Radar

Question 1

What is the radar PRF?

Answer 1

Pulse repetition frequency - how many pulses the radar transmits per second (Hz)

Question 2

What is the frequency and wavelength of X band radar?

Answer 2

10 GHz and 3cm

Question 3

What is the frequency and wavelength of S band radar?

Answer 3

3 GHz and 10cm

Question 4

What are the advantages and disadvantages of head up display?

Answer 4

It is orientated with the ships head so gives good situational awareness. As the ships head moves though, the radar image is blurred and it only gives relative bearings rather than true bearings of targets

Question 5

What are the advantages and disadvantages of north up display?

Answer 5

The gyro screen is stabilised to North so the radar picture is fixed and stable as the vessels head changes.
The radar screen is aligned with the ECDIS display and the chart for ease of comparison and overlay.
True bearings can be taken to targets and fixed objects/land.

Question 6

What are the properties of a sea stabilised radar display?

Answer 6

When the radar is sea stabilised, the inputs are speed through the water and heading. Movement is relative to the body of water around the vessel and no account of leeway is involved.

Only speed through the water and course through the water of other targets will be shown which means the aspect is correct for collision avoidance.

Fixed objects will show a vector in relation to own vessel equal and opposite to any leeway giving a good indication of any set or drift.

Heading of all targets MUST be known for collision avoidance

Question 7

What are the properties of a ground stabilised display?

Answer 7

Inputs are speed over the ground and course over the ground.

Any own ship set/drift is applied within the COG/SOG and is subsequently applied to all targets to show their SOG and COG.

This may be deceptive if the targets are experiencing different rates of set/drift to own vessel. Vectors will be COG and so may not show the correct aspect for collision avoidance.

Display will show vessel movement relative to fixed objects which can be used during pilotage or position keeping.

Question 8

How does a SART operate?

Answer 8

X Band frequencies activate the SART which transmits 12 short pulses as dots which extend to arcs and circles as the target gets closer

Question 9

How long does a SART battery last?

Answer 9

96 hours standby and 8 hrs transmitting

Question 10

What are the 6 radar false echos?

Answer 10

1. Reflected echos - pulse bounces of an obstruction on the ship
2. Multiple echos - where the pulse bounces between the ship and the target multiple times
3. Side echos - weaker pulse either side of the main beam
4. Radar interference - from other radars
5. Second trace echos - When an echo returns after a later pulse is transmitted tricking the radar into thinking there is a closer target
6. Ghost echos (where radar pulse meets a power cable perpendicularly)

Question 11

How long should it take for a target to be processed on the radar screen?

Answer 11

1 minute to show the targets motion
3 minutes to give predicted course and speed

Question 12

What factors limit the performance of the radar?

Answer 12

1. Transmitter power
2. Antenna gain
3. Receiver sensitivity
4. Weather
5. Atmospheric conditions
6. Antenna position

Question 13

What are the requirements for range and bearing accuracy of the radar?

Answer 13

Range - 30m or 1% of the range scale in use
Bearing - Within 1 degree

Question 14

How accurate is ARPA required to be?

Answer 14

CPA within 0.3Nm
TCPA within 0.5 minutes