HF Handbook in PDF Zipped
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
© Harris Corporation
All Harris RF Communications products and systems included herein are trademarks of the Harris Corporation.
TABLE OF CONTENTS
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
Note: Throughout this handbook, technical terms and acronyms shown in italics are defined in the Glossary, Appendix B.
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.
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.
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.
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.
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.