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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.