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when two frequencies are mixed together, new frequencies
are generated by the mixing process.
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The new frequencies are equal to the sum of and the
difference between the original frequencies.
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when audio frequencies are mixed with radio frequencies,
the new frequencies that are generated are called sidebands.
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the process of mixing audio frequencies with radio
frequencies is called modulation.
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amplitude modulation contains two sidebands and the
carrier.
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single sideband (SSB) is a form of amplitude modulation
where one sideband and the carrier have been removed from the transmitted
signal.
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SSB is more efficient because power is not used to
transmit the carrier and one sideband.
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and second advantage is that the transmitted signal
takes up only half the bandwidth, e.g. 3 kHz not 6 kHz.
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CW occupies the least bandwidth and that FM occupies
the most bandwidth.
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data transmissions commonly use two or more audio
tones to modulate the carrier.
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a variable capacitance diode can be used in an oscillator
to produce frequency modulation (FM).
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excessive audio amplitude or excessive audio bandwidth
into a modulator can cause excessive bandwidth or excessive FM deviation
which may result in interference to adjacent radio frequencies.
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oscillators, mixers and amplifiers can produce harmonics
i.e. multiples of the fundamental frequency.
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harmonics can cause interference to other amateur
bands and other radio users.
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Frequencies that are transmitted other than the wanted
frequency could cause interference to other amateur bands users and
other radio frequency users.
