Antenna Toolkit - N5DUX

1 AntennaToolkitAntennaToolkit2ndEditionJo seph J. Carr, K4 IPVN ewnesOXFORDAUCKLANDBOSTONJOHANNESBURGMEL BOURNENEWDELHIN ewnesAn imprint o fButterworth-HeinemannLinacre House, Jordan Hill, Oxford OX2 8DP225 Wildwood Avenue, Woburn, MA 01801-2041A division o fReed Educational and Pro fessional Publishing LtdA member o fthe Reed Elsevier plc groupFirst published 1997 Reprinted 1998 Second edition 2001 Joseph J. Carr 1997, 2001 All rights reserved. No part o fthis publicationmay be reproduced in any material form (includingphotocopying or storing in any medium by electronicmeans and whether or not transiently or incidentallyto some other use o fthis publication) without thewritten permission o fthe copyright holder exceptin accordance with the provisions o fthe Copyright,Designs and Patents Act 1988 or under the terms o falicence issued by the Copyright Licensing Agency Ltd,90 Tottenham Court Rd, London, England W1P for the copyright holder s written permissionto reproduce any part o fthis publication should be addressedto the catalogue record for this book is available from the British LibraryISBN 0 7506 4947 XTypeset by Keyword Typesetting Services LtdPrinted in Great Britain byPrefacevii1.

2 Radio signals on the move 12. Antenna basics 193. Wire, connection, grounds, and all that 494. Marconi and other unbalanced antennas 695. Doublets, dipoles, and other Hertzian antennas 876. Limited space antennas 1187. Large loop antennas 1298. Wire array antennas 1539. Small loop antennas 17610. Yagi beam antennas 19511. Impedance matching 20312. Simple Antenna instrumentation and measurements 22113. Getting a good ground 237 Index249vContentsI fyou are interested in amateur radio, short-wave listening, scanner mon-itoring, or any other radio hobby, then you will probably need to know afew 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 particularrequirements and location. All o fthe antennas in this book can be madefrom wire, even though it is possible to use other materials if you antennas have several advantages.

3 One o fthe most attractive isthat they can provide decent performance on the cheap. As one who haslived through the experience o fbeing broke, I learned early to use bits o fscrap wire to get on the air. My first novice Antenna back in the late 1950swas a real patched-together job but it worked really well (or so I thoughtat the time!).Another advantage o fwire antennas is that they are usually quite easy toinstall. A couple of elevated supports (tree, roof, mast), a few meters of wire,a few bits o fradio hardware, and you are in the business o fputting up anantenna. As long as you select a safe location, then you should have littledifficulty erecting that , most high-frequency (HF) short-wave antennas are really easy toget working properly. One does not need to be a rocket scientist or pro-fessional Antenna rigger to make most of these antennas perform as wellas possible with only a little effort. There is quite a bit of detailed technicalmaterial to digest i fyou want to be a pro fessional Antenna engineer, but youcan have good results if you follow a few simple SUPPLEMENT TO THIS BOOK_____At the time this book was conceived it was noted that the technology nowexists to make Microsoft Windows-based Antenna software available toreaders along with the book.

4 The software can be used to calculate thedimensions o fthe elements o fmost o fthe antennas in this book, as wellas a few that are not. There are also some graphics in the software that showyou a little bit about Antenna hardware, Antenna construction, and the SAFETY_____Every time I write about Antenna construction I talk a little bit about issue never seems too old or too stale. The reason is that there seem tobe plenty o fpeople out there who never get the word. Antenna erection doesnot have to be dangerous, but i fyou do it wrong it can be very are deceptive because they are usually quite lightweight, and caneasily be lifted. I have no trouble lifting my trap vertical and holding italoft on a windless day. But if even a little wind is blowing (and it almostalways is), then the sail area o fthe Antenna makes it a lot heavier (or so itseems). Always use a buddy-system when erecting antennas. I have a badback caused by not following my own issue is electrical safety.

5 Do not ever, ever, ever toss an antennawire over the power lines. Ever. Period. Also, whatever type o fantenna youput up, make sure that it is in a location where it cannot possibly fall overand hit the power last issue is to be careful when digging to lay down radials. Youreally do not want to hit water lines, sewer lines, buried electrical servicelines, or gas lines. I even know o fone property where a long-distance oilpipeline runs beneath the surface. If you do not know where these lines are,try to guess by looking at the locations o fthe meters on the street, and theservice entrance at the house. Hint: most surveyers plans (those map-likepapers you get at settlement) show the location o fthe buried services. Theyshould also be on maps held by the local government (although you mighthave to go to two or three offices!. The utility companies can also NOTE ABOUT UNITS AND PRACTICES_____This book was written for an international readership, even though I amAmerican. As a result, some o fthe material is written in terms o fUSstandard practice.)

6 Wherever possible, I have included UK standard wiresizes and metric units. Metric units are not in common usage in the USA,but rather we still use the old English system o f feet, yards, and many Americans (including myself) wish the USA would convertto SI units, it is not likely in the near future. UK readers with a sense ofviiiANTENNATOOLKIT history might recognize why this might be true as you may recall from theGeorge III unpleasantness, Americans do not like foreign rulers, so it is notlikely that our measuring rulers will be marked in centimeters rather thaninches.*For those who have not yet mastered the intricacies o fconvertingbetween the two systems:1 inch 2:54 centimeters (cm) 25:4 millimeters (mm)1 foot 30:48 cm 0:3048 meter (m)1m 39:37 inches 3:28 *I apologize for the bad play on words, but I could not help who does any listening to radio receivers at all whether as a hamoperator, a short-wave listener, or scanner enthusiast notices ratherquickly that radio signal propagation varies with time and something mys-terious usually called conditions.

7 The rules of radio signal propagation arewell known (the general outlines were understood in the late 1920s), andsome predictions can be made (at least in general terms). Listen to almostany band, and propagation changes can be seen. Today, one can find pro-pagation predictions in radio magazines, or make them yourself using any ofseveral computer programs offered in radio magazine advertisements. Twovery popular programs are any of several versions of IONCAP, and aMicrosoft Windows program written by the Voice of America engineeringstaff called odd things occur on the air. For example, one of my favorite localAM broadcast stations broadcasts on 630 kHz. During the day, I get inter-ference-free reception. But after the Sun goes down, the situation changesradically. Even though the station transmits the same power level, it fadesinto the background din as stations to the west and south of us start skip-ping into my area. The desired station still operates at the same power level,but is barely audible even though it is only 20 miles (30 km) easily seen example is the 3 30 MHz short-wave bands.

8 Indeed,even those bands behave very differently from one another. The lower-frequency bands are basically ground wave bands during the day, andbecome long-distance sky wave bands at night (similar to the AM broad-cast band (BCB)). Higher short-wave bands act just the opposite: during theCHAPTER 1 Radiosignalsonthemove1day they are long-distance skip bands, but some time after sunset, becomeground wave bands very high-frequency/ultra high-frequency (VHF/UHF) scannerbands are somewhat more consistent than the lower-frequency even in those bands sporadic-E skip, meteor scatter, and a numberof other phenomena cause propagation anomalies. In the scanner bandsthere are summer and winter differences in heavily vegetated regions thatare attributed to the absorptive properties of the foliage. I believe I experi-enced that phenomenon using my 2 m ham radio rig in the simplex mode(repeater operation can obscure the effect due to Antenna and locationheight).THE EARTH S ATMOSPHERE_____Electromagnetic waves do not need an atmosphere in order to propagate, asyou will undoubtedly realize from the fact that space vehicles can transmitradio signals back to Earth in a near vacuum.

9 But when a radio wave doespropagate in the Earth s atmosphere, it interacts with the atmosphere, andits path of propagation is altered. A number of factors affect the interaction,but it is possible to break the atmosphere into several different regionsaccording to their respective effects on radio atmosphere, which consists largely of oxygen (O2) and nitrogen (N2)gases, is broken into three major zones: thetroposphere,stratosphere, andionosphere(Figure ). The boundaries between these regions are not verywell defined, and change both diurnally ( over the course of a day) troposphere occupies the space between the Earth s surface and analtitude of 6 11 km. The temperature of the air in the troposphere varieswith altitude, becoming considerably lower at high altitude compared withground temperature. For example, a 108C surface temperature couldreduce to 558C at the upper edges of the stratosphere begins at the upper boundary of the troposphere(6 11 km), and extends up to the ionosphere ( 50 km).

10 The stratosphereis called anisothermal regionbecause the temperature in this region is rela-tively constant despite altitude ionosphere begins at an altitude of about 50 km and extends up to500 km or so. The ionosphere is a region of very thin atmosphere. Cosmicrays, electromagnetic radiation of various types (including ultraviolet lightfrom the Sun), and atomic particle radiation from space (most of it from theSun), has sufficient energy to strip electrons away from the gas molecules ofthe atmosphere. The O2and N2molecules that lost electrons are calledpositive ions. Because the density of the air is so low at those altitudes, theions and electrons can travel long distances before neutralizing each other2 ANTENNATOOLKITby recombining. Radio propagation on some bands varies markedlybetween daytime and night-time because the Sun keeps the level of ioniza-tion high during daylight hours, but the ionization begins to fall off rapidlyafter sunset, altering the radio propagation characteristics after dark.