CMRT Radar Performance Testing & Monitoring 2 — Questions and Answers
Question 1: What is a 'blind sector' on a marine radar display?
- An area of no radar coverage caused by an obstruction such as a mast or funnel (Correct answer)
- A region where automatic target tracking is disabled by the operator
- The area directly astern that cannot be detected due to ship structure
- The minimum range zone where close echoes are suppressed by STC
Correct answer: An area of no radar coverage caused by an obstruction such as a mast or funnel
A blind sector is an area of the radar sweep where coverage is blocked by a physical structure on the vessel such as a mast, funnel, or superstructure, creating a gap in radar coverage.
Question 2: During a radar performance test, what does a decrease in the signal-to-noise ratio indicate?
- Improved receiver sensitivity
- Higher antenna gain than specified
- Degraded radar performance, possibly due to a weakening magnetron or increased receiver noise (Correct answer)
- Better discrimination between closely spaced targets
Correct answer: Degraded radar performance, possibly due to a weakening magnetron or increased receiver noise
A decrease in signal-to-noise ratio indicates degraded radar performance, often caused by reduced transmitter power from a weakening magnetron or increased internal noise in the receiver chain.
Question 3: What is the purpose of a calibrated corner reflector during radar performance testing?
- To absorb radar energy and reduce unwanted interference
- To provide a known radar cross-section target for range and sensitivity testing (Correct answer)
- To simulate rain clutter for anti-clutter circuit evaluation
- To measure horizontal antenna beamwidth in the field
Correct answer: To provide a known radar cross-section target for range and sensitivity testing
A calibrated corner reflector provides a target with a precisely known radar cross-section, allowing technicians to verify range accuracy and receiver sensitivity against a consistent reference standard.
Question 4: Bearing (azimuth) resolution of a marine radar is primarily determined by which parameter?
- Transmitted pulse width
- Horizontal beamwidth of the antenna (Correct answer)
- Intermediate frequency bandwidth
- Pulse repetition frequency
Correct answer: Horizontal beamwidth of the antenna
Bearing resolution is determined by the horizontal beamwidth of the antenna; a narrower beam allows the radar to distinguish two targets at the same range that are close together in azimuth.
Question 5: How does switching to a longer range scale on a marine radar affect the transmitted pulse width?
- It has no effect; pulse width is always fixed by the operator
- The pulse width decreases to improve close-range resolution
- The pulse width increases to improve detection of distant targets (Correct answer)
- The pulse width is controlled only by a separate manual adjustment
Correct answer: The pulse width increases to improve detection of distant targets
At longer range scales, the radar automatically uses longer pulse widths to increase the energy per pulse, improving detection of distant targets at the expense of range resolution.
Question 6: What is the IMO-specified maximum range error tolerance for marine navigational radar?
- ±0.1% of maximum range or ±10 meters, whichever is greater
- ±1% of the range scale in use or 30 meters, whichever is greater (Correct answer)
- ±5% of the maximum instrumented range on all scales
- ±0.5 nautical miles on any range scale selected
Correct answer: ±1% of the range scale in use or 30 meters, whichever is greater
IMO performance standards specify that range accuracy must be within ±1% of the range scale in use or 30 meters, whichever is greater, to ensure reliable distance measurements.
Question 7: In radar performance testing, what does 'system sensitivity' refer to?
- The ability of the display to render fine target detail
- The minimum input signal level that the complete radar system can detect and display (Correct answer)
- The rate at which the antenna rotates during normal operation
- The maximum output power of the transmitter at peak load
Correct answer: The minimum input signal level that the complete radar system can detect and display
System sensitivity is the minimum signal level at the antenna that the complete radar can detect and present on the display, representing the combined performance of both the transmitter and receiver subsystems.
CMRT Radar Performance Testing & Monitoring 2
What is a 'blind sector' on a marine radar display?