How can an FM-phone signal be produced in a transmitter?

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Multiple Choice

How can an FM-phone signal be produced in a transmitter?

FM is produced by changing the oscillator’s frequency in response to the audio signal. In an FM transmitter, the audio input drives a mechanism that shifts the tuning of the oscillator (for example, via a varactor diode or a dedicated modulation stage), so the instantaneous frequency follows the modulating waveform. This frequency deviation creates the FM carrier whose frequency sweeps around the center frequency according to the audio. Modulating the power-supply voltage to RF amplifiers would mainly affect amplitude and can distort the signal rather than produce proper frequency modulation. A balanced modulator is used for AM/SSB schemes, not FM. Feeding audio directly to the oscillator succinctly captures the idea of using the audio to vary the oscillator’s frequency, which is the essence of FM generation.

FM is produced by changing the oscillator’s frequency in response to the audio signal. In an FM transmitter, the audio input drives a mechanism that shifts the tuning of the oscillator (for example, via a varactor diode or a dedicated modulation stage), so the instantaneous frequency follows the modulating waveform. This frequency deviation creates the FM carrier whose frequency sweeps around the center frequency according to the audio.

Modulating the power-supply voltage to RF amplifiers would mainly affect amplitude and can distort the signal rather than produce proper frequency modulation. A balanced modulator is used for AM/SSB schemes, not FM. Feeding audio directly to the oscillator succinctly captures the idea of using the audio to vary the oscillator’s frequency, which is the essence of FM generation.

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