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Question
On radiating (sending out) an AM modulated signal, the total radiated power is due to energy carried by ωc, ωc – ωm and ωc + ωm. Suggest ways to minimise cost of radiation without compromising on information.
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Solution
Sideband frequencies: The AM wave contains three frequencies ωc, (ωc + ωm) and (ωc – ωm), ωc is called carrier frequency, (ωc + ωm) and ( ωc – ωm) are called sideband frequencies.
(ωc + ωm) = Upper sideband (USB) frequency
(ωc – ωm) =Lower sideband (LSB) frequency
Sideband frequencies are generally close to the carrier frequency.
Only side band frequencies contain information in amplitude modulated signal, [only (ωc+ ωm) and (ωc + ωm)].
Here, the total radiated power is due to energy carried by ωc, (ωc – ωm) and (ωc+ωm)
For reduction of the cost of radiation without compromising on information, ωc can be left and transmit the frequencies (ωc + ωm), (ωc – ωm) or both (ωc + ωm) and (ωc – ωm).
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