Analog Communication - ANGLE MODULATION & DEMODULATION

Information about Analog Communication - ANGLE MODULATION & DEMODULATION

Published on August 10, 2014

Author: psureshvenugopal

Source: authorstream.com

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ANGLE MODULATION: ANGLE MODULATION Angle Modulation: Angle Modulation Introduction Types of Angle Modulation – FM & PM Definition – FM & PM Signal Representation of FM & PM Generation of PM using FM Generation of FM using PM Angle Modulation: Angle Modulation Consider again the general carrier represents the angle of the carrier. There are two ways of varying the angle of the carrier. By varying the frequency ,  c – Frequency Modulation . By varying the phase ,  c – Phase Modulation Frequency Modulation: Frequency Modulation Phase Modulation: Phase Modulation One of the properties of a sinusoidal wave is its phase , the offset from a reference time at which the sine wave begins. We use the term phase shift to characterize such changes. If phase changes after cycle k , the next sinusoidal wave will start slightly later than the time at which cycle k completes. Introduction to Angle Modulation: Introduction to Angle Modulation High degree of noise immunity by bandwidth expansion. They are widely used in high-fidelity music broadcasting . T hey are of constant envelope , which is beneficial when amplified by nonlinear amplifiers. Introduction to Angle Modulation: Introduction to Angle Modulation FM and PM: FM and PM FREQUENCY MODULATION: FREQUENCY MODULATION Frequency Modulation (FM): Frequency Modulation (FM) Types of FM Spectrum of FM Transmission Bandwidth of FM Deviation Ratio Generation of FM Detection of FM Signal to Noise Ratio of FM Pre-Emphasis & De-Emphasis in FM Types of FM: Types of FM Basically 2 types of FM: NBFM (Narrow Band Frequency Modulation) WBFM (Wide Band Frequency Modulation) NBFM: NBFM Derivation Difference between NBFM & AM DSB FC Generation of NBFM WBFM: WBFM Generating WBFM from NBFM Derivation Bessel Function Spectrum of FM: Spectrum of FM Transmission Bandwidth of FM: Transmission Bandwidth of FM Carson’s Rule: Carson’s Rule Deviation Ratio: Deviation Ratio Power in FM: Power in FM Generation of FM: Generation of FM Mainly there are 2 methods to generate FM Signal. They are: Direct Method Hartley Oscillator Basic Reactance Modulator Indirect Method Amstrong Modulator (Using NB Phase Modulator) Frequency Multiplier Generation of FM: Generation of FM Basically two methods: Direct method Build a voltage controlled oscillator (VCO) where the frequency is varied in response to an applied modulating voltage by using a voltage-variable capacitor The main difficulty is that it is very difficult to maintain the stability of the carrier frequency of the VCO when used to generate wide-band FM. Indirect method Use a narrow-band FM modulator followed by frequency multiplier and mixer for up conversion. Allows to decouple the problem of carrier frequency stability from the FM modulation. Edwin Howard Armstrong (1890 - †1954): Edwin Howard Armstrong (  1890 - †1954) Edwin Howard Armstrong received his engineering degree in 1913 at t he Columbia University. He was the inventor of the following basic electronic circuits underlying all modern radio, radar, and television: Regenerative Circuit ( 1912) Superheterodyne Circuit ( 1918) Superregenerative Circuit ( 1922) FM System (1933). Indirect Method – Amstrong Modulator: Indirect Method – Amstrong Modulator Indirect Method: Indirect Method Narrow Band Phase Modulator (NBPM): Narrow Band Phase Modulator (NBPM) Detection of FM: Detection of FM Types of FM Detectors: RL Discriminator Tuned FM Discriminator Balanced Slope Detector Centre Tuned Discriminator / Phase Discriminator / Foster – Seeley Discriminator Phase Locked Loop (PLL) Demodulator Ratio Detector RL Discriminator: RL Discriminator Signal to Noise Ratio of FM: Signal to Noise Ratio of FM Introduction to Signal to Noise Ratio (SNR) Noise in FM Capture Effect FM Threshold Effect FM Threshold Reduction Pre-Emphasis & De-Emphasis in FM

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