Question
What is the function of a reactance modulator?
Answer Options
- A) Produce PM or FM signals by varying a resistance
- B) Produce AM signals by varying an inductance
- C) Produce AM signals by varying a resistance
- D) Produce PM or FM signals by varying a capacitance
Correct Answer: D
Explanation
A reactance modulator is a circuit that produces either Phase Modulation (\text{PM}) or Frequency Modulation (\text{FM}) by using the audio input signal to electronically change a reactive component (inductor or capacitor) in an oscillator circuit. This change in reactance shifts the resonant frequency of the oscillator.
The function of a reactance modulator is to produce \text{PM} or \text{FM} signals by varying a capacitance (or inductance). The audio signal controls the conduction of a transistor or FET, which is wired to exhibit a variable capacitive (or inductive) reactance. This variable reactance is inserted into the master oscillator tank circuit, causing the instantaneous frequency to change as dictated by the audio signal.
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