Question

On radiating (sending out) an AM modulated signal, the total radiated power is due to energy carried by ω_c, ω_c – ωm and ω_c + ω_m. Suggest ways to minimise cost of radiation without compromising on information.

Answer 1

Sideband frequencies: The AM wave contains three frequencies ω_c, (ω_c + ω_m) and (ω_c – ω_m), ω_c is called carrier frequency, (ω_c + ω_m) and ( ω_c – ω_m) are called sideband frequencies.

(ω_c + ω_m) = Upper sideband (USB) frequency

(ω_c – ω_m) =Lower sideband (LSB) frequency

Sideband frequencies are generally close to the carrier frequency.

Only side band frequencies contain information in amplitude modulated signal, [only (ω_c+ ω_m) and (ω_c + ω_m)].

Here, the total radiated power is due to energy carried by ω_c, (ω_c – ω_m) and (ω_c+ω_m)

For reduction of the cost of radiation without compromising on information, ω_c can be left and transmit the frequencies (ω_c + ω_m), (ω_c – ω_m) or both (ω_c + ω_m) and (ω_c – ω_m).