A variable frequency oscillator in electronics is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio transmitter and in receivers that work by
A Heathkit amateur radio transmitter circa 1969, with external VFO
Signal modulation
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Signal modulation is the process of varying one or more properties of a periodic waveform in electronics and telecommunication for the purpose of transmitting information.
Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown.
A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong sidebands are apparent; in principle, an infinite number are produced in FM, but the higher-order sidebands are of negligible magnitude.