Communication Systems/Analog Modulation Introduction

Analog Modulation Overview

Let's take a look at a generalized sinewave:

$x\left(t\right)=A\sin \left({\omega t+\theta }\right)$

It consists of three components namely; amplitude, frequency and phase. Each of which can be decomposed to provide finer detail:

$x(t)=As(t)\sin(2\pi [f_{c}+kf_{m}(t)]t+\alpha \phi (t))$

Types of Analog Modulation

We can see 3 parameters that can be changed in this sine wave to send information:

• $As(t)$. This term is called the "Amplitude", and changing it is called "Amplitude Modulation" (AM)
• $kf_{m}(t)$ This term is called the "Frequency Shift", and changing it is called "Frequency Modulation"
• $\alpha \phi (t)$. this term is called the "Phase angle", and changing it is called "Phase Modulation".
• The terms frequency and phase modulation are often combined into a more general group called "Angle Modulation".

The Breakdown

Each term consists of a coefficient (called a "scaling factor"), and a function of time that corresponds to the information that we want to send. The scaling factor out front, A, is also used as the transmission power coefficient. When a radio station wants their signal to be stronger (regardless of whether it is AM, FM, or PM), they "crank-up" the power of A, and send more power out onto the airwaves.

How we Will Cover the Material

We are going to go into separate chapters for each different type of modulation. This book will attempt to discuss some of the mathematical models and techniques used with different modulation techniques. It will also discuss some practical information about how to construct a transmitter/receiver, and how to use each modulation technique effectively.