What is the function of a reactance modulator?

A reactance modulator is a circuit used in transmitters to generate Frequency Modulation (FM) or Phase Modulation (PM). It achieves this by utilizing a component whose reactance—either capacitance or inductance—varies in response to an applied audio voltage. A varactor diode is a very common component used for this exact purpose. When the modulating audio signal changes the capacitance in the oscillator's resonant tank circuit, the oscillator's frequency shifts proportionally. This continuous shifting of the carrier frequency creates the FM signal. Options suggesting Amplitude Modulation (AM) or varying resistance are incorrect. Reactance specifically refers to the frequency-dependent properties of capacitors and inductors, not resistors. Furthermore, varying reactance alters the frequency or phase of the carrier, not its overall amplitude.