BasicB-003-002-004
How is the oscillator in the FM transmitter different from oscillators in AM, CW, and SSB transmitters?
D
Answer
Basic radio theory
Type
A
It has higher fidelity
B
The modulator changes its output amplitude
C
It runs at much higher frequencies
D
The modulator alters its frequency
Answer Notes
In Frequency Modulation (FM), the information (audio) is transmitted by varying the frequency of the carrier wave. To achieve this, the modulator acts directly on the oscillator to shift its output frequency slightly above and below the center frequency in response to the audio signal.
This fundamentally differs from Amplitude Modulation (AM), Single Sideband (SSB), or Continuous Wave (CW) transmitters, where the oscillator generates a steady, unvarying carrier frequency. In those modes, the amplitude is altered by the modulator or interrupted by a key, while the base frequency remains stable.
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An FM transmitter's modulator:
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In an FM transmitter, the frequency multiplier: