FCC Exam Question: 8-4A3

A pulse RADAR transmits a 0.5 microsecond RF pulse with a peak power of 100 kilowatts every 1600 microseconds. This RADAR has:

A. An average power of 31.25 watts.
B. A PRF of 3,200.
C. A maximum range of 480 kilometers.
D. A duty cycle of 3.125 percent.
Correct Answer: A

Explanation: The average power of a pulse RADAR is calculated by multiplying its peak power by its duty cycle. First, calculate the duty cycle (DC): DC = Pulse Width (τ) / Pulse Repetition Interval (PRI) DC = 0.5 microseconds / 1600 microseconds = 0.0003125 Next, calculate the average power: Average Power = Peak Power * Duty Cycle Average Power = 100 kilowatts * 0.0003125 = 100,000 watts * 0.0003125 = 31.25 watts. Therefore, option A is correct. Let's examine the other options: B) The Pulse Repetition Frequency (PRF) is 1 / PRI = 1 / (1600 * 10^-6 s) = 625 Hz, not 3,200. C) The maximum unambiguous range is (speed of light * PRI) / 2 = (300,000 km/s * 0.0016 s) / 2 = 240 km, not 480 km. D) The duty cycle as a percentage is 0.0003125 * 100% = 0.03125%, not 3.125%.

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