Use and Abuse of Antenna Specs Revisited

Happy is he who gains wisdom from another's mishap.
—Publilius Syrus (1st C. B.C.)

INTRODUCTION

n a past Stone’s Throw, we looked at some of the difficulties that amateur radio operators have when trying to meaningfully compare specifications for antennas that seem to be similar—or at least comparable. We can summarize some of the problems succinctly.

1. Gain: Some makers use dBi, others use dBd. Some use figures for the antenna at a height; others use free space. Those who use the antenna at a height do not use the same height (one uses a set height in wavelengths, another use a height in feet. Some use a 2.15 dB adjustment between dBi and dBd; others report gain in terms of a dipole at the same height as the antenna for sale. Hardly anyone provides graphs across the operating band. Some report peak value, while others report average values.

2. Front-to-back ratio: Some use the 180° values; some use the worst-case value; and some use an averaged front-to-rear ratio. However, some call the worst-case version a front-to-rear ratio, while other call the average front-to-rear ratio an average front-to-back ratio. Again, graphs are very rare.

3. Impedance or SWR: Some report only the maximum value. Others report the best value. Some provide graphical curves, but others report an SWR passband limit.

4. At VHF, where long-boom Yagis, Quagis, and Quads are common, information on sidelobe strength is often vague, and details of sidelobe structure are almost non-existent.

5. Vertical arrays for amateur service show no consistency in the ground medium used as the basis of specifications, whether it is perfect or real, and if real, what the test ground quality was. As well, specifications for any required radial system are missing.

6. A few makers provide details on the system and conditions of measurement, but in most cases, details are rare.

YET MORE CONFUSION
These are not all of the problems that a consumer faces when contemplating the purchase of a commercially made antenna, but they are enough to indicate the size of the challenge of trying to spend hard-earned dollars to best effect. Although the amateur community has retreated wisely from some of the extravagant claims made in the 1970s and 1980s—or perhaps because of the retreat—confusion still reigns in the world of competing antennas.

Amateur radio is not the only service in which considerable money goes into commercially made antennas. Indeed, the amateur segment is only a small part of the antenna world. Here are a few other segments of interest.

1. Citizens Band: If amateur specifications must at least sound plausible compared to the many sources of information on antenna performance, CB antenna makers suffer no such restriction. 11-meter antennas have a history of outlandish claims for performance. Perhaps the classic claim was made decades ago by a seller of hollow-tube antennas, which claimed additional performance over similar appearing ones due to the alcohol that filled the cavity.

2. AM BC: For regulatory reasons, AM broadcast antennas use a special set of specifications. The specifications, however, as self-consistent within the industry and tend to focus on aspects of antenna performance that other segments of the world of antennas tend to ignore. Anyone who enters this realm from an engineering and licensing perspective may find difficulties communicating clearly with someone whose interest in antennas is more general, or theoretical. Since each installation usually represents a singular engineering project, comparative difficulties rarely arise.

3. Television: Cable almost did in the TV antenna industry, but the advent of satellite services has re-awakened it, since dish-type service requires local reception by antenna unless one meets certain excepting conditions. TV antennas have always been somewhat like CB antennas, where marketing claims outweighed straight technical information. However, in many cases, antennas suited to simple analog TV are proving inept when it comes to dual-channel high definition TV.

4. WIFI and relatives: Current “high frequency” (meaning high UHF and upward) antenna sales come in two major sorts. One set is subject to engineering rules where a complex installation must either perform or not be accepted by the customer. However, there is also a consumer market for antennas to extend computer wireless, cell phone, and other services beyond the normal limits of local coverage. Little antennas—in principle not much different from those magic TV-set-top devices of olden days—are now sprouting at every retail store. They have no real specifications in most cases, but are merely guaranteed to work—until you request a refund because they do not work.

5. Government and military installations: The purchasing system by U.S. government and military installations has made mincemeat of antenna specifications. The problem lies less in the specifications, and more in two other aspects of the acquisition system. One facet involves the relative ignorance of those who review submissions. The agents tend to know more about the paperwork and boilerplate than they do about the reasonableness of the claims made on the submission. The second facet is the well-documented insider relationships that tend to rule the decisions regarding antenna purchases and contracts. Every major commercial maker will have an on-site representative at major installations. The individual’s job is multi-faceted. He befriends the site powers. He obtains inside information on competing submissions. He then has his company create “new” systems with higher performance specifications than the competition. The makers use every technique available to inflate the performance potential of their offering within the limits of what can be justified by pouring a pile of words and equations into a document. Sometimes the claims are technically sound; sometimes they are not. But the on-site representative does not worry for two reasons. First, he knows the contract is his if only his paperwork looks right. Second, these are only tax dollars.

STAY INFORMED IS BEST ADVICE
The list might go on, but we have shown enough diversity to display the challenge facing strict conservative antenna specification readers. If only the government had a system of rigorous technical review. If only consumers were more knowledgeable. If only manufacturers let engineers write specifications rather than turn them over to the creative writing talents of marketing departments. It is unlikely that we shall ever see a structural change to allow engineering honesty into the many social domains involved with antenna. Perhaps the best that we can hope for is occasionally alert and informed individuals. Hence: Happy is he who gains wisdom from another's mishap. —Publilius Syrus (....or careful research from the experience of others —2007 AD)

NEW CONTRIBUTORS THIS MONTH
Our readers will note we have several interesting feature articles this month by some new contributors. Although the articles are introduced as usual in my lineup toward the bottom of my monthly columns, I bring your attention to these authors:

Why an Antenna Radiates by Ken Macleish, W7TX — A rather controversial topic as are the theories that surround it. This article, no less controversial, was among some very spirited discussions on the antenneX antenna-discussion forum.

Ken Macleish received his first Amateur Radio license 60 years ago at age 12. He now has an Extra Class ticket and still enjoys ham radio, especially CW ragchewing.

He holds a BS in physics (1939) from Caltech and a PhD in physics (1943) from the University of California at Berkeley. He was with Tennessee Eastman Company at Oak Ridge, Tennessee, during World War II, then transferred to Eastman Kodak in Rochester, New York, where his most recent position was assistant director of research and engineering in the Kodak Apparatus Division. In 1962 he joined the Perkin-Elmer Corporation in Norwalk, Connecticut, as a vice president of engineering. He retired in 1970 to enjoy the climate and scenery of Arizona.

Ken has authored QST articles on frequency counters and frequency measurement. Also, over the years, he's had a nagging desire to understand why a radio antenna works. Combining this desire with a background in physics, a hobby of ham radio and an interest in computers, Ken has been working off and on for some time to help dispel some of the mystery surrounding this subject.

Putting a Balun and a Tuner Together by Kevin Schmidt, W9CF — Baluns are a world unto themselves even though many articles have been written. Kevin provides his own unique twist on this esoteric subject material.

Kevin Schmidt is a physics professor at Arizona State University in Tempe and a fellow of the American Physical Society. He primarily does research on quantum many-particle simulations using and developing Monte Carlo techniques.

Kevin spends part of most summers at the Scuola Internazionale Superiore di Studi Avanzati (SISSA) in Trieste.

First licensed as WA9THN in 1966 changing to W9CF in 1977, Kevin enjoys casual contesting, occasional ragchews, and working on boat anchor equipment.

A Phased Field Antenna by Bill Graham, VE3ETK — Here's another antenna design concept that is bound to generate some more spirited debates on our antenna-discussion list this following month. In this article, Bill introduces his PF4-20 he describes as a real winner.

Bill Graham worked at CFPL-TV as a Production Technician in the 1950's. He moved to CFTO-TV as an Audio Engineer, then to CHYM-AM/FM in the mid 1960's to serve as Chief Engineer.

His first radio license was issued in 1964. The years that followed were busy with consulting work and designing radio and television studios, culminating with a six-week stint in Singapore.

Now retired, he enjoys all aspects of Amateur Radio.

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.

Notes on Wide-Band Multi-Wire "Folded Dipoles"
Part 1: Some Idealized Illusions
By L. B. Cebik, W4RNL

In an earlier article, I briefly touched on the 3-wire version of the antenna. In this note, I want to expand a bit on that antenna as part of a larger look at multi-wire "folded dipole" antennas using a terminating resistor to extend the SWR bandwidth. In fact, we shall review and expand coverage of 4 antennas: the standard single-wire doublet, the most familiar 2-wire terminated version, the sometimes mis-drawn 3-wire version, and a 5-wire version of the antenna. The goal is to enlarge our understanding of how these antennas work and what features count as advantages and disadvantages of them.

In the process, we shall examine some interesting properties of models of wide-band multi-wire terminated antennas based on idealized models. There are some techniques of model formation that are very useful under certain circumstances. However, if inappropriately relied upon, they can mislead us. As well, we may sometimes collect only partial data from an antenna model and be equally led astray. In this first part of the exercise, let's allow ourselves to be led and see where the path may wind.

The Fields of a Pulsed, Small Dipole Antenna
By Kirk T. McDonald, PhD
Joseph Henry Laboratories, Princeton University

We have another interesting contribution from Kirk this month on a topic spawned by our antenna-discussion forum:

The Problem:
Deduce the electromagnetic fields of a small dipole antenna whose time-dependent electricdipole moment p(t) is given.

A Solution:
Analytic descriptions of the fields of pulsed, finite-sized antennas are only approximate. In general, numerical simulations are required for detailed characterization of the fields of pulsed antennas. For example, we note that an “exact” form can be given for the fields in both the near and far zones of a pulsed dipole antenna in the limit that the size of the antenna is vanishingly small. One approach to a solution is based on the well-known electromagnetic fields of an oscillating “point” electric dipole located at the origin, whose dipole moment is expressed in equation #1 of this article.

Baluns and Antenna System
Network Impedance Matching, Part II
By Fred M. Griffee, N4FG (EE Retired)

In this episode, the results of attempting to design a balun approach that finds an acceptable efficiency for all bands (equal to or greater than 90 percent) and balanced currents with my present antenna and transmission line is discussed.

Consideration will be directed towards using an unbalanced L matching network with a coaxial bead choke balun at the input that experiences sufficient common mode isolation. Quite clearly, if the network can be isolated from ground, then balanced currents and very good efficiency should be experienced and be absent from unwanted common mode effects with continued attention given to efficiency, power delivered to the antenna, and balun (transmission line transformer) winding characteristics.

Various balun ratios and complex impedance terminations are compared and for all the data collection exercises, the MFJ 835 balanced RF ammeter is used. Again, in all of my previous articles and discussion in these areas, only the HF spectrum of frequencies (1 to 30 MHz) is addressed.

Putting a Balun and a Tuner Together
Kevin Schmidt, W9CF

Commercial antenna tuners use unbalanced circuits such a Pi-, T-, or L-network to match unbalanced loads to 50 ohms for our transmitters. A simple way to include the capability to handle balanced loads is to include a balun somewhere in the circuit. Johnson Matchbox tuners, which are no longer produced, but can sometimes be found at Hamfests, have a balanced output circuit and a link coupled input to make the transformation from the unbalanced input to a balanced output. Some hams still build tuners this way too.

Since a simple multi-band antenna is a center fed wire fed with twinlead or window-line to an antenna tuner, a beginning ham (and even some old timers) can wonder what is the best or at least a good way of handling the two jobs of impedance matching and changing from twinlead or window-line from the antenna to coax at the transmitter. Some typical solutions are summarized as well as exploring other methods.

Why an Antenna Radiates
By Kenneth Macleish, W7TX

You don't have to know how an antenna works to use one, but getting a handle on this subject can deepen your understanding of radio. Here's a searching look at the mysterious process by which our antennas hurl energy from Here to There.

If antennas didn't radiate, we might be well advised to dispose of our ham gear and take up another hobby. Fortunately, they do radiate. Our purpose here is to explore the basic principles underlying this wonderful and little-understood phenomenon. -- At least this author's view for your consideration.

A PHASED FIELD ANTENNA
By Bill Graham, VE3ETK

In early 2004 I got excited about the developments in antennae – that is an antenna where the E (electric) and H (magnetic) fields were brought into phase to produce improved reception and transmission. The difficulty with published information was that the designs were primarily created for the broadcast industry, or used broadcast concepts that didn’t take into account the needs of the radio amateur. It became clear that a new approach was required that would meet the needs of the amateur, and yet incorporate the principles of Poynting’s work with phasing.

Antennas that are designed to phase both the E and H fields require one to give up a lot of the traditional thinking one may have stored up in the mind based on conventional dipoles, etc. You must open your mind to new thinking – remember, it is the final result that really matters. Often when one thinks of phasing the thought is only about electrical phase. There is also physical phase, where two (or more) items are moved in relation to each other. If these items carry electromagnetic fields, then those fields are also moved.

And now I respectfully introduce, the VE3ETK PF4-20 Antenna - A REAL WINNER!.

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
April 2007 antenneX Online Issue #120