The Froehlich/Kent Encyclopedia of Telecommunications

Volume 6 - Digital Microwave Link Design to Electrical Filters

Fritz E. Froehlich, Allen Kent

• Publisher: CRC Press
• Year: 2021
• eBook ISBN: 9781000447828
• Topic: Computer Science
• Subtopic: Information Technology
• Index: Computer Science

"The only continuing source that helps users analyze, plan, design, evaluate, and manage integrated telecommunications networks, systems, and services, The Froehlich/Kent Encyclopedia of Telecommunications presents both basic and technologically advanced knowledge in the field. An ideal reference source for both newcomers as well as seasoned specialists, the Encyclopedia covers seven key areas--Terminals and Interfaces; Transmission; Switching, Routing, and Flow Control; Networks and Network Control; Communications Software and Protocols; Network and system Management; and Components and Processes."

Electrical Filters

Introduction

History

An electrical filter is a device that transforms a given input signal into a desired output signal. The transformation or filtering may be carried out in the frequency or time domain by a variety of physical means (electrical, mechanical, acoustical, etc.) depending on the frequency range of the signals and on the application in question. The most commonly used electrical filters traditionally have been wave or frequency filters; this explains why most literature on electrical filters is based on the theory and practice of frequency filters.

Electrical frequency filters are frequency-selective networks designed to "pass" or transmit sinusoidal waves in one or more continuous frequency bands (pass band) and to "stop," reject, or attenuate sinusoidal waves in the complementary bands ("stop band"). Filters with single pass bands typically are classified as low-pass, high-pass, and band-pass, depending on the bands of frequencies passed. For example, the pass band of the band-pass filter in Fig. 1 extends from frequency ω₁ to ω₂ (where ω is the angular frequency expressed in radians per second and is equal to the frequency f in cycles per second, or hertz (Hz), multiplied by 2π). There are other filter types, such as all-pass, frequency-emphasizing, and frequency-rejection filters, all of which are discussed in more detail below.

Filters are among the most important components of present-day communications systems. For example, in the common radio receiver, filters are used to smooth out the pulsating direct current (DC) from the rectifier to give a steady output of the power supply. In superheterodyne receivers, filters in the intermediate frequency stages provide the desired selectivity. Telephone carrier circuits are possible only because of filters used to separate the various channels and to route the signals to the proper paths. In fact, while filters generally are used very widely, the telephone systems traditionally have been among the biggest users. However, with the trend toward digital integrated circuits and the development of the Integrated Services Digital Networks (ISDNs), frequency selective filters largely are being repla...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Contents of Volume 6
• Contributors to Volume 6
• Digital Microwave Link Design
• Digital Microwave Radio
• Digital Modulation and Coding
• Digital Modulation Techniques
• Digital Radio Systems
• Digital Signal Processing
• Digital Speech Processing
• Digital Switching Systems
• Distortion and Noise in Telephone Systems. See Analog and Digital Distortion in Speech and Data Transmission
• Divestiture impact on Local Telephone Rate Policy in the United States: Diffusion of Local Measured Service, 1977-1985
• Divestiture of Bell Operating Companies: Technical Challenges and Achievements
• Dolbear, Amos Emerson
• DS1 Services and Standards
• Echo-Canceling Algorithms
• Echo Suppressors
• Economic Theories of Regulation in Telecommunications
• Electrical Filters