
• Tune: Adjust for best response from target near the edge of the display

Question 14

4 things to consider when using CPA alarms

Answer 14

• The state of visibility
• Traffic density
• How quickly your boat can manoeuvre
• Proximity to navigational hazards
• Masters standing orders

Question 15

Create a table to show the difference between relative motion and true motion

Answer 15

• What are inputs for each
• What are the presentations for each (maybe worded as modes)
• What motion is experienced in each
• What trails are displayed
• How is a fixed object displayed
• How are vectors displayed

Question 16

Radar components?

Answer 16

Question 17

What is is multi-path error?

Answer 17

Multi-path is when a radio wave bounces back from i.e a mountain, back to the boat but the radar is transmitting and can’t pick up the signals, the radio wave therefore bounces of the ship back to the mountain and then back to the ship again where the radar can receive. This will make your target on your display at double the distance at the same bearing as the radio wave have travelled double the distance at the same bearing.

Question 18

What is side lobe error?

Answer 18

Side lobe is created from electromagnetic energy leaking from the side of the scanner. This creates lobes besides the main beam, these lobes can pick up targets at close range and therefore create false targets either side of the real target in the shape of a semi circle or sometimes even full circle. (cock n’ balls)

Question 19

What’s subrefraction?

Answer 19

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

Question 20

What’s super refraction?

Answer 20

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

Question 21

What is ducting?

Answer 21

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

Question 22

What are the radar components?

Answer 22

Power source, Transmitter (magnetron), T/R Cell (duplexer), Antenna (Scanner) (Also a motor to drive the antenna), Receiver/Amplifier, Display/PPI (Plan position indicator)

Question 23

How do you setup a radar?

Answer 23

Big Randy Girls take cock hard
1. Brilliance (set the brightness for your display)
2. Range (go to a suitable range)
3. Gain (turn up until you get white speckles)
4. Tuning (tune the receiver to get the best display, this is normally done automatic)
5. Clutter: Rain & Sea clutter in that order.
6. Heading (check so heading marker is not off, if it is means radar could be compromised)

Question 24

What is the Minimum Range & What is it effected by?

Answer 24

Minimum range is affected by;
1. scanner height above sea level
2. vertical beam-width of the scanner
3. pulse length
4. receiver paralysis (T/R cell changeover)
5. physical obstructions

For a radar to comply with the marine radar performance specification a target must remain visible down
to a minimum range of 50 metres when the scanner is mounted 15 metres above the sea.

Question 25

State three target characteristics which may affect its detection by radar

Answer 25

a) Any three from Shape, aspect, material, size and surface texture (6)

Question 26

(b) Describe the causes of “side lobes”

Answer 26

b) Side lobes caused by “leakage” of E.M radiation from scanner outside of
main beam. (5)

Question 27

(d) Describe how an observer should obtain an accurate bearing of a spot target
displaying side lobes.

Answer 27

d) Take the bearing through he centre as side lobes are assumed to be
symmetrical about “real” target. (5)

Question 28

1. Describe the effects of Horizontal beam width of the radar pulse on the spot size
   of the displayed target and the radar bearing accuracy. (10 marks)

Answer 28

HBW increases the spot size of the target in azimuth to the beam width.
HBW should be as small as possible.
Bearing accuracy also affected by the beam width.
Expanded ½ BW either side of target.
Reduces bearing discrimination of target.

Question 29

2. State 3 main factors, which affect the minimum detection range of a radar.
   (10 marks)

Answer 29

Pulse length.
Scanner height.
Vertical beamwidth.
Ship shadow sectors.
Power output of magnetron.

Question 30

Explain why radar ranges are more accurate than bearings when used
to fix the ships’ position. (10 marks)

Answer 30

Key words:
Pulse length.
Beam width.
Range is measured by time taken for pulse to return from target measured
from start of pulse to start of return. Error only due to spot size.
Bearing is measured by azimuth of aerial. Pulse returned from moment
leading edge of beam touches target to the moment the trailing edge clears
target. Target displayed as width of beam, therefore bearing ‘guess’ of the
centre of target.

Question 31

Explain the terms Range discrimination and Bearing discrimination.
(10 marks)

Answer 31

Range Discrimination: targets separated by more than half pulse length shows as separate
targets.
Bearing Discrimination: targets separated by more than the beam width will show as
separate targets.
Discrimination is the ability of the set to show two close targets as separate
targets.

Question 32

a) State the mode of display indicated by the trails in the diagram
b) Is the display sea stabilised or ground stabilised?
c) State which targets, if any, have a cpa of less than 1.5 Nm with own
ship
d) State the approximate course and speed of target A
e) State the course and speed of target C
f) Determine the approximate set of the tide

Answer 32

a) True motion trails (2)
b) Sea stabilised (3)
c) No targets (2)
d) 315o
at half our speed, 12 knots (3)
e) 045o
at 24 kts (2)
f) 135o
+/- 15o
. (3)

Question 33

Multiple echoes (5)

Answer 33

Question 34

Side Lobes (5)

Answer 34

Question 35

Shadow Sector (5)
Blind Sector (5)

Answer 35

Question 36

List two factors to be taken into account when choosing targets suitable
for parallel indexing (4)

Answer 36

• Within working range.
• Radar conspicuous.
• Positively identified.
• Beware of using fixed floating marks that may be out of position

Question 37

Describe the effect of heavy rain on:
i) the radar detection of targets beyond the rain; and,
(2)
ii) the detectability of targets within the rain shower.
(4)

Answer 37

i) Echo strength reduced due to attenuation and scattering (2 marks)
ii) Echo strength reduced due to attenuation and scattering and
target masked by rain clutter. (4 marks)

Question 38

20 Marks
a) What type of trails are indicated on the diagram?
b) State which targets have a cpa of less than 1.5 Nm with own ship
c) State the approximate course and speed of target A
d) State the course and speed of target D
e) Determine the approximate set of the tide.

Answer 38

a) Relative trails (4)
b) Target C (only this answer is acceptable, an answer C and B for example
would receive no marks) (4)
c) 045o
at a faster speed than own ship, accept any speed within reason. (4)
d) 045o
at 24 kts (4)
e) 135o
, accept a set that causes own ship to be set away from the fixed
navigation mark. (4)

Question 39

Describe, with the aid of a diagram, the causes and effects of the
following:
Side lobes

Answer 39

Question 40

With reference to RADAR, describe, with the aid of diagrams
1 How the following errors in input will affect target information derived from a radar
plot; (8 marks)
a. Incorrect compass input. (ie -If there is Gyro error).
b. Incorrect speed input.
2. The effect of the following on Radar echoes. (12 marks)
a. Horizontal beam width on targets at the same range.
b. Pulse length on targets on the same bearing.

Answer 40

Marking scheme.
1 (a) OWA triangle showing error in heading and speed of target.
(b) Error in relative bearings of targets.
2 (a)Diagram showing two targets painted as one if closer than 1 beam width.
(b) showing 2 targets painted as one if less that ½ pulse length apart.