Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
RADAR/ARPA – RADAR AND AUTOMATIC RADAR PLOTTING AID | EXAM
QUESTIONS AND CORRECT ANSWERS | VERIFIED MARITIME
NAVIGATION COMPLETE EXAM 2026/2027
RADAR AND AUTOMATIC RADAR PLOTTING AID (RADAR/ARPA)
1. A marine radar determines the range of a target by measuring:
A. The strength of the returned echo
B. The phase difference between two receiving antennas
C. The time interval between transmission of a pulse and reception of its
echo
D. The frequency shift of the returned signal
C. The time interval between transmission of a pulse and reception
of its echo
Radio energy travels at a known constant speed, so half the round-trip
time gives the target's range.
2. Approximately how long does it take a radar pulse to travel to a
target 1 nautical mile away and return?
A. 1.85 microseconds
B. 24.72 microseconds
C. 12.36 microseconds
D. 6.18 microseconds
C. 12.36 microseconds
At about 300 m per microsecond, the 3,704 m round trip for one nautical
mile takes roughly 12.36 µs.
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, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
3. An X-band marine radar operates at a frequency of approximately:
A. 3 GHz
B. 9 GHz
C. 1.5 GHz
D. 15 GHz
B. 9 GHz
X-band marine radars transmit in the 9.2–9.5 GHz band, giving a
wavelength of about 3 cm.
4. The wavelength of an S-band marine radar is approximately:
A. 30 cm
B. 3 cm
C. 1 cm
D. 10 cm
D. 10 cm
S-band radars operate near 3 GHz, which corresponds to a wavelength of
about 10 cm.
5. Compared with an X-band radar, an S-band radar is:
A. Able to use a smaller antenna for the same beamwidth
B. Less affected by sea and rain clutter
C. Better at detecting small targets at very short range
D. Better at bearing discrimination for the same antenna length
B. Less affected by sea and rain clutter
The longer S-band wavelength is scattered and attenuated less by rain
and waves, so clutter is reduced.
6. Which component generates the high-power microwave pulses in a
conventional marine radar?
A. The local oscillator
B. The TR cell
C. The crystal mixer
D. The magnetron
D. The magnetron
The magnetron converts the high-voltage pulses from the modulator into
short bursts of microwave energy.
Page 2 of 63
, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
7. The main function of the TR (transmit/receive) cell is to:
A. Protect the receiver from the transmitter's high-power pulse
B. Generate the timing trigger for the display
C. Keep the antenna in step with the display sweep
D. Amplify weak echoes before they reach the mixer
A. Protect the receiver from the transmitter's high-power pulse
During transmission the TR cell fires and blocks the path to the sensitive
receiver, then recovers to pass the echoes.
8. The modulator in a radar transmitter is responsible for:
A. Converting received echoes to an intermediate frequency
B. Controlling the antenna rotation speed
C. Removing sea clutter from the displayed picture
D. Supplying high-voltage pulses of the correct length and timing to the
magnetron
D. Supplying high-voltage pulses of the correct length and timing to
the magnetron
The modulator stores energy and releases it as a sharp pulse that drives
the magnetron for the selected pulse length.
9. The trigger (timing) unit of a radar ensures that:
A. The antenna always points at the strongest echo
B. The receiver gain varies with the sea state
C. The magnetron frequency stays constant
D. Transmission and the start of the display timebase occur at the same
instant
D. Transmission and the start of the display timebase occur at the
same instant
Range can only be measured correctly if the display timing begins exactly
when each pulse leaves the antenna.
Page 3 of 63
, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
10. In a superheterodyne radar receiver, the mixer combines the
incoming echo with the local oscillator signal to produce:
A. An audio tone for the operator
B. A video signal that goes straight to the display
C. A higher microwave frequency for amplification
D. An intermediate frequency signal, typically around 60 MHz
D. An intermediate frequency signal, typically around 60 MHz
Converting to a lower intermediate frequency allows stable, high-gain
amplification before detection.
11. Waveguide is normally used instead of coaxial cable in X-band
radar installations because it:
A. Amplifies the signal on its way to the antenna
B. Carries microwave energy with much lower losses
C. Can carry DC power to the scanner motor
D. Is cheaper and more flexible to install
B. Carries microwave energy with much lower losses
At microwave frequencies coaxial cable losses are high, whereas a hollow
waveguide transmits the energy efficiently.
12. Which statement about pulse length is correct?
A. A shorter pulse increases detection range and improves minimum
range
B. A longer pulse increases detection range but degrades range
discrimination
C. Pulse length has no effect on range discrimination
D. A longer pulse improves both detection range and range discrimination
B. A longer pulse increases detection range but degrades range
discrimination
A longer pulse carries more energy for distant targets, but it smears close
targets on the same bearing together.
Page 4 of 63
RADAR/ARPA – RADAR AND AUTOMATIC RADAR PLOTTING AID | EXAM
QUESTIONS AND CORRECT ANSWERS | VERIFIED MARITIME
NAVIGATION COMPLETE EXAM 2026/2027
RADAR AND AUTOMATIC RADAR PLOTTING AID (RADAR/ARPA)
1. A marine radar determines the range of a target by measuring:
A. The strength of the returned echo
B. The phase difference between two receiving antennas
C. The time interval between transmission of a pulse and reception of its
echo
D. The frequency shift of the returned signal
C. The time interval between transmission of a pulse and reception
of its echo
Radio energy travels at a known constant speed, so half the round-trip
time gives the target's range.
2. Approximately how long does it take a radar pulse to travel to a
target 1 nautical mile away and return?
A. 1.85 microseconds
B. 24.72 microseconds
C. 12.36 microseconds
D. 6.18 microseconds
C. 12.36 microseconds
At about 300 m per microsecond, the 3,704 m round trip for one nautical
mile takes roughly 12.36 µs.
Page 1 of 63
, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
3. An X-band marine radar operates at a frequency of approximately:
A. 3 GHz
B. 9 GHz
C. 1.5 GHz
D. 15 GHz
B. 9 GHz
X-band marine radars transmit in the 9.2–9.5 GHz band, giving a
wavelength of about 3 cm.
4. The wavelength of an S-band marine radar is approximately:
A. 30 cm
B. 3 cm
C. 1 cm
D. 10 cm
D. 10 cm
S-band radars operate near 3 GHz, which corresponds to a wavelength of
about 10 cm.
5. Compared with an X-band radar, an S-band radar is:
A. Able to use a smaller antenna for the same beamwidth
B. Less affected by sea and rain clutter
C. Better at detecting small targets at very short range
D. Better at bearing discrimination for the same antenna length
B. Less affected by sea and rain clutter
The longer S-band wavelength is scattered and attenuated less by rain
and waves, so clutter is reduced.
6. Which component generates the high-power microwave pulses in a
conventional marine radar?
A. The local oscillator
B. The TR cell
C. The crystal mixer
D. The magnetron
D. The magnetron
The magnetron converts the high-voltage pulses from the modulator into
short bursts of microwave energy.
Page 2 of 63
, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
7. The main function of the TR (transmit/receive) cell is to:
A. Protect the receiver from the transmitter's high-power pulse
B. Generate the timing trigger for the display
C. Keep the antenna in step with the display sweep
D. Amplify weak echoes before they reach the mixer
A. Protect the receiver from the transmitter's high-power pulse
During transmission the TR cell fires and blocks the path to the sensitive
receiver, then recovers to pass the echoes.
8. The modulator in a radar transmitter is responsible for:
A. Converting received echoes to an intermediate frequency
B. Controlling the antenna rotation speed
C. Removing sea clutter from the displayed picture
D. Supplying high-voltage pulses of the correct length and timing to the
magnetron
D. Supplying high-voltage pulses of the correct length and timing to
the magnetron
The modulator stores energy and releases it as a sharp pulse that drives
the magnetron for the selected pulse length.
9. The trigger (timing) unit of a radar ensures that:
A. The antenna always points at the strongest echo
B. The receiver gain varies with the sea state
C. The magnetron frequency stays constant
D. Transmission and the start of the display timebase occur at the same
instant
D. Transmission and the start of the display timebase occur at the
same instant
Range can only be measured correctly if the display timing begins exactly
when each pulse leaves the antenna.
Page 3 of 63
, Radar and Automatic Radar Plotting Aid (RADAR/ARPA)
10. In a superheterodyne radar receiver, the mixer combines the
incoming echo with the local oscillator signal to produce:
A. An audio tone for the operator
B. A video signal that goes straight to the display
C. A higher microwave frequency for amplification
D. An intermediate frequency signal, typically around 60 MHz
D. An intermediate frequency signal, typically around 60 MHz
Converting to a lower intermediate frequency allows stable, high-gain
amplification before detection.
11. Waveguide is normally used instead of coaxial cable in X-band
radar installations because it:
A. Amplifies the signal on its way to the antenna
B. Carries microwave energy with much lower losses
C. Can carry DC power to the scanner motor
D. Is cheaper and more flexible to install
B. Carries microwave energy with much lower losses
At microwave frequencies coaxial cable losses are high, whereas a hollow
waveguide transmits the energy efficiently.
12. Which statement about pulse length is correct?
A. A shorter pulse increases detection range and improves minimum
range
B. A longer pulse increases detection range but degrades range
discrimination
C. Pulse length has no effect on range discrimination
D. A longer pulse improves both detection range and range discrimination
B. A longer pulse increases detection range but degrades range
discrimination
A longer pulse carries more energy for distant targets, but it smears close
targets on the same bearing together.
Page 4 of 63
