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Subelement O
RADAR
Section 90
RADAR Theory
What is the normal range of pulse repetition rates?
  • 2,000 to 4,000 pps.
  • 1,000 to 3,000 pps.
  • 500 to 1,000 pps.
  • Correct Answer
    500 to 2,000 pps.
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The RADAR range in nautical miles to an object can be found by measuring the elapsed time during a RADAR pulse and dividing this quantity by:
  • 0.87 seconds.
  • 1.15 µs.
  • Correct Answer
    12.346 µs.
  • 1.073 µs.
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What is the normal range of pulse widths?
  • .05 μs to 0.1 μs.
  • Correct Answer
    .05 μs to 1.0 μs.
  • 1.0 μs to 3.5 μs.
  • 2.5 μs to 5.0 μs.
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Shipboard RADAR is most commonly operated in what band?
  • VHF.
  • UHF.
  • Correct Answer
    SHF.
  • EHF.
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The pulse repetition rate (prr) of a RADAR refers to the:
  • Reciprocal of the duty cycle.
  • Pulse rate of the local oscillator.
  • Pulse rate of the klystron.
  • Correct Answer
    Pulse rate of the magnetron.
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If the elapsed time for a RADAR echo is 62 microseconds, what is the distance in nautical miles to the object?
  • Correct Answer
    5 nautical miles.
  • 87 nautical miles.
  • 37 nautical miles.
  • 11.5 nautical miles.

Light travels 186,000 mps, or 161630 nmps. If the radar signal was returned in 62 microseconds, then the distance to the target was reached in half that time, or 31 microseconds. So, the distance to the target is

161630 nmps x 0.000031 secs = 5 nautical miles

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