CMRT Power Systems & Interference Mitigation 2 — Questions and Answers
Question 1: What causes precipitation (rain) clutter on a marine radar display?
- Reflection of the radar signal from raindrops, snowflakes, or hail in the atmosphere between the antenna and the target (Correct answer)
- Electrical interference from the ship's engine room
- Moisture inside the waveguide causing signal loss
- Tropospheric ducting over long distances
Correct answer: Reflection of the radar signal from raindrops, snowflakes, or hail in the atmosphere between the antenna and the target
Precipitation clutter is caused by radar energy scattered back from water droplets in rain, snow, or hail, which can mask weaker target echoes behind or within the precipitation.
Question 2: What is the function of FTC (Fast Time Constant) or rain clutter control in a radar receiver?
- It speeds up the antenna rotation rate in heavy weather
- It differentiates the received signal, emphasizing sharp leading edges of echoes and reducing the effect of extended precipitation returns (Correct answer)
- It increases the pulse repetition frequency during rain
- It switches the radar to a higher frequency band
Correct answer: It differentiates the received signal, emphasizing sharp leading edges of echoes and reducing the effect of extended precipitation returns
FTC applies differentiation to the received video signal, highlighting the leading edges of targets while suppressing the more gradual, sustained returns from rain clutter.
Question 3: What type of interference on a radar display typically appears as a series of dots or dashes in a spiral or rotating pattern?
- Sea clutter
- Radar-to-radar interference from another vessel's radar operating on a similar frequency (Correct answer)
- Second-trace echoes from atmospheric ducting
- Magnetron sparking artifacts
Correct answer: Radar-to-radar interference from another vessel's radar operating on a similar frequency
Radar-to-radar interference from another ship's radar produces characteristic spiral, dotted, or dashed patterns that slowly rotate or change with each antenna sweep.
Question 4: What is the purpose of an interference rejection (IR) control on a marine radar?
- To prevent the radar from interfering with the ship's VHF radio
- To detect and suppress pulse interference from other nearby radars by comparing consecutive sweeps and rejecting non-repeating returns (Correct answer)
- To limit transmitted power near port areas
- To align the radar with the vessel's magnetic compass
Correct answer: To detect and suppress pulse interference from other nearby radars by comparing consecutive sweeps and rejecting non-repeating returns
Interference rejection compares successive antenna sweeps and suppresses returns that appear only once (as other radars' pulses would), while preserving genuine echoes that appear consistently.
Question 5: How does ice or heavy salt spray accumulation on a radar radome affect performance?
- It has no effect because radomes are designed to be impermeable
- It can attenuate the transmitted and received signal, reducing maximum range and target detectability (Correct answer)
- It increases the antenna gain by focusing the beam
- It shifts the radar frequency to a lower band
Correct answer: It can attenuate the transmitted and received signal, reducing maximum range and target detectability
Ice, snow, or heavy salt deposits on a radome introduce additional RF attenuation, reducing the energy reaching and returning from targets and degrading overall radar performance.
Question 6: What is the purpose of impedance matching in a radar RF transmission line (waveguide or coaxial cable)?
- To maximize power transfer and minimize reflections (VSWR) between the transmitter, transmission line, and antenna (Correct answer)
- To set the radar's operating frequency
- To prevent lightning from damaging the magnetron
- To synchronize the antenna scan with GPS timing
Correct answer: To maximize power transfer and minimize reflections (VSWR) between the transmitter, transmission line, and antenna
Proper impedance matching ensures maximum RF power is transferred from transmitter to antenna with minimal reflected power, which if unmatched could damage the transmitter or reduce range.
CMRT Power Systems & Interference Mitigation 2
What causes precipitation (rain) clutter on a marine radar display?