Modulation Methods

Abstract

A signal created by any device such as a microphone pickup, a transducer, a computer terminal, etc., may be in either analog or digital form as seen in Figure 5.1. Analog signals have continuously varying amplitudes while digital signals consist of discrete pulses. These signals, whether digital or analog, are called baseband signals. In Chapter 3 it was shown that baseband signals cannot be transmitted for any appreciable distance over a communication link. These signals suffer distortion effects which are in large measure due to the presence of low-frequency components in the signal. A process known as modulation is used to allow communication to take place more efficiently over longer distances.