Question

Briefly Explain About Amplitude Demodulation

Answer 1

Amplitude Demodulation

1. "Amplitude Modulation" refers to a modulation procedure in which the amplitude of the carrier varies with respect to the instantaneous value of the modulating signal
   
2. A primary motivation for modulation in the context of communications would be to facilitate the transmission of this information-carrying signal over a communication channel or radio station via a specified pass-band.
3. Based on this, we can divide continuous-wave modulation into two broad categories: amplitude modulation and angle modulation.
4. Both of these modulations distinguish themselves by providing spectrally distinct features and, as a result, distinct functional advantages. The classification is completed based on whether the amplitude of the sinusoidal carrier wave, or its frequency or phase angle, varies in nature with the information signal.

Concepts of Amplitude Modulation:

Consider a carrier signal is characterized by,

The carrier signal amplitude is represented by $A_C$, and the carrier signal frequency is represented by $f_c$.

$m\left(t\right)$represents the information or message signal. As a result, an amplitude-modulated

($AM$) wave can be described as a function of time as follows:

$s\left(t\right)=A_c[1+K_{a}m(t\left)\right]\cos \left(2\pi f_{c}t\right)$

The amplitude sensitivity is denoted by the constant $K_a$. The carrier amplitude and message signal are both expressed in volts, while amplitude sensitivity is expressed in $vol{t}^{-1}$

In general, the amplitude of |Kam(t)| is less than unity:

$K_{a}m\left(t\right)|<1,$ for all $t$

The carrier freq. ( $f_c$ ) is much higher than the maximum frequency element represented by $W$ of the message signal $m\left(t\right)$

$f_c>>W$

The maximum freq. of the Amplitude modulation wave for +ve freq. is equal to ($f_c+W$), and the lowest freq. element is equal to ($f_c-W$). The difference between these two frequency terms is known as the amplitude modulation wave's transmission bandwidth ($B_T$), which is exactly double the message signal bandwidth ($W$). So,

$B_T=2W$