Ham Radio General Class Practice Test

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What emission is produced by a reactance modulator connected to an RF power amplifier?

Multiplex modulation
Phase modulation
Amplitude modulation
Pulse modulation

The correct answer is: Phase modulation

A reactance modulator is designed to vary the phase of the radio frequency (RF) signal without altering its amplitude significantly. This modulation technique works by changing the reactance (the opposition to change in current) presented to the RF signal, effectively manipulating the phase of the signal being output by the RF power amplifier. The changes in phase modify the instantaneous frequency of the RF signal, resulting in phase modulation. Phase modulation is particularly useful in many applications, including digital signal transmission, because it can be more resistant to noise compared to amplitude modulation. In contrast, amplitude modulation alters the signal's strength, which can make it more susceptible to interference and can reduce signal quality. Therefore, for a reactance modulator connected to an RF power amplifier, the correct emission produced is phase modulation.