What is the spectrum of AM wave?
The frequency band used for AM radio is about 550 to 1720 kHz. This is the range of carrier frequencies available. The information transmitted is music and talk which falls in the audio spectrum. The full audio spectrum ranges up to 20 kHz, but AM radio limits the upper modulating frequency to 5 kHz.
What is the equation of AM?
If the modulation index μ=1 then the power of AM wave is equal to 1.5 times the carrier power. So, the power required for transmitting an AM wave is 1.5 times the carrier power for a perfect modulation.
How to find the spectrum of AM wave?
To find the spectrum of AM wave, we take its Fourier transform. The fourier transform of s (t) may be found by considering the two factors x (t) cos ω c t and A cos ω c t separately as follows: To find the Fourier transform of x (t) cos ω c t , we first note the frequency-shifting theorem of Fourier transform as :
Which is part of the spectrum contains shifted spectrum?
Thus the spectrum of modulated signal contains shifted spectrum of modulating signal and the spectrum of carrier signal as shown in figure 1 (c) . For positive frequencies, a portion of the spectrum of AM wave is lying above the carrier frequency ω c .
How are negative frequencies represented in the spectrum?
For negative frequencies, the upper sideband (USB) is represented by the portion of the spectrum below -ω c and the lower sideband by the symmetrical portion above -ω c . Two sidebands have been shown in figure 1 (c). We generally keep ω c > ω m which ensures that the two sidebands do not overlap each other.
Which is the highest frequency in the AM wave?
From figure, it is obvious that for positive side, the highest frequency component present in the spectrum of AM wave is ω c + ω m and the lowest frequency component is ω c – ω m. Infact, the difference between these two extreme frequencies is equal to the bandwidth of the AM wave.