Download
1 / 43
E N D
Directorate of Technical Education, Tamilnadu. Thanthai Periyar Government Institute of Technology, Vellore–632002 Department of ECE
Amplitude modulation Unit 1 Presented by Mrs. M.P.Sasirekha
Noise • Noise is an unwanted signal which interferes with the original message signal and corrupts the parameters of the message signal. • This alteration in the communication process, leads to the message getting altered. • It is most likely to be entered at the channel or the receiver.
Noise • it is understood that noise is some signal which has no pattern and no constant frequency or amplitude. It is quite random and unpredictable. Measures are usually taken to reduce it, though it can’t be completely eliminated.
Most common examples of noise are • Hiss sound in radio receivers • Buzz sound amidst of telephone conversations • Flicker in television receivers, etc.
Effects of Noise • Noise limits the operating range of the systems. • Noise limits the smallest signal that a receiver is capable of processing. • Noise affects the sensitivity of receivers • Sensitivity is the minimum amount of input signal necessary to obtain the specified quality output. Noise affects the sensitivity of a receiver system, which eventually affects the output.
Two general categories • Noise can be divided into two general categories: • (i) Correlated Noise : Implies a relationship between the signal and the noise. • (ii) Uncorrelated Noise : It is present all the time whether there is a signal or not. • Uncorrelated Noise: • Uncorrelated can be divided into two general categories: (i) External noise and (ii) Internal noise.
EXTERNAL NOISE, INTERNAL NOISE • External Noise: • It is a Noise generated outside the device or circuit. There are three primary sources of external noise. • (i) Atmospheric , • (ii) Extra terrestrial and • (ii) Manmade noise. • Extraterrestrial Noise consists of electrical signals that originate from outside earths atmosphere and is therefore also called as deep space noise. This noise originates from the milky way , other galaxies and the sun.
Extraterrestrial noise • Extraterrestrial noise is subdivided into two categories.: (i) Solar and (ii) Cosmic. • Internal Noise: It is the noise caused by electrical interference generated within a device or circuit. • There are three primary kinds of internally generated noise are: (i) Thermal. (ii) Shot ,Transits time.
INTRODUCTION TO COMMUNICATION SYSTEM • Communication is the process of establishing connection (or link) between two points for information exchange. • The Science of Communications involving long distances is called Telecommunication ( the world Tele standing for long distance)
Two basic types of communication • The Two basic types of communication systems are (i) Analog. (ii) Digital. • In Analog Systems: Both the information and the carrier are analog signals. • In Digital Systems: The digital pulses are transferred between two or more points in a communication system
Analog communication • The modulation systems or techniques in which one of the characteristics of the carrier is changed in proportion with the instantaneous value of modulating signal is called analog communication system.
Advantages of Analog communications • Transmitters and Receivers are simple • Low bandwidth requirement • FDM can be used
Disadvantages of analog communication • Noise affects the signal quality • It is not possible to separate noise and signal • Repeaters can‘t be used between transmitters and receivers • Coding is not possible • It is not suitable for the transmission of secret information
Amplitude modulation • Amplitude Modulation is defined as changing the amplitude of the carrier signal with respect to the instantaneous change in message signal.
Under modulated Modulation index less than 1.
Over modulated Modulation index greater than 1
Bandwidth • It is the amount of data that can be transferred from one point to another within a network in a specific amount of time. It is measured in bits per second.
Signal-to-noise ratio • Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. • SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. • The higher the value of SNR, the greater will be the quality of the received output.
Signal-to-noise ratio • Input SNR = (SNR)I=Average power of modulating signal / Average power of noise at input • Output SNR = (SNR)O=Average power of demodulated signal / Average power of noise at output • Channel SNR = (SNR)C=Average power of modulated signal / Average power of noise in message bandwidth.
Advantages and Disadvantages • Advantages: • The modulation process is very simple • No need for filtering during modulation for sidebands. • Disadvantages • Demodulation need coherent carrier source. • It carrier less information about the carrier. • Carrier power is wasted • Envelop detection is not possible. • High bandwidth compares to SSB, VSB.
Reference • https://www.tutorialspoint.com/principles_of_communication/principles_of_communication_noise.htm
