Pulse Modulation and Amplitude Modulation
What is Modulation?
Modulation is the process of converting the signal to be transmitted into radio waves by adding it to an optical carrier signal. The frequency of the signal to be transmitted to the receiver is usually low. The carrier signal has a constant frequency and amplitude. The low-frequency signal is superimposed with a high-frequency carrier wave.
Advantages of Modulation
1. The size of the antenna can be reduced
2. The mixing of signals can be avoided
3. The range of communication increases
4. Improves the quality of reception
5. The bandwidth can be adjusted
Amplitude modulation is a continuous wave modulation. The amplitude of the carrier wave is varied in accordance with the signal wave. The frequency and phase of the wave are kept constant.
Advantages of Amplitude Modulation
1. Wave can be transmitted over a longer distance in amplitude modulation
2. Simple and low-cost circuits can be used in amplitude modulation, unlike frequency modulation.
3. It requires limited bandwidth.
Disadvantages of Amplitude Modulation
1. Amplitude modulation is susceptible to noise generation
2. The quality of the signal is not good
3. More power is required during modulation since it requires more than twice the amplitude-frequency to modulate the signal with a carrier.
Application of Amplitude Modulation
1. It is used in Navy and Aviation for communication as it can travel over a longer distance.
2. It is used to transmit Morse code using radio and other communication systems.
The pulse modulation technique deals with discrete signals. The continuous signals can be converted to discrete signals by a process called Sampling. The pulse modulation is of different types
Pulse Code Modulation (PCM)
Pulse Code Modulation is a digital modulation technique. This is the method to convert the analog signal to a digital signal so that the modified analog signal can be transmitted through the digital communication system. Pulse Code Modulation (PCM) is in binary form, so there is only two possible states high and low (0 and 1). The analog signal can be got back by a process called demodulation. PCM is used in compressing the data and storing it in DVD, CDs etc. They are also used in mobile phones, remote-controlled cars, planes etc.
Pulse Amplitude Modulation (PAM)
This is the technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. This is an analog type of modulation. Pulse Amplitude modulation is of two types
1. Flat Top PAM: The amplitude of each pulse is directly proportional to modulating signal amplitude at the time of pulse occurrence and then keeps the amplitude for the rest of the half-cycle.
2. Natural PAM: The amplitude of each pulse is directly proportional to the instantaneous modulating signal amplitude at the time of pulse occurrence and then follows the amplitude of the modulating signal for the rest of the half-cycle.
Pulse Position Modulation (PPM)
The position of the carrier signal is varied in proportion to the instantaneous value of the analog signal.
Pulse Width Modulation (PWM)
The width of the pulses (the carrier signal) is varied in proportion to the instantaneous values of the analog signal.