carr, j. j. (2001). antenna toolkit (2nd ed.)

Antenna Toolkit Antenna Toolkit 2nd Edition Joseph J. Carr, K4IPV Newnes OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Newnes An imprint of Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 1997 Reprinted 1998 Second edition 2001 ß Joseph J. Carr 1997, 2001 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Rd, London, England W1P 0LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 4947 X Typeset by Keyword Typesetting Services Ltd Printed in Great Britain by Preface vii 1. Radio signals on the move 1 2. Antenna basics 19 3. Wire, connection, grounds, and all that 49 4. Marconi and other unbalanced antennas 69 5. Doublets, dipoles, and other Hertzian antennas 87 6. Limited space antennas 118 7. Large loop antennas 129 8. Wire array antennas 153 9. Small loop antennas 176 10. Yagi beam antennas 195 11. Impedance matching 203 12. Simple antenna instrumentation and measurements 221 13. Getting a ‘good ground’ 237 Index 249 v Contents If you are interested in amateur radio, short-wave listening, scanner mon- itoring, or any other radio hobby, then you will probably need to know a few things about radio antennas. This book is intended for the radio enthu- siast – whether ham operator, listening hobbyist, or radio science obser- ver – who wants to build and use antennas for their particular requirements and location. All of the antennas in this book can be made from wire, even though it is possible to use other materials if you desire. These antennas have several advantages. One of the most attractive is that they can provide decent performance on the cheap. As one who has lived through the experience of being broke, I learned early to use bits of scrap wire to get on the air. My first novice antenna back in the late 1950s was a real patched-together job – but it worked really well (or so I thought at the time!). Another advantage of wire antennas is that they are usually quite easy to install. A couple of elevated supports (tree, roof, mast), a few meters of wire, a few bits of radio hardware, and you are in the business of putting up an antenna. As long as you select a safe location, then you should have little difficulty erecting that antenna. Finally, most high-frequency (HF) short-wave antennas are really easy to get working properly. One does not need to be a rocket scientist – or pro- fessional antenna rigger – to make most of these antennas perform as well as possible with only a little effort. There is quite a bit of detailed technical material to digest if you want to be a professional antenna engineer, but you can have good results if you follow a few simple guidelines. vii Preface SOFTWARE SUPPLEMENT TO THIS BOOK _________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ At the time this book was conceived it was noted that the technology now exists to make Microsoft Windows-based antenna software available to readers along with the book. The software can be used to calculate the dimensions of the elements of most of the antennas in this book, as well as a few that are not. There are also some graphics in the software that show you a little bit about antenna hardware, antenna construction, and the like. ANTENNA SAFETY _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Every time I write about antenna construction I talk a little bit about safety. The issue never seems too old or too stale. The reason is that there seem to be plenty of people out there who never get the word. Antenna erection does not have to be dangerous, but if you do it wrong it can be very hazardous. Antennas are deceptive because they are usually quite lightweight, and can easily be lifted. I have no trouble lifting my trap vertical and holding it aloft – on a windless day. But if even a little wind is blowing (and it almost always is), then the ‘sail area’ of the antenna makes it a lot ‘heavier’ (or so it seems). Always use a buddy-system when erecting antennas. I have a bad back caused by not following my own advice. Another issue is electrical safety. Do not ever, ever, ever toss an antenna wire over the power lines. Ever. Period. Also, whatever type of antenna you put up, make sure that it is in a location where it cannot possibly fall over and hit the power line. The last issue is to be careful when digging to lay down radials. You really do not want to hit water lines, sewer lines, buried electrical service lines, or gas lines. I even know of one property where a long-distance oil pipeline runs beneath the surface. If you do not know where these lines are, try to guess by looking at the locations of the meters on the street, and the service entrance at the house. Hint: most surveyers’ plans (those map-like papers you get at settlement) show the location of the buried services. They should also be on maps held by the local government (although you might have to go to two or three offices!. The utility companies can also help. A NOTE ABOUT UNITS AND PRACTICES ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ This book was written for an international readership, even though I am American. As a result, some of the material is written in terms of US standard practice. Wherever possible, I have included UK standard wire sizes and metric units. Metric units are not in common usage in the USA, but rather we still use the old English system of feet, yards, and inches. Although many Americans (including myself) wish the USA would convert to SI units, it is not likely in the near future. UK readers with a sense of viii ANTENNA TOOLKIT history might recognize why this might be true – as you may recall from the George III unpleasantness, Americans do not like foreign rulers, so it is not likely that our measuring rulers will be marked in centimeters rather than inches. * For those who have not yet mastered the intricacies of converting between the two systems: 1 inch ¼ 2:54 centimeters (cm) ¼ 25:4 millimeters (mm) 1 foot ¼ 30:48 cm ¼ 0:3048 meter (m) 1m ¼ 39:37 inches ¼ 3: 28 feet Joseph J. Carr PREFACE ix *I apologize for the bad play on words, but I could not help it. [...]... 18 ANTENNA TOOLKIT WATER CHAPTER 2 Antenna basics Before looking at the various antennas we need to look at some of the basics of antenna systems In this chapter you will learn some of these basics And while they will not make you a red-hot professional antenna engineer they will set you up well enough to understand this book and others on amateur and hobbyist antennas We will look at the matter of antenna. .. radiation, antenna patterns, the symbols used to represent antennas, voltage standing wave ratio (VSWR), impedance, and various methods suitable for constructing wire antennas in the high-frequency (HF) and very high-frequency (VHF) regions of the spectrum ANTENNA SYSTEM SYMBOLS _ Figures 2.1 and 2.2 show the various symbols used to represent antennas... in wireless communications: radio waves travel, as if by magic, from a transmitting antenna to a receiving antenna (Figure 2.3) Whether the two antennas are across the garden from each other, across continents and oceans, or on the Earth and the Moon, if there is not a transmitting antenna and at least one receiving antenna in the system then no communications can take place At one time, physicists... other) When the EM wave intercepts the receiver antenna, it sets up a copy of the original oscillating currents in the antenna, and these currents are what the receiver circuitry senses The orthogonal E- and H-fields are important to the antenna designer If you could look directly at an oncoming EM wave, you would see a plane front advancing from the transmitting antenna If you had some magical dye that would... increases, requiring ever more sensitive receivers and better antennas FIGURE 2.6 ANTENNA BASICS 23 _ _ THE ELECTROMAGNETIC WAVE The electromagnetic (EM) wave propagating in space is what we know as a ‘radio signal.’ The EM wave is launched when an electrical current oscillates in the transmitting antenna (Figure 2.7) Because moving electrical currents... partially upon the angle of radiation of the transmitting antenna A high angle of radiation causes a shorter skip zone, while a lower angle of radiation results in a longer skip zone Communication between any particular locations on any given frequency requires adjustment of the antenna radiation angle Some international short-wave stations have multiple antennas with different radiation angles to ensure... polarization would be horizontal One way to tell which polarization an antenna produces when it transmits, or is most sensitive to when it receives, is to note the direction of the radiator element If the radiator element is vertical, i.e perpendicular to the Earth’s surface, then it is vertically polarized But if FIGURE 2.7 24 ANTENNA TOOLKIT FIGURE 2.8 the radiator element is horizontal with respect... receiver antennas are shown, one is vertically polarized (VD) and the other is horizontally polarized (HD) In Figure 2.9A, the arriving signal is vertically polarized Because the E-field vectors lines are vertical, they cut across more of the VD antenna than the HD, producing a considerably larger signal level The opposite is seen in Figure 2.9B Here the E-field is horizontally polarized, so it is the HD antenna. .. designers tell us that a signal-to-noise ratio of 10 dB is necessary for ‘comfortable listening,’ while a signal-to-noise ratio of 3 dB is ANTENNA BASICS 25 TABLE 2.1 Ratio Power (dB) Voltage (dB) 1:1 2:1 1:2 10:1 1:10 0 þ3 À3 þ10 À10 0 þ6 À6 þ20 À20 FIGURE 2.9 26 ANTENNA TOOLKIT ... here to there, and the radio operator to get a transmission path from here to there The heading of a directional antenna is normally aimed at the receiving station along its great circle path Unfortunately, many people do not understand the concept well enough, for they typically aim the antenna in the wrong direction Radio waves do not travel along what appears to be the best route on a flat map Instead . Antenna Toolkit Antenna Toolkit 2nd Edition Joseph J. Carr, K4IPV Newnes OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Newnes An imprint of Butterworth-Heinemann Linacre House, Jordan. Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 1997 Reprinted 1998 Second edition 2001 ß Joseph J. Carr 1997, 2001 All rights reserved Hertzian antennas 87 6. Limited space antennas 118 7. Large loop antennas 129 8. Wire array antennas 153 9. Small loop antennas 176 10. Yagi beam antennas 195 11. Impedance matching 203 12. Simple antenna