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RADIO COMMUNICATIONS
IN THE DIGITAL AGE
VOLUME ONE:
HF TECHNOLOGY

HF Handbook in PDF Zipped

First Printing, May 1996
Copyright © 1996
By Harris Corporation
All rights reserved
LIBRARY OF CONGRESS CATALOG CARD NUMBER: 96-94476
Harris Corporation, RF Communications Division
Radio Communications in the Digital Age
Volume One: HF Technology
Printed in USA
5/96 MG 25K
B1006
© Harris Corporation
All Harris RF Communications products and systems included herein are trademarks of the Harris Corporation.

TABLE OF CONTENTS

INTRODUCTION

CHAPTER 1 PRINCIPLES OF RADIO COMMUNICATIONS

CHAPTER 2 THE IONOSPHERE AND HF PROPAGATION

CHAPTER 3 ELEMENTS IN AN HF RADIO SYSTEM

CHAPTER 4 NOISE AND INTERFERENCE

CHAPTER 5 DATA COMMUNICATION VIA HF RADIO

CHAPTER 6 ADAPTIVE RADIO TECHNOLOGY

CHAPTER 7 SECURING COMMUNICATIONS

CHAPTER 8 HF SYSTEMS AND APPLICATIONS

CHAPTER 9 FUTURE DIRECTIONS

APPENDIX A STANDARDS

APPENDIX B GLOSSARY

FURTHER READING

Note: Throughout this handbook, technical terms and acronyms shown in italics are defined in the Glossary, Appendix B.

INTRODUCTION

There was a time when radio communication was one of a few methods for instant communication across distances. We’ve all seen black-and-white wartime film clips of radio operators sending Morse code using bulky radio equipment. After World War II, the communications industry turned its attention to other technologies, leading to a period of slow growth in high-frequency (HF) radio communications during the 1960s and 1970s.
However, HF, also known as short wave, is now undergoing an exciting revival propelled by an infusion of new technology.

Genesis

Modern radio technology had its birth with the publication of James Clerk Maxwell’s Treatise on Electricity and Magnetism in 1873, setting forth the basic theory of electromagnetic wave propagation. But the first radio waves were actually detected 15 years later. In 1888, Heinrich Rudolph Hertz (the scientist for whom the unit of frequency is named) demonstrated that disturbances generated by a spark coil showed the characteristics of Maxwell’s radio waves. His work inspired Guglielmo Marconi’s early experiments with wireless telegraphy using Morse code. By 1896, Marconi had communicated messages over distances of a few kilometers. It was thought at the time that radio waves in the atmosphere traveled in straight lines and that they therefore would not be useful for over-the-horizon communication. That opinion did not discourage Marconi, however, who became the first to demonstrate the transmission of radio waves over long distances. In 1901 in Newfoundland, Canada, he detected a telegraphic signal transmitted from Cornwall, England, 3,000 kilometers away. For an antenna, he used a wire 120 meters long, held aloft by a simple kite. Marconi’s success stimulated an intensive effort to explain and exploit his discovery. The question of how radio waves could be received around the surface of the earth was eventually answered by Edward Appleton. It was this British physicist who discovered that a blanket of electrically charged, or “ionized,” particles in the earth’s atmosphere (the ionosphere) were capable of reflecting radio waves. By the 1920s, scientists had applied this theory and developed ways to measure and predict the refractive properties of the ionosphere.

Growth

In time, the characteristics of HF radio propagation became better understood. Operators learned, for example, that usable frequencies varied considerably with time of day and season. HF technology developed quickly. By World War II, HF radio was the primary means of long-haul communications for military commanders because it provided communications with land, sea, and air forces. In the hands of a skilled operator, armed with years of experience and an understanding of the propagating effects of the ionosphere, HF radio was routinely providing reliable, effective links over many thousands of miles. Today, HF radio plays an important role in allowing emerging nations to establish a national communications system quickly and inexpensively.

Hiatus

The advent of long-range communications by satellite in the 1960s initiated a period of declining interest in HF radio. Satellites carried more channels and could handle data transmission at higher speeds. Additionally, satellite links seemed to eliminate the need for highly trained operators. As long-range communications traffic migrated to satellites, HF was often relegated to a backup role. The result was user preference for wider bandwidth methods of communication, such as satellites, resulting in declining proficiency in HF as the number of experienced radio operators decreased. It became clear over time, however, that satellites (for all their advantages) had significant limitations. Military users became increasingly concerned about the vulnerability of satellites to jamming and physical damage, and questioned the wisdom of depending exclusively on them. Moreover, satellites and their
supporting infrastructure are expensive to build and maintain.

Revival

In the last decade, we’ve seen a resurgence in HF radio. Research and development activity has intensified, and a new generation of automated HF equipment has appeared. These systems provide dramatic improvements in link reliability and connectivity, while eliminating the tedious manual operating procedures required to use older generation equipment. Today’s adaptive HF radios are as easy to use as wireless telephones. Nonetheless, the perception that HF radio is an inherently difficult medium continues to linger. This perception continues only because some communicators remember how HF used to be. As your interest in this book shows, however, HF is again being recognized as a robust and highly competitive medium for long-haul communications, offering myriad capabilities. In this introduction to HF radio communications, we present information that will help you understand modern HF radio technology. We’ll cover the principles of HF radio, talk about specific applications, and then, consider the future of HF radio communication.