CMRT Installation & Maintenance Procedures 2 — Questions and Answers
Question 1: When installing a marine radar antenna on a mast, what is the minimum safe clearance recommended between the radar beam and the highest point where crew members may stand?
- 1 meter
- 3 meters (Correct answer)
- 5 meters
- 10 meters
Correct answer: 3 meters
A minimum 3-meter clearance between the rotating radar beam and any occupied crew area is standard safety practice to limit RF exposure.
Question 2: During radar installation, coaxial cable runs should be secured at intervals no greater than:
- 60 cm (24 inches)
- 120 cm (48 inches) (Correct answer)
- 200 cm (79 inches)
- 300 cm (118 inches)
Correct answer: 120 cm (48 inches)
Coaxial cables should be supported at maximum 120 cm intervals to prevent excessive bending stress and signal degradation from cable movement.
Question 3: What is the primary reason for installing ferrite chokes on radar power supply leads near the transceiver unit?
- Increase output power
- Suppress conducted RF interference (Correct answer)
- Improve antenna VSWR
- Reduce cable weight
Correct answer: Suppress conducted RF interference
Ferrite chokes suppress high-frequency conducted emissions that can travel along power leads and interfere with other electronic equipment.
Question 4: When aligning a radar scanner after installation, heading marker alignment is verified by:
- Comparing the radar heading line to a known fixed bearing (Correct answer)
- Measuring antenna rotation speed with a tachometer
- Checking STC sensitivity at the display
- Adjusting the magnetron anode current
Correct answer: Comparing the radar heading line to a known fixed bearing
The heading marker is aligned by rotating the antenna until the radar heading line corresponds precisely with a charted fixed object at a known bearing.
Question 5: Radar waveguide sections on a vessel should be pressure-tested with dry nitrogen or dry air to check for:
- Magnetron leakage current
- Moisture ingress and pressure integrity (Correct answer)
- Bearing friction in the rotary joint
- Modulator pulse width accuracy
Correct answer: Moisture ingress and pressure integrity
Pressurizing waveguide with dry gas reveals leaks and verifies the system will resist moisture infiltration that degrades RF transmission.
Question 6: When replacing a radar display unit onboard, the technician should first:
- Power up the new unit and check the picture
- Isolate and lock out the radar power supply (Correct answer)
- Remove the antenna from the mast
- Adjust the magnetron filament voltage
Correct answer: Isolate and lock out the radar power supply
Lockout/tagout of the radar power supply is mandatory before replacing any below-decks unit to prevent electric shock from high-voltage circuits.
Question 7: What maintenance check should be performed on the radar antenna pedestal bearing at each scheduled service interval?
- Replace the magnetron cathode
- Inspect and lubricate bearings per manufacturer specification (Correct answer)
- Recalibrate the AFC circuit
- Clean the waveguide flange gaskets with solvent
Correct answer: Inspect and lubricate bearings per manufacturer specification
Pedestal bearings must be inspected for wear and lubricated per manufacturer intervals to ensure smooth antenna rotation and accurate scan.
CMRT Installation & Maintenance Procedures 2
When installing a marine radar antenna on a mast, what is the minimum safe clearance recommended between the radar beam and the highest point where crew members may stand?