Download Disadvantages of amplitude modulation

Amplitude Modulation
Amplitude modulation is define as a process in which the amplitude of
the carrier wave c(t) is varied linearly with the base band signal m(t).
Let a sinusoidal carrier wave is denoted by c(t).
c(t) = Accos(2πfct)
where,
Ac= carrier amplitude
fc= carrier frequency
t= time
So, an amplitude modulation (AM) wave as a function of time as follows
S(t) = Ac[1+Kam(t)] cos(2πfct)
Where,
Ka= amplitude sensitivity
m(t)= Base band signal
Amplitude Modulation, AM
Working Principle:
1. We use ACS3-2 on ETEK ACS-3000-02 module. Let J1 be short circuit, J2
be open circuit; i.e R10= 6.8kΩ. Here we use MC1496 AM modulator.
2. At audio signal input port, input 600mV amplitude, 1kHz sine wave freq.: at
carrier signal input port, input 300mV amplitude, 500 kHz sine wave freq.
3. By using oscilloscope we observe on output signal waveforms of AM output
ports. We adjust VR2 so that the signal at AM O/P 1 is maximum without
distortion. Also we adjust VR1 so that the modulation index of the AM signal
reach 50%.
Advantages of Amplitude Modulation
There are several advantages of amplitude modulation, and some of these reasons have
meant that it is still in widespread use today:

It is simple to implement

it can be demodulated using a circuit consisting of very few components

AM receivers are very cheap as no specialised components are needed.
Disadvantages of amplitude modulation
Amplitude modulation is a very basic form of modulation, and although its simplicity is
one of its major advantages, other more sophisticated systems provide a number of
advantages. Accordingly it is worth looking at some of the disadvantages of amplitude
modulation.

It is not efficient in terms of its power usage

It is not efficient in terms of its use of bandwidth, requiring a bandwidth equal to
twice that of the highest audio frequency

It is prone to high levels of noise because most noise is amplitude based and
obviously AM detectors are sensitive to it.
Basic requirements of amplitude modulation :
1. The amplitude of Kam(t) must be less than unity. i.e Kam(t)<1.
2. The carrier freq. fc is always greater than the highest freq. component, w of base
band signal m(t). i.e fc>w.
Demodulation
If we connect the O/P of AM modulated signal to the I/P of AM demodulator, at the
O/P of demodulated. We will get the original base band signal.
AM demodulated signal
Demodulator
Original modulating signal
Now we connect the output signal of the AM modulator to the input port of diode
detector ACS4-1 on ETEK ACS-3000-02 module.
By using oscilloscope we observe on the output signal waveforms of the
demodulated AM output port.
Summary
AM has advantages of simplicity, but it is not the most efficient mode to use, both
in terms of the amount of space or spectrum it takes up, and the way in which it
uses the power that is transmitted. This is the reason why it is not widely used
these days both for broadcasting and for two way radio communication. Even the
long, medium and short wave broadcasts will ultimately change because of the
fact that amplitude modulation, AM, is subject to much higher levels of noise than
are other modes. For the moment, its simplicity, and its wide usage, mean that it
will be difficult to change quickly, and it will be in use for many years to come.