Radar

Question 1

Pulse length

Answer 1

Pulse length is determined by the design of the modulator circuit. A radar normally has more than one pulse duration, switched automatically as the displayed range is increased or decreased. When very short ranges are selected on the display the transmitted pulse length is made very short, typically 0.07μ seconds. Conversely, when long range is selected a long pulse duration is employed, typically lμ second. Some radars use three switched pulse durations, short, medium and long in accordance with the range selected on the display.

Question 2

Carrier Frequency

Answer 2

Carrier frequency is the radio frequency on which the transmission is made. Marine radar equipment is manufactured to operate in either one of two frequency bands.
‘X’ Band (3 cm) 9 GHz
‘S’ Band (10 cm) 3 GHz

Question 3

‘S’ Band (10 cm) 3 GHz

Question 4

Sea Clutter

Answer 4

A/C Sea (STC): Sea control, also called STC (Sensitivity Time Constant), suppresses reflections from waves near own ship. It reduces the sensitivity of the receiver from the centre out.
The proper setting should be such that the clutter is suppressed. and echoes become distinguishable. If the control is set too high, both sea clutter and echoes will disappear from the display. When there is no sea clutter visible on the display, turn the control fully counter clockwise.

Question 5

Precipitation Clutter

Answer 5

The rain control suppresses the reflected echoes from rain, hail and snow to clear the display. Via video processing it does not display the leading-edge returns.
On the X-band radar, because of its short pulse length, the echoes from legitimate contacts can become lost in the echoes from precipitation, called rain clutter. When rain clutter masks the display, adjust this control to break up the clutter and distinguish echoes. Adjust the control so that the clutter just disappears; too much A/C rain action may shrink or erase the echoes from legitimate targets.

Question 6

Detection Characteristics of Radar Targets

Answer 6

The ability of the radar set to produce a paint on the screen which represents a target depends largely upon the amount of energy that the target is able to reflect back to the scanner.
MASTS

Question 7

Setting up a Radar

Answer 7

BIG RANDY GIRLS TAKE COCK
Brilliance
Range
Gain
Tune
Clutter

Question 8

Pre departure radar checks

Answer 8

The performance of the radar should be checked using the Performance Monitor before sailing and at least every four hours whilst a radar watch is being maintained. VRM Checks against range rings, ERBL cross check against compass.

Question 9

Good Radar Practice

Answer 9

• The quality of the performance of the radar needs to be checked regularly: A
performance monitor if fitted should be used for this purpose.
• Misalignment of the heading marker, even if only slightly, can lead to
dangerously misleading interpretation of potential collision situations.
• Small vessels, ice and other floating objects such as containers may not be
detected by the radar.
• Video processing techniques should be used with care.
• Echoes may be obscured by sea or rain clutter.
• Masts or other structural features may cause shadow or blind sectors on the
display.

Question 10

Performance Monitor

Answer 10

The performance monitor provides a check of the performance of the transmitter.
Being limited to a check of the operation of the equipment, the performance monitor
does not provide any indication of performance as it might be affected by the
propagation of the radar waves through the atmosphere. Thus, a good check on the
performance monitor does not necessarily indicate that targets will be detected. When
the performance monitor is used, a plume extends from the centre of the PPI.

The length of the plume, which is dependent upon the strength of the echo received
from the echo box in the vicinity of the antenna, is an indication of the performance of
the transmitter and the receiver. The length of this plume is compared with its length
when the radar is known to be operating at high performance
.

Question 11

Radar Displays

Answer 11

Radar Displays
• Un-stabilised means no compass input. Relative bearings.
• Stabilised means gyro fed in.
• H-up un-stabilized by any external heading input, uses that it was installed
forward facing. Alterations of heading are shown by the entire image rotating
away from the turn. Bearing will be relative to ships head.
• C-up display is stabilised by an external heading input, small alterations of
headings are shown by the heading marker swinging side to side. Bearing can
be taken relative or bearings.
• N-up image is stabilised, and it aligns with a chart or chart plotter. This is the
standard setting.
• True motion and relative motion - True motion moves across the screen.
• Sea and ground stabilised. Log input.
• Sea stabilised effects of tide and wind on your vessel is accounted for any free
floating or stationary object or moving targets will be shown with their true heading calculated via ARPA. For collision avoidance, it must be sea stabilised.
• Moving vessels have their course and speed calculated by ARPA.
• Stationary free-floating objects appear stopped.
• Anchored vessels navigation marks appear to move in the opposite direction of
the combined effect of tide and current.
• Ground stabilised GPS feed in or doppler operating in BT ARPA could be
wrong as it uses your course and speed to give out course and speed of other vessels. Can be used for pilotage or navigation but not collision avoidance.

Question 12

Sea and ground stabilised., Log input