BasicB-003-002-003
An FM transmitter's modulator:
B
Answer
Basic radio theory
Type
A
alters the radio's output signal amplitude
B
affects the frequency of the oscillator
C
as no effect on the frequency of the oscillator
D
produces amplitude changes in the oscillator
Answer Notes
In Frequency Modulation (FM), the information (audio) is transmitted by varying the instantaneous frequency of the carrier wave. The modulator is the circuit responsible for taking the amplified audio signal and using it to shift the frequency of the transmitter's oscillator.
As the audio signal voltage goes up and down, the modulator causes the oscillator's frequency to deviate slightly above and below its center frequency. This is the defining characteristic of an FM transmission.
Options suggesting the modulator alters amplitude are describing Amplitude Modulation (AM), not FM. Therefore, the modulator strictly affects the frequency, not the power output or amplitude of the oscillator.
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The microphone of an FM transmitter:
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How is the oscillator in the FM transmitter different from oscillators in AM, CW, and SSB transmitters?