CMRT Troubleshooting & Repair Techniques 2 — Questions and Answers
Question 1: A marine radar displays a 'heading line' that drifts slowly over time. What is the most likely cause?
- Faulty magnetron
- Gyrocompass or heading sensor drift (Correct answer)
- Defective RF circulator
- Corrupted chart overlay
Correct answer: Gyrocompass or heading sensor drift
Heading line drift is caused by drift in the gyrocompass or heading sensor feeding data to the radar.
Question 2: When testing a radar's TR (transmit/receive) limiter, a technician finds it has high insertion loss in the receive path. What symptom will this cause?
- Increased transmitter power output
- Reduced receiver sensitivity and poor target detection (Correct answer)
- False echoes on the display
- Bearing discrimination errors
Correct answer: Reduced receiver sensitivity and poor target detection
High insertion loss in the TR limiter attenuates the received signal, reducing receiver sensitivity and degrading target detection.
Question 3: A radar technician measures abnormally high anode current on the magnetron. What should be checked first?
- Antenna rotational speed
- Modulator pulse width and peak voltage (Correct answer)
- Video amplifier gain
- Gyrocompass interface
Correct answer: Modulator pulse width and peak voltage
High anode current is typically caused by incorrect modulator pulse width or excessive peak voltage applied to the magnetron.
Question 4: A radar system exhibits 'ringing' artifacts — bright concentric rings near the center of the display. What is the most probable cause?
- Excessive receiver gain
- Poor transmitter-to-antenna impedance match causing reflections (Correct answer)
- Defective video processor
- Compass input failure
Correct answer: Poor transmitter-to-antenna impedance match causing reflections
Ringing artifacts are caused by impedance mismatches in the waveguide or antenna, creating internal reflections that appear as concentric rings.
Question 5: After replacing a radar display unit, the technician notices the range rings are no longer accurate. What is the most likely calibration step needed?
- Re-tune the magnetron frequency
- Calibrate the timebase (sweep) generator (Correct answer)
- Adjust the antenna rotation speed
- Re-initialize the GPS interface
Correct answer: Calibrate the timebase (sweep) generator
Range ring accuracy depends on the timebase generator; calibrating it ensures range rings correctly represent true distances.
Question 6: A technician notices the radar antenna makes a grinding noise during rotation. After inspection, what is the FIRST component to check?
- Waveguide rotary joint
- Antenna drive motor brushes
- Pedestal bearing assembly (Correct answer)
- Slotted waveguide array
Correct answer: Pedestal bearing assembly
Grinding noise during rotation most commonly indicates worn or damaged pedestal bearings requiring inspection and replacement.
Question 7: A X-band marine radar's STC (Sensitivity Time Control) circuit is suspected to be faulty. What symptom would confirm this?
- Loss of distant targets beyond 12 NM
- Persistent sea clutter at short ranges obscuring nearby targets (Correct answer)
- Incorrect bearing readout
- Display flickering at low brightness settings
Correct answer: Persistent sea clutter at short ranges obscuring nearby targets
A faulty STC circuit fails to suppress near-range receiver gain, allowing sea clutter to overwhelm nearby targets.
CMRT Troubleshooting & Repair Techniques 2
A marine radar displays a 'heading line' that drifts slowly over time.
What is the most likely cause?