First Printing,
June 2000
Copyright
© 2000
By Harris
Corporation
All rights
reserved
Library of
Congress Catalog Card Number: 00 132465
Harris Corporation,
RF Communications Division
Radio Communications
in the Digital Age
Volume Two:
VHF/ UHF Technology
Printed in
USA
6/ 00 RO
10K
B2008
© Harris Corporation
All Harris RF Communications products and systems included herein are trademarks of Harris Corporation.
With gratitude to Hal Herrick for his dedication and fortitude in writing this handbook.
TABLE OF CONTENTS
INTRODUCTION 1
CHAPTER 1 PRINCIPLES OF RADIO COMMUNICATIONS
CHAPTER 2 VHF/ UHF RADIO PROPAGATION
CHAPTER 3 ELEMENTS IN A VHF/ UHF RADIO SYSTEM
CHAPTER 4 NOISE AND INTERFERENCE
CHAPTER 5 DATA COMMUNICATION VIA VHF/ UHF RADIO
CHAPTER 7 SECURING COMMUNICATIONS
CHAPTER 8 SYSTEMS AND APPLICATIONS
INTRODUCTION
This is Volume
2 of an introductory series on radio communications
Technology.
This volume covers very high frequency (VHF), ultra high
frequency
(UHF), and Satellite Communications (SATCOM) technologies,
as well as
the modern digital coding and modulation capabilities that optimize information
output and security.
The Communicator’s Tool Kit
A carpenter
relies upon an assortment of chisels, drills, and hammers to
do the job.
Each type of tool is suited for a particular task. Likewise, the modern
communications system designer makes use of HF, VHF, UHF, and
SATCOM tools,
and capitalizes on the unique capabilities that each brings
to meet the
requirements. Summaries of the most prominent capabilities
of each radio
frequency band are given below. Subsequent chapters will
describe
them in more detail.
HF: Around the Corner to Around the World
Before SATCOM
technology existed, HF radios were the only means of
communicating
to ships at sea. The fact that HF can communicate beyond
the horizon
makes it an indispensable tool for long distance ship- to- ship
and ship-to-shore
messages. Likewise, before the days of the transatlantic
cables, HF
(or short wave) radios were the only way to talk between
continents.
Today they are still used to share the overall burdens of
long distance
communications.
But the unique
virtue of HF radio has also created some challenges.
Worldwide
radio transmissions are easy to intercept and the HF spectrum
is complicated
by signals emanating from the many individual transmitters
located around
the world. Special techniques must be implemented in the
radios to
take advantage of the radio’s long range, while still preserving
the clarity
of the channel and reduce interception.
Encryption
reduces unfriendly utilization of intercepted signals and
sophisticated
coding schemes helps fight through clutter, but these
techniques
can reduce throughput (compared to that of a clear channel).
Nevertheless,
HF radios still play an indispensable role in the communicator’s tool kit.
HF manpack radios with various antenna options can cover a practical range
of from “around the corner” to “around the world.”
Although
some long range communications are now transmitted via satellite, HF still
has the advantage of not requiring (or relying on) any infrastructure.
VHF: Man to Man
The VHF band was an early choice for manpack radios used by ground troops to communicate within a local (five- mile or so) area. Antennas and selective- tuning components of VHF radios are very much smaller than their HF counterparts.
Advances in
the semiconductor industry have also increased the efficiency
of VHF radios
because batteries are smaller, lighter, and longer- lived than those required
in the past.
Unlike HF,
VHF transmissions lack the ability for ionospheric bounce and
are limited
to line- of- sight (LOS) communication. This reduces radio emission clutter
throughout an extended battlefield and limits the vulnerability to unfriendly
interception.
The wider
channel bandwidth capabilities of VHF radios increase the
efficiency
of coding and encryption schemes and allow greater data
throughput
than that of HF radios. Wider bandwidth and limited range make these radios
ideal for squad- to- squad communications.
UHF: Ground to Air for Close Support
UHF tuning elements and antennas are even smaller than those of VHF and are much easier to mount on supersonic fighter aircraft, making UHF an ideal choice for ground- to- air communications. Like VHF radios, UHF radios share the advantages of being line of sight and having wide bandwidth. Modern military forces now prefer the UHF spectrum for ground-to-air communications.
SATCOM: Hails to (and from) the Chief
It is essential for front line units to communicate with the command centers that are sometimes hundreds, if not thousands, of miles away. With the advent of military satellites, SATCOM technology can complement HF equipment.
Although LOS
is typically five miles or less along the ground between
manpack radios,
the vertical LOS range of a UHF signal is tens of
thousands
of miles. This enables UHF radios to reach orbiting military
satellites
that are designed to retransmit the signal back to earth. The
retransmitted
signal covers a huge footprint and is ideal for long range
communications.
The highly
directional antennas pointed up at the sky that are used with
Tactical
Satellite (TACSAT) radios, reduce ground radiation of front line
TACSAT traffic.
This makes SATCOM traffic much more difficult to
intercept
than that from HF radios.
Although it
is true that the enemy can receive a downlink from a satellite,
encryption
denies access to the data and the source of the emanations
gives no
clue as to the location of either the source or the destination
of the data
path.
The Multiband Radio
In this age
of specialization a large, conventional military force has the
ability to
carry an assortment of radios, each carefully designed for a
specific
purpose. But the situation of a small Special Forces combat team
is very different.
Although they need to have access to all of the available military communication
channels, they can’t afford the luxury (or the weight) of carrying the
required multitude of radios. Hence, the
multiband
radio.
Similarly, installation space constraints in vehicles, shelters, small boats, etc., are being addressed with multiband radios.
Just as the
small multipurpose pocket tool that folds open to display a
knife, screw
driver, pliers, and can opener can serve as an emergency tool
box, the
multiband manpack radio is designed for the multipurpose needs
of Special
Forces. Some multiband radios also provide a satellite link
allowing
them to extend their range further.
Putting it all together
Subsequent
chapters in this handbook develop the basic principles and
operating
modes of the radios mentioned in this introduction. Operating
characteristics
of each radio frequency band will be described and
compared
with respect to performance and application.
But there
is a lot more than frequency band that defines the performance
of a radio.
The following pages also touch upon the world of exotic
waveforms
that punch through noise, defy attempts at interception, and
provide data
high data rates that previously were considered impossible.
Stay tuned!