Basic NEC with Broadcast Applications THE PURPOSE OF COMPUTING IS INSIGHT, NOT NUMBERS – R.W Hamming Basic NEC with Broadcast Applications J.L Smith, PE AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Focal Press is an imprint of Elsevier Acquisitions Editor: Angelina Ward Publishing Services Manager: George Morrison Project Manager: Marilyn E Rash Assistant Editor: Kathryn Spencer Marketing Manager: Christine Degon Veroulis Design Direction: Joanne Blank Cover Design: Gary Ragaglia Cover Images © J.L Smith Text Printer: Sheridan Books Cover Printer: Phoenix Color Corp Focal Press is an imprint of Elsevier 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA Linacre House, Jordan Hill, Oxford OX2 8DP, UK Copyright © 2008, Elsevier Inc All rights reserved No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (ϩ44) 1865 843830, fax: (ϩ44) 1865 853333, E-mail: permissions@elsevier.com You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting “Support & Contact” then “Copyright and Permission” and then “Obtaining Permissions.” Library of Congress Cataloging-in-Publication Data Smith, J.L Basic NEC with broadcast applications / J.L Smith p cm Includes index ISBN 978-0-240-81073-7 (alk paper) Antenna arrays Radio—Transmitters and transmission Transmitters and transmission I Title TK7871.6.S566 2008 621.384’135—dc22 2008004493 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library For information on all Focal Press publications visit our website at www.books.elsevier.com 08 09 10 11 12 54321 Printed in the United States of America To my lovely wife, Marguerite, who has been in my corner for 63 years She assures me that I’m the Champ, she tells me that I’m winning, and she pushes me back into the ring to fight another round This page intentionally left blank Contents Foreword Preface Acknowledgments About the Author CHAPTER 1.1 1.2 1.3 1.4 1.5 1.6 1.7 xiii xv xix xxi The Array Adjustment Process .1 The Nature of NEC-2 The Directional Antenna Adjusting Process .1 Local and Global Minima The Role of NEC-2 .4 Analysis Overview Additional NEC-2 Benefits Software Requirements CHAPTER NEC-2 Fundamentals 2.1 2.2 2.3 2.4 Scope The NEC-2 Engine NEC-2 Operation 11 Creating the Input File .11 2.4.1 Naming the Files 11 2.4.2 Data Commands 12 2.4.3 Data Command Types 13 2.4.4 An Input File Illustration .13 2.5 Reading the Output File 17 2.5.1 The Header 18 2.5.2 Structure Specifications 18 2.5.3 Segmentation Data 18 2.5.4 Data Commands, Frequency, Loading, and Environment Data 21 2.5.5 Antenna Input Parameters 22 2.5.6 Currents and Locations 22 2.5.7 Current Moments 23 2.5.8 Power Budget 24 2.5.9 Radiation Pattern 24 2.6 Exercises 26 CHAPTER Modeling the Radiator 27 3.1 Modeling Guidelines .27 3.2 Guideline Summary 29 vii viii Contents 3.2.1 Modeling the Radiator 29 3.2.2 Modeling the Voltage Source .29 3.3 Tower Configurations 30 3.3.1 Single-Wire Configuration .31 3.3.2 Four-Wire Configuration .31 3.3.3 Two-Wire Configuration 32 3.3.4 Lattice Configuration 32 3.4 Viewing Tower Configuration 38 3.5 Exercises 39 CHAPTER Array Geometry 41 4.1 4.2 4.3 4.4 The Coordinate System 41 Array Geometry: An Example 44 The Array Input File 46 Exercises 50 CHAPTER Loads, Networks, and Transmission Lines 51 5.1 Modeling Impedance Loads .51 5.2 Modeling Nonradiating Networks 53 5.2.1 Typical Networks 54 5.2.2 Typical Network Applications .55 5.2.3 General Guidelines for Networks 57 5.3 Modeling Transmission Lines 57 5.4 Network Output File Listing 59 5.4.1 Network Descriptions 59 5.4.2 Source and Load Impedance to the Networks 60 5.4.3 Network Input Parameters 61 5.5 Exercises 61 CHAPTER Calculating Base Drive Voltages .63 6.1 6.2 6.3 6.4 Base Drive Voltages 63 Direct and Induced Currents 63 Current Moments .66 Development Concept 67 6.4.1 Unity Drive 68 6.4.2 Normalized Drive 69 6.4.3 Full Power Drive 71 6.4.4 Shunt Reactance and Networks 71 6.5 Example: A Three-Tower Array 72 6.5.1 Create a Unity Drive File .72 6.5.2 Calculate Unity Drive Current Moments .73 Contents 6.5.3 Solve for the Normalized Drive Voltages .77 6.5.4 Determine the Full Power Drive Voltages .78 6.6 Exercises 79 CHAPTER Using Data from the Output File 81 7.1 7.2 7.3 7.4 Overview 81 Verify the Field Ratios 82 Plot Far-Field Radiation Pattern 83 Detuning Unused Towers 84 7.4.1 Detuning by Base Loading 85 7.4.2 Detuning by Skirting .89 7.5 Antenna Monitor Readings 94 7.5.1 Optimum Height for Sample Loops 95 7.5.2 Arbitrary Height for Sample Loops .96 7.5.3 Base Current Samples 97 7.5.4 Base Voltage Samples 99 7.6 Drive Point Impedance 100 7.6.1 Drive Point Impedance When Using a Network 100 7.7 Exercises 102 CHAPTER Model by Measurement .105 8.1 Objective 105 8.2 Adjusting the Model .107 8.2.1 Number of Segments 108 8.2.2 Tower Diameter 111 8.2.3 Segment and Radius Taper 114 8.2.4 Base Capacity 116 8.2.5 Drive Segment Radius 118 8.3 Exercise 120 CHAPTER Top-Loaded and Skirted Towers 121 9.1 General Considerations 121 9.2 Top Loading 122 9.2.1 Estimating the Size of the Top Hat 122 9.2.2 Determining the Degree of Top Loading 123 9.3 Skirted Towers .126 9.4 Folded Monopole 129 9.5 Exercises 132 ix Software arrays; therefore, it does not have the ability to model 120 radial ground screens It is important to know that the GM command as modified by bnec.exe is not compatible with the usual unmodified NEC2dxs programs The GM command is, however, compatible with the NEC-4 file format; therefore, the input files generated during the study of this book are, for the most part, usable with both bnec.exe and NEC-4 should the reader elect to get the license for NEC-4 When bnec.exe is run, it issues a call for the path and name of the input file plus the name that the user wishes to assign to the output file There are no other communications with the user while NEC-2 runs Bnec.exe stores its output in a file that it places in the computer’s currently active folder The user must recall the output file to read, print, or otherwise use it The output file is most conveniently viewed using WordPad A satisfactory hard copy of the output file can be printed in the portrait orientation by changing the font of the entire file to size The font can be changed to size if the file is printed in the landscape orientation 3.2 NVCOMP.EXE NVCOMP.EXE was created by Glenn Stumpff (gstumpff@yahoo.com) and at the time of this writing is contained in the software package designated as NVNEW.ZIP on the Internet at http://www.si-list.net/ swindex.html The package contains an enhanced version of David de Schweinitz’s NV program These enhancements include support for GA, GH, GM, GX, and GR commands as well as support for VGA graphics It has the capability to output a PCX or BMP image file to the current folder and it also works with NEC-4 input files Assuming that NVCOMP.EXE is included in the PATH variable and the NEC-2 input file to be viewed is in the current folder, then to use the program it is only necessary to type NVCOMP followed by the name of the NEC-2 input file to be viewed An image of the array will appear on the screen with control guides listed on the right screen 263 264 Appendix C edge The control guides are explained as follows in the order of probable use SHIFT AXIS – Pressing moves the total image down Pressing moves the image left Pressing moves the image right Pressing moves the image up Pressing returns the image to the origin CHANGE SCALE – Pressing Page Up zooms out Pressing Page Down zooms in ROTATE IMAGE – The arrow keys rotate the image.The current angles are displayed under the headings PHI and THETA HIGHLIGHT WIRE – When the image is first displayed, wire is highlighted.The highlighted wire can be changed pressing ϩ or Ϫ on the numerical keypad WIRE PARAMETERS – The parameters of the highlighted wire are displayed along the bottom of the screen.The wire number is listed along with its tag, segment, end coordinates, end coordinates, and wire radius CHANGE COLOR – Pressing various keys cycles colors of the image through a fixed color set Pressing B changes background color Pressing L changes line colors Pressing S changes the color of the highlighted wire Pressing X, Y, or Z changes the color of the X-, Y-, or Z-axis To make an axis invisible, give it the same color as the background NVCOMP.EXE has the capability to save an image in a file using either the PCX or BMP image formats If VGA mode 12 is in use, a PCX file of the displayed NEC-2 geometry will be written in the current folder when “C” (or “c”) is pressed The file will be given the default name NECGEO.PCX This capability is currently only available Software if NVCOMP succeeds in autodetecting video mode 12 (If you don’t see the “C FOR PCX” instruction on the lower right screen, the option isn’t available because the computer is not in mode 12.) NVCOMP will create a BMP file of the displayed NEC-2 geometry when “T” (or “t”) is pressed The file will be given the default name NEC00000.BMP if you press “T” once since first running NVCOMP If you press “T” a second time, the file will be given the default name NEC00001.BMP, and then NEC00002.BMP if you press “T” again, and so on As before, this capability is only available if NVCOMP succeeds in autodetecting video mode 12 Also, if you don’t see the “C FOR PCX” and “T for BMP” instruction on the lower right side of the screen, the option isn’t available because the computer is not in mode 12 The primary purpose of having differently named BMP files with every press of “T” is for use of this output feature with the capability of NVCOMP to display multiple geometries stored in a single NEC-2 file 3.3 NecDrv2.EXE NecDrv2.EXE is a postprocessing program written by the author to read a NEC-2 unity drive output file (CALL_1.OUT) and process the data to calculate the base drive voltages that will create a specified set of field ratios It is important to remember that this program (and most other postprocessing programs written by the author) expects the wires to be identified using the standard notation defined in the text The wires are identified using three-digit numbers with the first digit denoting the tower number and the remaining two digits denoting the wire number on that particular tower, for example, wire on tower is identified as 203 The use of NecDrv2.EXE is quite intuitive Assuming it is included in the PATH variable, the program is called from the folder containing the file CALL_1.OUT by typing “NecDrv2” and pressing ϽENTERϾ An input screen appears where the user is asked to identify the subject output file The file is identified by typing “CALL_1.OUT” in the given box then clicking Enter A set of boxes appears into which the user must enter the desired field ratio and phase for each tower then click Continue If the correct 265 266 Appendix C notation has not been used to identify the towers and wires, then the correct number of boxes may not appear Once the input data has been entered, NecDrv2.EXE displays a set of boxes containing the normalized base drive voltages that will create the desired field ratios These drive voltages are displayed in their Real and Imaginary format When used in a bnec.exe run, they will yield the correct pattern shape but not the correct pattern size The normalized voltages must be scaled upward, as described in the text to create the correct pattern size The output screen also provides the option for a hardcopy printout of the results It gives the choice of printing the principal and induced moments plus the normalized drive voltages, or printing just the normalized drive voltages 3.4 NECMOM.EXE NECMOM.EXE is a postprocessing program written by the author to read a NEC-2 output file (either CALL_N.OUT or CALL.OUT) and calculate both the current moment of each tower, and the field ratios created by the drive voltages used to generate the output file This is useful to confirm the validity of a calculated set of drive voltages or in any other instance in which it is desired to view the actual current moments The program is called in the usual way by typing “NECMOM” from the folder containing the target output file (either CALL_N.OUT or CALL.OUT) The screen asks for the target file identity then ϽENTERϾ No other effort by the user is required NECMOM.EXE prints an output screen showing the drive voltages used, the calculated current moments and the calculated field ratios The user has the option to obtain a hardcopy printout of the moments and field ratios 3.5 WJGRAPS.EXE The WJGRAPS.EXE program is a free public domain program that, at the time of this writing, is available for download from http://www.si-list net/swindex.html under the heading IGRAPS It reads a NEC-2 output Software file and makes a rather simplified plot of the radiated pattern as generated by the RP command in the NEC-2 input file.VBRUN200.DLL is a run time file that must be in the same folder as WJGRAPS.EXE or on a path such that the run time file can be located when WJGRAPS.EXE runs When the program is called by typing “WJGRAPS ϽENTERϾ”, a blank screen appears with a short header at the top giving the choices “File”,“Print”, and “Exit” When File is clicked, an Open box drops down and when Open is clicked, a dialog box opens showing all files in the current folder Highlight the desired file and click OK to create the pattern on the screen Clicking Print on the header creates a hard copy of the pattern using the default printer Clicking Exit terminates the program Although there are no markings on the graph, it is useful to know that the pattern is normalized to its maximum value and that there are ten rings Consequently, each ring is 10 percent of the maximum value Angular markings appear at 10-degree intervals so a little ingenuity allows the reader to get some idea of the numerical details of the pattern 4.1 Software Support The software on the CD included with this book is furnished without charge as a convenience to the reader.The author is not able to provide technical support of any kind No warranty is provided as to the accuracy or capability of the software and neither the author nor the publisher assumes responsibility for the results of its use (See also Warranty on the envelope of the CD included with this book.) 267 This page intentionally left blank Index A Alpha angle, 18–19 ANTENNA ENVIRONMENT, 183 ANTENNA INPUT PARAMETERS, 61, 98 drive point impedances in, 100–102 antenna input parameters, 22, 23 antenna monitor readings, 94–100 base current samples, 97–99 base voltage samples, 99–100 height for sample loops, 96–97 optimum height for sample loops in, 95–96 six-tower array, day pattern, 155–156 six-tower array, night pattern, 160, 161, 162 tall-tower array, 167 three-tower array, 151 antenna-tuning units (ATUs) drive voltages, 140–141 impedance of, 138–139 input impedances, 142 tower base impedances, 141–142 transmission line impedances, 143–144 array adjustment, 1–7 directional, 1–2 local and global minima in, 2–4 mathematical synthesis in, nature of NEC-2 and, physical, role of NEC-2 in, array geometry, 41–50 array input file for, 46–49 coordinate system in, 41–44 example of, 44–46 ATUs See antenna-tuning units AUTOEXEC.BAT file, 17 azimuth angle, 24–25 displacement, 41 six-tower array, night pattern, 164 B bandwidth analysis, 133–148 base drive voltages, 63–80 in antenna monitor readings, 99–100 current moments and, 66–67, 73–77 direct and induced current, 63–65 drive point impedance and, 101 example of, 72–79 field ratio calculation and, 67–72 full power drive, 71, 78–79 normalized drive, 69–71, 77–78 shunt reactance and, 71–72 source impedance of, 137–140 in system bandwidth analysis, 136, 137–140 tall-tower array, 167, 168 unity drive, 68–69, 72–77 base insulators, 107 capacity of, 116–118 drive segment radius and, 118–120 modeling by measurement, 116–118 in system bandwidth analysis, 135–136 base loading detuning by, 85–88 skirting with, 92–93 269 270 Index Beta angle, 18–19 bnec.exe, 260, 262–263 reading, 17–25 Burke, G J., xiii–xiv, xv, 9–10 buss voltage, 144–145 C CALL_1.NEC, 68–69 CALL.NEC file running, 17 CALL_N.NEC, 71 CALL_N.OUT, 71, 266 CALL.OUT, 81, 266 See also output files CALL_1.OUT, 68 Carlier, P., xix carrier frequency, 134 case studies, 149–169 six-tower array, day pattern, 154–159 six-tower array, night pattern, 160–165 tall-tower array, 166–169 three-tower array, 149–154 CE command input file, 14, 188 NX and, 174, 176 circular polarization, clip lead resistance, 107–108 CM command input file, 14, 188 NX and, 174 commands See also individual commands comment, 187–188 program control, 13, 16–17, 212–250 structure geometry command, 189–210 comment commands, 13, 14, 187–188 CE, 14, 174, 176, 188 CM, 14, 188174 common point-matching networks, 146 compass headings, 42, 43–44 “Computer Analysis of the Bottom-fed Fan Antenna” (Burke and Poggio), 171 connection data, 19–20 coordinate planes, reflection in, 205–208 coordinate transformation, 195–196 coupling calculation, 212 CP command, 212 Cram, P., xix current in antenna monitor readings, 97–99 base voltage and, 67–68 direct, 63–65 distribution, listing, 6, 95–96 field ratios and, 82 induced, 63–65 and location output file, 22–23 phase shift, 140–141 sinusoidal distribution of, 66 top loading, 122–126 current moments, 23–24 base drive voltage and, 66–67 base voltage and, 67–68 field ratios and, 82 unity drive, calculating, 73–77 cylindrical structures, generating, 198–200 D data command, 12–13 delimiting, 12 output file, 21–22 types of, 13 data storage for plotting, 128, 238–239 detuning towers, 84–94 by base loading, 85–88 by skirting, 89–94 Index directional antenna adjustment, 1–2 drive point impedance, 100–102 bandwidth analysis and, 138–139 base capacity and, 117–118 modeling by measurement, 105–120 six-tower array, day pattern, 156 six-tower array, night pattern, 161–164 tall-tower array, 168 three-tower array, 152–153 tower diameter and, 111–114 drive segment radius, 118–120 drive signal simulation, 148 drive splitting, 171–173 drive voltage, 47–48 dummy wires, 101 E EK command, 213 in modeling by measurement, 109 elevation angle, 41, 42, 43 elliptical polarization, EN command, 214 end geometry input, 191–192 end of run command, 214 environment data, 21–22 error messages, 251–258 errors, input file, 17 excitation command See EX command EX command, 16, 211, 215–218 in network modeling, 56–57 voltage source modeling with, 29–30, 137 execute command, 211, 249–250 extended thin-wire kernel approximation, 213 F far-field pattern listings, 81 far-field radiation patterns, plotting, 83–84 field ratios in detuning by skirting, 91–92 local and global minima and, 2–3 six-tower array, night pattern, 164 verifying, 82 finite grounds, 9, 181–183 FLMO.NEC, 130–131 folded monopole towers, 32, 129–131 four-wire configurations, 31–32 FR command, 16, 211, 219–220 in bandwidth analysis, 137 frequency in bandwidth analysis, 137 FR command, 16, 211, 219–220 program control command and, 21–22 full power drives, 71 voltage calculation, 78–79 G GA command, 190 GC command, 202–204 segment and radius taper and, 114–116 in system bandwidth analysis, 136 GD command, 221–222 GE command, 191–192 input file, 15–16 NX and, 176 geometry command, 13 input file, 14–16 geometry print control, 197 GF command, 193 GH command, 194 global minima, 2–4 GM command, 11, 195–196 in detuning by skirting, 90, 93–94 folded monopoles and, 130–131 NX and, 176 in radiator modeling, 38 stacking sections with, 32, 36–37, 38 271 272 Index GN command, 177–178, 223–225 input file, 16 GP command, 197 GR command, 178–181, 198–200 NX and, 176 grounding straps, 34–35 ground parameters, 177–178, 223–225 additional, 221–222 grounds, finite, 9, 181–183 ground screens, 28, 177–181 GS command, 201 NX and, 176 GW command, 202–204 array geometry with, 46, 47 in detuning by skirting, 93–94 drive wire definition with, 33–34 input file, 14–15 in network modeling, 56 in system bandwidth analysis, 136 GX command, 205–208 NX and, 176 H Hatfield, J B., 106–107 height adjustment, 35 array geometry for, 44 optimum height for antenna monitor reading sample loops, 95–96 for sample loops in antenna monitor readings, 96–97 helix and spiral specification, 194 helix structures, I IEEE Transactions on Broadcasting (Trueman), 63, 133 impedance See also drive point impedances ATU input, 142 base capacity and, 116–118 calculating intermediate data on, 140–141 drive point, 100–102 drive segment radius and, 118–120 load, 51–53, 60–61 matching, 53 modeling by measurement, 105–120 parallel feeds and, 171–173 in parallel in networks, 56 phasing network input, 143, 145 power divider input, 143, 145 segment number vs., 108–109 self-, 149–151, 154–155, 160, 166, 171–172 series, 55–56, 57 shunt, 57 source, 60–61, 137–140 tall-tower array, 167 taper and, 114–116 thin vs thick wire, 109–110 tower base, 141–142 tower diameter and, 111–114 transmission line input, 143–144 in transmission line modeling, 58 inductance in detuning by base loading, 85–86 in LD command, 52 in modeling by measurement, 107 test lead, 107–108 input files array, 46–49 base loading, 88 command for, 185–250 comment command, 187–188 creating, 11–17 data command with, 12–13 detuning by skirting, 93–94 illustration of, 13–17 naming, 11–12 normalized drive, Index six-tower array, day pattern, 158–159 six-tower array, night pattern, 165 structure geometry command, 189–210 tall-tower array, 168, 169 three-tower array, 153–154 unity drive, interaction approximation range, 226 K KH command, 226 L lattice configurations, 32–38 coding, 33–37 current distribution in, 121 parallel feeds in, 171–173 simplified, 37–38 skirted, 121, 126–128 in system bandwidth analysis, 134–135 top-loaded, 121–126 Lawrence Livermore National Laboratories, xv, 9–10 LD command, 227–229 array geometry and, 48 in detuning by skirting, 93 floating-point numbers in, 52 in impedance load modeling, 51–53 NX and, 176 load modeling, 227–229 See also LD command impedance, 51–53 program control command and, 21–22 shunt impedance, 53 voltage source and, 57, 58 local minima, 2–4 loss modeling, 48 M mathematical synthesis, in array adjustment, measurement, modeling by, 105–120 adjustments in, 107–120 base capacity in, 116–118 drive segment radius in, 118–120 objectives of, 105–107 radius taper in, 114–116 segment length in, 114–116 segment number in, 107, 108–111 tower diameter in, 111–114 modeling rules, 178–179 monopoles folded, 32, 129–131 ground screens and, 179–180 Morecroft, J H., 31 N Naval Ocean Systems Center Technical Document 116 (TD 116), 185 near fields, 230–232 NecDrv2.EXE, 77–78, 260, 265–266 NEC2ds.zip, 262–263 NEC2dxs.xip files, 10 NECMOM.EXE, 181, 260, 266 NEC-2 (Numerical Electromagnetics Code version 2), xv, 5–6 benefits of, 6–7 case studies, 149–169 development of, 9–10 nature of, operation of, 11 public domain software with, role of in array adjustment, scope of, software requirements, software with, 259–266 user-friendliness of, xv 273 274 Index NEC-4 (Numerical Electromagnetics Code version 4), 10 NE command, 230–232 current computation with, 211 network modeling See also NT command common applications and, 55–57 common configurations, 53–55 common point-matching, 146 descriptions in, 59–60 drive point impedances in, 100–102 guidelines for, 57 input parameters in, 61 nonradiating, 53–57 NT command, 233–235 output files in, 59–61 parallel feeds in, 56, 171–173 phasing input impedances in, 144, 145 shunt reactance and, 71–72 source and load impedance in, 60–61 voltage transmission between networks in, 140–141 network phase, 53, 140–141 networks drive splitting in, 171–173 next structure command, 173–177, 236 NGF files See also Numerical Green’s Function reading, 193 writing, 248 NH command, 230–232 current computation with, 211 normalized drives, 69–71 voltage calculation, 77–78 NT command, 233–235 in bandwidth analysis, 137 in load modeling, 52 in network modeling, 57 in nonradiating network modeling, 53 NX and, 176 Numerical Electromagnetic Code (NEC) - Method of Moments, Part III: User’s Guide, 185 Numerical Green’s Function, 9, 175–177 NVCOMP.EXE, 38–39, 260, 263–265 detuning by base loading and, 90–91 folded monopoles in, 131 skirted towers in, 128–129 top loading in, 124–125 NV.EXE, 38 NX command, 173–174, 236 CE and, 176 Numerical Green’s Function and, 175–177 O output files, 5, 81–103 antenna input parameters in, 22, 23 antenna monitor readings in, 94–100 condensed, 81 current moments in, 23–24 currents and locations in, 22–23 data command with, 21–22 detuning towers with, 84–94 drive point impedances, 100–102 far-field radiation patterns and, 83–84 field ratio verification in, 82 header in, 18 network, 59–61 power budget in, 24, 25 radiation patterns in, 24–25 reading, 17–25 segmentation data in, 18–21, 81 skirted towers, 128–129 structure specifications for, 18, 19 Index P parallel feeds, 56, 171–173 parasitic radiation, comparisons for, 174 pass-through networks, 55 peak values, 22, 23 phase local and global minima and, 2–3 network, 53, 140–141 phasing network input impedance, 143, 145 shift, 140–141 phasing networks, 53 phi angle, 24–25 Pi-networks, 57 PL command, 238–239 vertical radiation patterns and, 128 plotting, 128, 238–239 Poggio, A M., xv, 9–10 power budget, 24, 25, 71 full power drive, 78–79 power divider input impedances, 143, 145 PQ command, 237 Principles of Radio Communication (Morecroft), 31 print control, 237, 240–241 program control command, 13, 16–17, 212–250 PT command, 240–241 R radiation patterns, 24–25, 242–245 See also RP command bandwidth, 146–147 detuning unused towers and, 84–94 folded monopole, 129–131 parasitic, 157–158, 162–163, 174 six-tower array, day pattern, 157–158 six-tower array, night pattern, 162–164 skirted towers, 121, 126–128 WJGRAPS.EXE for, 266–267 radiator modeling, 27–39 in lattice configurations, 35 tower configurations, 30–39 voltage source in, 29–30 radius taper, 114–116 reactance physical shunting, 98–99 shunt, 71–72, 107 Reflection Coefficient Approximation (RCA), 182 reflection in coordinate planes, 205–207 ring girth, 37 coding, 34 defining, 33 top loading and, 124 RP See radiation patterns RP command, 16–17, 242–245 array geometry and, 48 current computation with, 211 in plotting far-field radiation patterns, 83–84 S scaling structure dimensions, 201–204 segmentation data, 81 segment lengths intersection angle of, 28 load and, 52 in output files, 22–23 print control for charge on, 237 radiator modeling, 27–28, 29 radius taper and, 114–116 in system bandwidth analysis, 136 thick wire vs thin wire, 108–110 underground, 178–179 segment numbers, in modeling by measurement, 107, 108–111 275 276 Index self-impedance parallel feeds and, 171–172 six-tower array, day pattern, 154–155 six-tower array, night pattern, 160 tall-tower array, 166 three-tower array, 149–151 Sellmeyer, J., 149, 154, 160 shunt admittances, 59 shunt reactance, 71–72 in modeling by measurement, 107 single-wire configurations, 31 six-tower arrays day pattern, 154–159 night pattern, 160–165 skirted towers, 32, 121, 126–131 base loading and, 92–93 detuning with, 89–94 folded monopoles and, 129–131 SM command, 210 software, 259–267 installation of, 260–262 Sommerfeld/Norton finite-ground method, 9, 182–183 SP command, 9, 208–209 spider girth, 35, 37 defining, 33 top loading and, 124 spiral specification, 194 SQR.OUT base current samples and, 97–99 drive point impedances in, 100–102 in plotting far-field radiation patterns, 83–84 SQR_1.OUT, 73 STRUCTURE EXCITATION DATA AT NETWORK CONNECTION POINTS, 60–61 structure geometry command, 189–210 “A Study of AM Tower Base Impedance” (Hatfield), 106–107 Stumpff, G., 38 surface patches, 9, 208–209 multiple, 210 system bandwidth analysis, 133–148 base drive voltages in, 136, 137–140 common point-matching networks, 146 drive signal simulation in, 148 intermediate data in, 140–146 low-impedance towers and, 148 parameter smoothing in, 148 radiation bandwidth, 146–147 system definition for, 133–136 total system data in, 146–147 transmission lines in, 148 T tall-tower arrays, 166–169 templates, array input file, 48–49 TD 116, 185 TEMP.NEC, 49 test lead inductance, 107–108 text editing, 17 theta angle, 24–25, 42 three-tower arrays, 149–154 TL command, 57–59, 246–247 in bandwidth analysis, 134, 137 TL.NEC, 124 T-networks, 57, 101 top loading, 32 determining degree of, 123–126 top hat size estimation in, 122–123 tower base impedances, 141–142 tower configurations, 30–38 drive segment radius, 118–120 flexibility in modeling, 109 folded monopole, 129–131 four-wire, 31–32 lattice, 30, 32–38 new structure creation, 173–177 NX command for, 173–174 Index single-wire, 31 skirted, 121, 126–131 in system bandwidth analysis, 134–136 thick-wire, 30 three-tower, 149–154 top-loaded, 121–126 tower diameter in, 111–114 triangular, 30 two-wire, 32 viewing, 38–39 tower feeds, 53 transmission line modeling, 57–59, 246–247 frequency vs carrier frequency and, 148 input impedances, 143–145 in system bandwidth analysis, 134, 137 Trueman, C W., 63 twotwr.nec, 181 two-wire configurations, 32 U unity drives, 68–69 creating files for, 72–73 current moment calculation, 73–77 unity excitation, 68 V voltage modeling, 16–17 antenna monitor readings and, 99–100 array geometry and, 47–48 base drive, 63–80 buss, 144–145 driving point, calculating, 72–79 full power, 78–79 load, network, and source of, 57, 58 normalized drive, 77–78 source, 29–30 voltage sources, 52 impedance of drive voltage and, 137–140 W WG command, 248 wire arc specification, 190 wire radius, 28, 29 wire specification, 202–204 wire structure modeling, 10 WJGRAPS.EXE, 260, 266–267 WordPad, 81 X XQ command, 211, 249–250 277 .. .Basic NEC with Broadcast Applications THE PURPOSE OF COMPUTING IS INSIGHT, NOT NUMBERS – R.W Hamming Basic NEC with Broadcast Applications J.L Smith, PE AMSTERDAM... approximately 100 per year Basic NEC with Broadcast Applications was written to show how the features of NEC- 2 can be accommodated in the design and analysis of MF broadcast directional antennas... before the development of computer modeling In Basic NEC with Broadcast Applications, he describes methods he has developed to use the public domain NEC- 2 modeling code to design and tune MF directional