Amplitude modulation
Amplitude modulation is a family of a continuous-wave(CW)modulation systems.In amplitude modulation,the amplitude of a sinusoidal carrier wave is varied in accordance with the baseband (modulating) signal.Amplitude modulation may be defined as a system in which the maximum amplitude of the carrier wave is made proportional to the instantaneous value(amplitude)of the modulating or baseband signal.In amplitude modulation the maximum amplitude of the carrier wave is made proportional to the instantaneous value of the modulating signal.
In mathematically,
Let us consider a sinusoidal carrier wave c(t) given as
c(t)= A cos ωct
where,
ωc is the carrier frequency .
A is a the maximum amplitude of carrier wave.
The standard equation for amplitude modulated(AM)wave may be expressed as
s(t)=x(t) cosωct + A cosωct .................................(1)
s(t)=[A +x(t)] cosωct ..........................................(2)
equation number (2) is a required equation for a Amplitude modulation.
Few points about Amplitude Modulation (AM):
(i) It may be observed that equation (1) or(2) describes the time-domain behaviour of amplitude-modulated signal.
(ii)It may be noted that carrier signal [i.e.c(t)=A cosωct] is a fixed frequency signal having frequency ωc.The modulating or baseband signal x(t) contains the information or intelligence to be transmitted.In the process of amplitude modulation,this information is superimposed upon the carrier signal in the form of amplitude variation of the carrier signal. This means that the information to be transmitted,is now,contained in the amplitude variation of the carrier signal.In other words,in amplitude modulation,the information is transmitted in the form of amplitude variations of the carrier signal.
(iii)The resulting signal from the process of amplitude-modulation is called amplitude modulated signal or simply AM wave.
(iv)In the process of amplitude modulation,the frequency and phase of the carrier remain constant whereas the maximum amplitude varies according to the instantaneous value of the information signal.
(v)equation 2 represents an amplitude modulated wave.this wave has a constant frequency
ωc and amplitude A + x(t).this implies that the amplitude of the wave is changing around A in accordance with the value of the modulating signal x(t).the frequency of the AM signal remains unchanged and is equal to ωc.
(vi)The AM wave has a time-varying amplitude called as the envelope of the AM wave.This means that the unique property of AM is that the envelope of the modulated carrier has the same shape as the message signal or baseband signal.
SINGLE TONE MODULATION:
amplitude modulation in which we assumed that baseband or modulating signal is a random signal which contains a large number of frequency components. This means that a carrier signal(fixed frequency signal) is modulated by a larger number of frequency components.
amplitude modulation in which the modulating or baseband signal consists of only one(single)frequency i.e.modulation is done by a single frequency or tone. this type of modulation is known as single tone amplitude modulation.
Few points about Amplitude Modulation (AM):
(i) It may be observed that equation (1) or(2) describes the time-domain behaviour of amplitude-modulated signal.
(ii)It may be noted that carrier signal [i.e.c(t)=A cosωct] is a fixed frequency signal having frequency ωc.The modulating or baseband signal x(t) contains the information or intelligence to be transmitted.In the process of amplitude modulation,this information is superimposed upon the carrier signal in the form of amplitude variation of the carrier signal. This means that the information to be transmitted,is now,contained in the amplitude variation of the carrier signal.In other words,in amplitude modulation,the information is transmitted in the form of amplitude variations of the carrier signal.
(iii)The resulting signal from the process of amplitude-modulation is called amplitude modulated signal or simply AM wave.
(iv)In the process of amplitude modulation,the frequency and phase of the carrier remain constant whereas the maximum amplitude varies according to the instantaneous value of the information signal.
(v)equation 2 represents an amplitude modulated wave.this wave has a constant frequency
ωc and amplitude A + x(t).this implies that the amplitude of the wave is changing around A in accordance with the value of the modulating signal x(t).the frequency of the AM signal remains unchanged and is equal to ωc.
(vi)The AM wave has a time-varying amplitude called as the envelope of the AM wave.This means that the unique property of AM is that the envelope of the modulated carrier has the same shape as the message signal or baseband signal.
SINGLE TONE MODULATION:
amplitude modulation in which we assumed that baseband or modulating signal is a random signal which contains a large number of frequency components. This means that a carrier signal(fixed frequency signal) is modulated by a larger number of frequency components.
amplitude modulation in which the modulating or baseband signal consists of only one(single)frequency i.e.modulation is done by a single frequency or tone. this type of modulation is known as single tone amplitude modulation.
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