CMRT Installation & Maintenance Procedures 4 — Questions and Answers
Question 1: A radar system shows a 'transmitter fault' alarm after maintenance. After confirming all connectors are secure, the technician should next check:
- The display's brightness control
- The magnetron heater voltage and anode current readings (Correct answer)
- The antenna sweep rate
- The ARPA database memory
Correct answer: The magnetron heater voltage and anode current readings
Transmitter faults are most commonly traced to the magnetron; measuring heater voltage and anode current identifies filament failure or cathode emission degradation.
Question 2: When installing multiple radar systems on a single vessel, what technique is used to prevent mutual interference between the two radars?
- Operating both radars on identical PRFs
- Staggering PRFs or using inter-pulse synchronization (Correct answer)
- Reducing antenna rotation of one radar
- Disabling STC on the secondary radar
Correct answer: Staggering PRFs or using inter-pulse synchronization
Staggering or synchronizing PRFs between two onboard radars prevents their pulses from repeatedly coinciding and creating persistent interference arcs on each other's displays.
Question 3: During routine maintenance, a technician finds moisture inside the radar display housing. The correct immediate action is to:
- Power on the radar to dry the internal components
- Power off, remove moisture, identify the ingress point, and reseal before restarting (Correct answer)
- Apply silicone spray to the PCBs while powered
- Replace the display magnetron
Correct answer: Power off, remove moisture, identify the ingress point, and reseal before restarting
Moisture inside electronics requires power-down, drying, sealing, and inspection before restart to prevent short circuits, corrosion, or PCB damage.
Question 4: The radar performance monitor (echo box) is used post-installation to:
- Adjust heading line alignment
- Provide a repeatable reference for overall system sensitivity and transmitter power (Correct answer)
- Calibrate the ARPA tracking algorithm
- Set the range ring accuracy
Correct answer: Provide a repeatable reference for overall system sensitivity and transmitter power
The performance monitor (echo box) gives a plume length reading that serves as a repeatable baseline for comparing current system performance against the original installation standard.
Question 5: When installing radar on a sailing vessel, antenna placement must account for the mast and rigging. The key concern is:
- RF emission color coding
- Radar shadow sectors created by the mast and rigging blocking the beam (Correct answer)
- Rotary joint bearing pre-load
- Magnetron cooling air circulation
Correct answer: Radar shadow sectors created by the mast and rigging blocking the beam
Masts and rigging intercept the radar beam and create blind sectors in the display; the antenna should be positioned to minimize these shadow sectors in critical directions.
Question 6: A radar system's automatic frequency control (AFC) is misaligned after a magnetron replacement. The symptom on the display will be:
- Excessive sea clutter
- Weak or absent returns due to the receiver being off-tuned from the transmit frequency (Correct answer)
- Heading marker rotation error
- PRF instability causing range jitter
Correct answer: Weak or absent returns due to the receiver being off-tuned from the transmit frequency
AFC locks the local oscillator to track the magnetron frequency; misalignment leaves the receiver off-tuned, dramatically reducing sensitivity and target returns.
Question 7: Which standard specifies the performance requirements that marine radar equipment must meet for SOLAS vessel carriage compliance?
- IEC 62388 (Correct answer)
- IEEE 802.11ax
- ITU-R M.1175
- MIL-STD-461
Correct answer: IEC 62388
IEC 62388 is the international standard specifying minimum performance requirements for shipborne radar used on SOLAS-compliant vessels.
CMRT Installation & Maintenance Procedures 4
A radar system shows a 'transmitter fault' alarm after maintenance.
After confirming all connectors are secure, the technician should next check: