The great tragedy of Science - the slaying of a beautiful hypothesis by an ugly fact.
—Thomas H. Huxley (1825 - 1895)

INTRODUCTION

hen we think of software for use with the general field of antennas, we usually start—and end—with thoughts about antenna modeling software, namely, NEC and MININEC. These programs, along with a host of proprietary hybrid programs, represent some of the most complex software packages to which the user has access in a way that does not have too steep a learning curve to master. As well, they have some of the most extensive set of aids in the form of tutorials and continuing support. The “antenna modeling” column that runs monthly in antenneX is one example of the support available.

Like all software, NEC and MININEC have their limits. The limits come in two flavors. One type of limit rests on the algorithms used to calculate various antenna properties. These equations are simplifications of larger or more complete equations, and very often the form usable by the programming language does not permit direct inclusion of the most fundamental equation formulation. The second type of limitation has to do with premises that underlie the program. For example, both NEC and MININEC begin with straight round wires surrounded by a medium. Hence, their use in contexts that require non-round wires in a variable set of media is dubious. All software has limitations, and the user must be as aware of them as he is of how to use the software to obtain reasonable results. This principle applies not only to NEC, but also to all other software available to ease the process of design.

SO MANY CHOICES NOW
In addition to such seemingly cohesive design and analysis programs as NEC and MININEC (and their commercial and free implementations), the antenna experimenter has access to a vast collection of other software programs. The programs cover a large territory, from the calculation of transmission-line properties and networks between the antenna and the transmitting/receiving equipment to the calculation of ionospheric properties between sending and receiving stations. In the former category, we find TLW, the ARRL stand-alone program and TLD, AC6LA’s equally stand-alone program. Both programs are compact and highly competent at what they do. However, because each programmer has chosen a slightly different method of implementing the required equations for lossy lines and the method for the user to specify loss factors in a transmission line, the two programs may on occasion yield slightly different numerical results. This is another factor of which a user must be aware.

At the other end of the communications train are propagation programs, such as Proplab and ACE-HF PRO (the latter available from antenneX). Such programs usually use the VOACAP engine for calculations, although those who implement the core have embellished its functions. The user may begin with reasonably accurate models of his antenna(s) to tailor the calculations to his transmitting and receiving environment. Indeed, the programs are so extensive that we may use them equally to predict conditions for a given path at a given time of day for practical communications work or to make detailed studies of the many factors that affect propagation in the upper MF, the entire HF, and the lower VHF range on which the condition of the ionosphere has any effect. Like NEC, propagation software has considerable support, and the monthly “propagation” column in antenneX is only one example. Like the other programs that we have noted, propagation programs are limited by the adequacy of the input data and the algorithms by which they make their calculations.

In addition to these relatively large and cohesive programs, we find a vast collection of smaller utility and auxiliary programs, each covering a small area of concern. So great are the numbers and types of programs that a catalog is impossible. We can only indicate some categories and formats. For example, we can divide the programs into differences in their programming format. The largest collection of utility programs still comes in a GW-Basic form, namely, Hamcalc, by VE3ERP. You can obtain the latest version—which is set-up for installation on Windows XP—from www.cq-amateur-radio.com . The collection of individual utility programs is so large that a description is not possible. It includes very basic calculations, such as determining the resonant frequency of an inductance-capacitance combination, and relatively advanced and somewhat esoteric calculations, such as the Q of solenoid inductors and the impedance and gap required for flat-faced parallel transmission lines. In addition, although the program compiler has used accepted sources for his algorithms, the programs may be variable in the adequacy of the output for specific applications.

BEYOND THE BASIC
Basic-language programs have largely given way to spreadsheets as the specific form for handling many utility calculations. Microsoft’s Excel is almost universal, although Quattro Pro has a number of dedicated users. Most of the spreadsheets are free and available from numerous web sites. However, you will find a number of commercial applications. For example, AC6LA’s Multi-NEC Excel spreadsheet is widely used as a shell within which to use the NEC and MININEC core. The shell provides many useful functions not included in dedicated implementations of the modeling software. Multi-NEC and other AC6LA Excel programs are available via www.qsl.net/ac6la/index.html.

The spreadsheet user has a special responsibility in connection with free downloads. He must evaluate the spreadsheet to see if it is useful and adequate. Since numerous computer users are engaged in perfecting their spreadsheet programming skills more than in developing aids to precise antenna work, we often find that the equations placed into such utility sheets are rather gross simplifications of cutting and other formulas drawn from unknown sources and never subjected to proper scrutiny. On the other hand, some spreadsheets encapsulate very accurate equations and yield very precise results. The user must be knowledgeable enough to know the difference. The downloads that are available from antenneX come without certification and require that the user carefully evaluate their content.

An alternative to the spreadsheet is direct programming in a Windows-compatible format. For example, the Grayline CD-ROM by ON5AU (available from antenneX) contains a number of very helpful stand-alone utility programs to use in conjunction with propagation and communications work. As well, scripts are available for including a utility at a web site. You will find some algorithms available in a variety of formats. For example, W4RNL’s equations for calculating the dimensions of Moxon rectangles with uniform-diameter elements are available in Basic, spreadsheets, on-line script, and a stand-alone program from AC6LA.

MORE TO COME
We have only scratched the surface of the sorts of utility and auxiliary software available to ease the task of the antenna system and user designer, analyst, and user. For example, space does not allow us to list the numerous utilities appended to various implementations of NEC and MININEC, including antenna-optimizing routines. However, the same basic rules apply to every such software element. Select the format that you find easiest to use in your circumstances. Do not simply use the software, but learn as much as you can about its formulation so that you can understand both its capabilities and its limitations. Evaluate the software to determine its overall adequacy and accuracy. Finally, use the software not only to do specific calculations, but also to expand your understanding and appreciation of the phenomena that it calculates. Now, for an important announcement:

ACE-HF AND ANTENNEX
I am pleased to announce that antenneX has become an authorized distributor of ACE-HF's System Simulation & Visualization Software. Some refer to this as the "Cadillac" of HF Propagation Programs. The company's latest version v2.05 is now available in the software section of the Shopping Shack. Along with the launch of the Grayzone (utilities) CD-ROM last month, this product nicely expands the fine propagation tools we can now offer to the worldwide market.

ACE stands for "Animated Communications Effectiveness", a coverage display technique originally developed for U.S. Navy submarine communications. The ACE method shows a sequential series of coverage maps. When the maps are animated, a movie is shown. ACE-HF's advantage is that the effects of the day's passage may be easily understood and it shows when the HF bands will be open in different world areas.

WHY USE ACE-HF?
With ACE-HF, you can truly try-before-buy! Are you dissatisfied with your ham contacts and wonder how much better a new Yagi might work than your old Vertical? ACE-HF can tell you. Do you have a QSO schedule with a buddy on 40 meters and wonder how well your dipole antenna will support the circuit on 80 meters? ACE-HF can quickly model that antenna and show the effects on connectivity. And what about ham contests? Do your present antennas cover that missing country, or would it be worth the investment to put up a Yagi stack? Again, ACE-HF can compare the effectiveness of different antennas and automatically find the best band for each at every time-of-day. And, ACE-HF can do this for current conditions or for any month in the future! Talk about try-before-buy planning!

ACE-HF is much more than a propagation model, although it uses the worldwide gold standard VOACAP model as its computational engine. The key design focus is on system simulation—not merely signal propagation. With ACE-HF, signal-to-noise (SNR) calculations are always emphasized (although signal predictions may also be shown).

CONTESTING AIDS
With ACE-HF, you can now make simultaneous predictions for up to 18 separate circuits, and the results are displayed on a table. One can specify different antennas for each end of each circuit, and can even specify different antenna models for every contest band. The table shows color-coded SNR values for each frequency and can be animated through every time-of-day. You can easily see when different bands are “in the green,” and the best frequency is colored blue. The table appears for the current time and then advances automatically every hour. It’s a great tool for contesting as you can see at a glance the bands that are open, or can advance the time for planning your next contacts. In contests, it allows one to plan the "on" and "off" periods and operating bands in advance.

One can keep ACE-HF running in the background during the actual contest to compare the predictions against actual conditions to make the necessary mental adjustments and strategy changes as propagation dictates. Of course you can also "roll it forward" to show what conditions are likely to be like later in the day. Or to check when 10m will be open to Europe, to get some new multipliers on that band. There's also a nice beacon chart showing which beacons are active, and whether they should be audible.

ANTENNA COMPARISONS
Circuit group predictions may also be used to compare antenna effectiveness. ACE-HF permits the antenna experimenter to isolate propagation effects when comparing antennas. Both gain and pattern must be considered when comparing antennas, and ACE-HF also shows antenna pattern displays.

Many will be interested in the new ACE-HF capabilities for enhanced antenna analysis. In addition to the built-in HFANT program, with which the user can show antenna patterns for the many supplied antenna models or for models that he or she has created, there is a new animated chart for comparing antenna patterns with predicted elevation angles.

One of the most difficult problems in choosing antennas for your station is knowing the best vertical radiation pattern for a given circuit. This problem is particularly troublesome when short circuits that rely on NVIS (Near Vertical Incidence Skywave) propagation must be accommodated. For NVIS, a simple vertical monopole simply won’t do.

The new ACE-HF Selected Antenna Analysis Chart automatically graphs the antenna’s vertical acceptance (take-off) pattern along with elevation angles of the arriving propagation modes. The chart may be animated through the user’s assigned frequencies and directivity gain is given for each.

NEC Antenna Analysis with ACE-HF
Experimenters who have acquired the NEC-Win Plus+ or NEC-Win PRO antenna modeling software, available from antenneX, can save their antenna models in a VOACAP gain-table format called .ANT. Such files can then be used directly within ACE-HF to display antenna patterns or for use directly in circuit analyses or area coverage displays. (Such files use the standard VOACAP .13 extension when used within ACE-HF.) Or, customers who have acquired the L. B. Cebik antenna model CD from antenneX can use the NEC programs to save each model in the VOACAP format for use with ACE-HF.

AREA COVERAGE
One of the most powerful tools in ACE-HF is the animated area coverage display. When one creates files for all 24-hours, the display first appears for the current hour and advances every hour automatically. One can gain amazing insight when the area coverage displays are animated through 24 hours! Coverage comes and goes, quickly explaining why certain frequencies are preferred in contest situations. (One can also animate the displays as a function of frequency at any time-of-day.) What a great teaching tool for new Ham operators!

A fun experiment is to create sequential area coverage displays at a fixed time-of-day, varying the antenna’s azimuth setting in the ACE-HF model. If you create 36 displays, say at 10° intervals, ACE-HF will spin the antenna and show the resulting coverage changes as a movie!

If you've only used "point to point" or circuit based propagation software, then ACE-HF will be a very pleasant surprise!

Using ACE-HF, one can readily see why a circuit might be weak if it is found to be at one of the nulls in a multi-lobed radiation pattern.

To aid antenna pattern visualization, ACE-HF can also display the total pattern in a 3D chart, such as seen here on the right. This chart may also be animated through the frequency range and adjusted for viewing angle.

ACE-HF Accuracy
Radio experimenters sometimes ask which propagation program is the most accurate? Some years ago, the U.S. Navy funded the authors of ACE-HF to determine which HF propagation program was the most suitable for their HF networks. The resulting study selected VOACAP as the most highly validated model and it was then included in the ACE-HF software. VOACAP—widely regarded as the world’s gold standard—is based on the IONCAP operations research model, and was then improved by a rigorous development program funded by the Voice of America. During that development, every potential improvement was subjected to more than 500,000 circuit path-frequency hours comparisons with field data for paths at all latitudes and ranges.

There is so much more about this powerful tool to talk about, but only limited space available in this column. The reader is encouraged to read the details well organized and described at the product page in the Shopping Shack. There you will find a multitude of screenshots, some of which are animated examples.

And, as a final comment, folks find that the ACE-HF product support is first class! I've worked with one of the principals, Richard P. Buckner, P.E. for the past month or so and know about his penchant for quality and attention to details. These are good folks and we are pleased to represent their products. Take a look at this product—you'll be glad you did!

THE PURPOSE OF THIS JOURNAL
In my column for September 2006, “The antenneX Mission,” I wrote about a subject close to my heart — the purpose of this journal. It had been quite some time since I had reminded our readers of our original purpose when we set out some 20 years ago.

More than anything else, this journal has always been a “labor of love” for me. It is the reason I founded the antenneX magazine almost 20 years ago, knowing that running a magazine is a tough business and especially so since I planned to do it without the traditional revenue support from advertisers or outside investors. I wanted this magazine to always be able to write about any issue without concerns of losing the support from any of those type revenues. I am pleased to say, we have never steered from that course one iota. And, as a consequence, we have covered some very controversial developments throughout the past two decades. In the process, we have provided valuable factual information to more than 200 countries, even to the most remote regions of the globe. Hence, our readers are much more informed about the truth about all of the “new” devices as their stories unfolded in the antenna and antenna-related field. For more details, you are encouraged to read my column from September 2006.

Additionally, we were pleased to receive and publish in the October 2006 issue, a very special editorial reaction to my column written by one of our long-term readers and contributors, Dr. Jef Verborgt. Those two articles are located by the following links below:

VISIT THE GUEST ROOMS
The relentless attacks on our web site by pirates and the like has made it necessary to add more security to protect our material against such piracy. It's only fair that we know who enters the House of antenneX, so our guests will need to provide some minimal information in the process of obtaining a login. This includes using your real active email address without which a login cannot be received. Do not confuse this login with a paid subscription login. They are not the same and your subscriber login will NOT work in the Guest Room areas. Of course, you may choose to create your own login to the Guest Rooms using the same login as your subscription, if the system will accept it.

Along with the continuing fight against spam/virii junk, protecting our material and valuable bandwidth against piracy takes up a great amount of our time—time we can't really spare. The Internet is simply not the friendly neighborhood it used to be in the "old days" and more and more security must be installed to counteract these intruders. Thus, we have made the access to the Guest Rooms as automatic as possible for you to manage your own login.

In view of the above, we have overhauled the numerous free and open-access sections that have always been wide open to all of our friends throughout the many years antenneX has been online. But, we must change with the times as the need dictates. I don't think the Internet will become more friendly in the near future and protected sites with logins are fast becoming the rule rather than the exception. To repeat, most would like to know who they invite into their house. The same applies at the House of antenneX. It's really worth the effort!

We have activated a new login system for access to the above guest rooms — and, the login can be totally managed by our guests. Above is a graphic of what you see as a login page to the new consolidated area, "antenneX Guest Rooms." This new page for logins is at this location now and available for your use:

As a result of this new programming, you will be able to obtain your own login, change it to update your info, change your password and delete membership if & when you desire without our help. Of course, the bottom link on the new page provides help if you still need it.

AN INVITATION TO CONTRIBUTORS
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antenneX thrives on the contributions of antenna experimenters, ranging from the informal home shop construction project to the theoretical investigation of basic antenna, feedline, and propagation phenomena. Over the years, we have published articles on the use of new or newly adapted materials, known antennas adapted to new circumstances, modifications of antenna structures, basic explorations of both common and unusual antennas, antenna modeling exercises, design improvements, antenna matching techniques from both a physical and mathematical perspective, evaluations of mini-antennas and their underlying theory of operation, new and patentable designs, propagation tutorials, and.... The list goes on, since no antenna-related topic is irrelevant to the readers of antenneX.

At the same time, antenneX has experienced continuous growth in its readership—for which we are appreciative. However, all readers can help us do even better. How? By submitting an article every now and then based on your current antenna work that may be useful at any level to other readers.

Among the engineering and researching readers, there are undoubtedly a number of unclassified and non-proprietary findings that antenneX readers would like to know. Among the practical antenna designers, there are ideas, tests, and numerous other practical findings to benefit our readers. Antenna builders very likely have some techniques to share with other readers. Besides the regular articles, we always have the home work shop column for shorter practical ideas and we always have the invited news and editorial column for information about new technologies, future advances, lost old but good ideas, and personal views on the good to bad things that are happening in the world of antennas and propagation.

If you are uncertain about whether your ideas merit an article, please feel free to send an outline to the general editor/publishers at manuscripts at antennex.com . Do not feel that you must be ready to be a regular submitter to write for antenneX, because we welcome the individual contribution as much as monthly articles. As well, do not believe that the slots in each issue are already spoken for—we shall always make room for a worthy article.

Adjacent-Band Quad Behavior
By L.B. Cebik, W4RNL

In the study of quads that led up to some notes on dual-band antennas using a common feedpoint, I intentionally by-passed an important question. Dual-band quads required a frequency ratio of at least 1.3:1 for inclusion in the earlier notes. As a result, I omitted combinations such as 20 and 17 meters or 12 and 10 meters. That set of notes reached a number of conclusions about quad behavior based on consistent trends shown by the models that I did use. Foremost among the results was the observation that most of the major performance and dimension changes resulted from the simple proximity of the element loops, even when using separate feedpoints. The major dimensional change that occurs when using a common feedpoint instead of separate feedpoints is the lengthening of the inner or higher-frequency driver loop.

We are now positioned to fill in the gap in our exploration of dual-band quad behavior. The study can restrict itself to quads with separate feedpoints on each band, thus simplifying the required modeling.

Magnetic Field in a Time-Dependent Capacitor
By Kirk T. McDonald, PhD
Joseph Henry Laboratories, Princeton University

Here we, reconsider the classic example of the use of Maxwell's displacement current to calculate the magnetic field in the midplane of a capacitor with circular plates of radius R while the capacitor is being charged by a time-dependent current I(t). In particular, consider the displacement current density in MKSA units for vacuum between the plates, to consist of a collection of close-packed "wires" that extend from one plate of the capacitor to the other. Sum the magnetic field from this set of virtual wires to find the total field. Thus, the essence of this problem is to show that the magnetic field due to a circular bundle of n fine wires, each carrying current I/n, is the same as that of a single, fat wire that carries current I.

Baluns and Impedance Matching
By Fred M. Griffee, N4FG (EE Retired)

Here I would like to review a popular but not much used balanced impedance matching approach. After a short discussion about it, I discuss a similar balanced matching approach using an Amidon T-400-2A toroid powdered iron core. Then I discuss the use of baluns that allow unbalanced antenna tuners to be used that include consequent losses not experienced with balanced impedance matching networks and low loss balanced transmission lines.

In the process of analyzing and discussing these other impedance matching approaches, antenna current and power delivered to the antenna shall be addressed. Of course, the usual bottom line in all of these approaches is the overall antenna system efficiency. I address the choice by many to overcome power loss by using higher input power that actually experiences even more power loss although some additional power is radiated.

INTRODUCING ACE-HF PRO V2.05
By Richard P. Buckner, P.E.

The well-known ACE-HF System Simulation and Visualization software for Ham Operators and Short Wave Listeners is now available from the antenneX Shopping Shack. Long-term readers of the antenneX online magazine know that antenneX stands for antenna eXperimentation and experiments with radio antennas often can be aided by software simulation. Why build an antenna and measure its characteristics if we can first preview that antenna using software? ACE-HF software focuses on that need. For the first time, radio operators can simulate their entire HF system—including both transmit and receive terminal antennas, the propagation channel itself and the environment in which the system operates by using ACE-HF. ....and much more!

The Coaxial Folded Monopole:
A Modeling Adventure
By L. B. Cebik, W4RNL

The coaxial folded monopole lies at the base of the coaxial collinear array and a number of other antennas. The difficulty that designers and analysts have with the antenna lies partly in our inability to effectively model the relatively simple device. However, in principle, the antenna is as easy to understand as a simple folded monopole. This article outlines the basic considerations.

Coax Dipoles - An Overview
By Jan Gunmar, SM0AQW

Dipole antennas made partly from coaxial cables are surrounded by mystery. On the Internet there are statements like ”Coaxial dipoles – the best kept antenna design secret” and strong praise: “When I changed to a coaxial dipole my signal reports got 6 to 10 dB better from all continents”. No wonder that many are curious! This very comprehensive article on the subject helps sort out the mysteries and various configurations. Hats off to Jan who has produced a tremendous effort on this issue.

Well, there you have it, folks—thanks for listening and remember, the reading lamp is always on for you in the reading rooms. If I can be of further help, I'm just a Stone's Throw! away.-30-

Best reGARDS, Jack L. Stone, Publisher
jack@antennex.com
February 2007 antenneX Online Issue #118