FCC Exam Question: 3-59H4

Which of the following best describes a pulse modulation system?

A. The peak transmitter power is normally much greater than the average power.
B. Pulse modulation is sometimes used in SSB voice transmitters.
C. The average power is normally only slightly below the peak power.
D. The peak power is normally twice as high as the average power.
Correct Answer: A

Explanation: Pulse modulation systems transmit radio frequency (RF) energy in short, discrete bursts or pulses. The peak transmitter power refers to the maximum power level achieved *during* these brief pulse durations. However, these pulses are often separated by significant periods of little to no transmission, meaning the system has a low "duty cycle" (the fraction of time the transmitter is actively sending a pulse). The average power is calculated over a longer period, taking into account both the high-power pulse durations and the low-power or zero-power off-periods. Therefore, due to the typically low duty cycle, the average power for a pulse modulation system is normally much lower than its peak power. Option B is incorrect because Single Sideband (SSB) voice transmitters use continuous amplitude and phase variations, not discrete RF pulses. Options C and D are incorrect because the average power in a pulse modulation system is often *substantially* lower than the peak power, frequently by factors far greater than two, due to the typically low duty cycle.

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Includes Elements 1, 3, 6, 7R, 8, and 9.