If a man can only have one
kind of sense, let him have common sense.If he has that and uncommon sense, he is not far from genius.
— Henry Ward Beecher (1813-1887)
If a man can only have one
kind of sense, let him have common sense.
If he has that and uncommon sense, he is not far from genius.
— Henry Ward Beecher (1813-1887)
When You Compare Antennas
By Jack L. Stone, Publisher
INTRODUCTION
ntenna
comparisons appear in almost as many forms as we have types of antennas. They share
something in common: most of them are expressed as loosely and as vaguely as the
protestations of love by a young man not ready for a long-term commitment. (We used to
say, "not ready to settle down.") Yet, the process seems simple enough. We only
need to say how two (or more) antennas are alike and how they are different. Most of us
learned how to do that as far back as Sesame-Street days.
One factor that gets in the way of making precision comparisons is our acceptance of advertising hype in the field of antennas. Amateur antenna ads are full of intentional obscurities, but they are not alone. Commercial spec sheets also do their best to obscure what they do not want to show. Whatever the frequency range, function, or type, most spec sheets show the bare minimum of so-called representative radiation patterns. In the world of selling antennas, you can bet that "representative" really means "the very best that we could generate," whether the source is a model, a set of independent calculations, or a range test.
Similar considerations apply to gain specifications. Some makers use free-space gain expressed in dBi. Others use free-space gain expressed in dBd (always 2.15 dB lower than the same gain in dBi. Some use the gain at 1 wavelength above ground expressed either in dBi or in dBd. The dBd version rarely specifies that there was a standard dipole reference antenna at the same height, so the basis of the claim remains obscure. As well, consider a Yagi designed for several bands, such as the amateur 20-, 15-, and 10-meter bands. Claims taken at a 1-wavelength height represent different physical heights for each band. An actual installation is not likely to change height with each band change. However, whatever the height in feet or meters, the 10-meter active elements are twice as high as the 20-meter active elements when measured in terms of wavelengths. A few makers specify their antenna using a physical height, although they may use either dBi or dBd as the gain unit. If we place all the spec sheets on a table, one might make a content to see who can sort them all into the order of gain from highest to lowest in the shortest time. However, you must have great patience waiting for a winner to emerge.
Front-to-back performance is even more confused and confusing, since we lack basic standards. Few antenna manufacturers (amateur or commercial) closely specify which front-to-back measure they are using. Some use the 180-degree front-to-back ratio, although this measure often inflates the value if the rearward lobes show a deep null in the direction. Some use a worst-case front-to-back measure, which takes the highest gain in any rearward direction and compares it with the forward gain. To make matters worse, some specifiers call this the front-to-rear ratio. However, the front-to-rear ratio has another meaning: an averaged front-to-back ratio taken by sampling the rearward lobes at many points along the rearward semicircle. In fact, some antenna makers call this the average front-to-back ratio.
Most commercial and amateur antenna makers simply list gain and front-to-back ratios in terms of raw entries. Sometimes they call the entries "typical." What they do not show is how typical the antenna numbers are across any particular operating span. Rarely does the buyer see a graph of either gain or front-to-back ratio, so he or she cannot tell if the range of values is high or low or whether the values favor one or the other end of an operating passband. Usually, the only value graph shown is an SWR curve, and as often as not, it looks more contrived than measured or modeled.
When we reach the level of qualitative claims, the specification sheets become even vaguer. Terms like "high performance" and "superior performance" abound, but the sheets never say for what purpose the performance is high or over what the performance is superior. Gain is not everything. In fact, some receiving applications require low-gain, narrow-band, low-noise antennas, in contrast to broadcasting and amateur applications that seem to rest on applying more power and gain to overwhelm the target station or audience. One commercial maker actually specifies his end-terminated inverted-V offering as a "higher-gain" antenna for wide-band use.
The prevalence of such verbal antics presents the experimenter with a series of temptations that we should all avoid. One is the use of anecdotal customer-satisfaction quotations. The equivalent experimenter remark is success in making a few contacts with a new antenna design. Another temptation is the use of single-frequency performance specifications without reference to variations across an operating passband--unless the application for the antenna is its use on a single frequency. A third temptation is the use of received S-units as a precision measure--unless one is comparing two antennas using the same receiver. A fourth temptation is to show test results without any kind of description of the environment in which the tests occurred. To keep this list short, I* shall add only one final entry: the use of general evaluative terms without expressing them in terms of some set of broadcasting, receiving, or communications goals and parameters.
We do not all have access to well-designed test chambers or to ANSI-rated test ranges. Our measuring equipment may be rudimentary--and some of it made in our own shops. Nevertheless, when we make comparisons--or even just imply them silently--we should make every effort to be a clear and precise as possible. As well, we should set up a detailed context of evaluation so that any comparisons will be both relevant and self-limiting. Your antenna A may be better than some alternative B, but always for a purpose and within a well specified set of limits.
A DEDICATION
Now, for a somber moment. Please indulge me a moment to express my grief at the loss of my
beloved Mother, to whom I owe everything, for without her, I would not be—nor, would
this magazine be for that matter. This month's Issue is dedicated in her memory.
On the night of January 27, 2006, Mom's beautiful life force evolved to another heavenly form after a brief struggle with inoperable cancer. I have kept and cherished all of the pictures she sent me throughout my life. I located this picture collage I made for her some years ago. It was her favorite. It strikes all kinds of emotions for me, as it did for her, for at least we could be joined by the collage though separated by thousands of miles of geography much of the time as our separate lives winded their different ways dictated by fate.
~ In Memory of
Mother ~ — Mi
madre va con el dios |
The nostalgic and sentimental collage above contains two shots of each of us—Mom at 17 and 21 and myself at one month and later as an adult. Indeed, she married my Dad, William at the tender age of 16. Dad was 18 with good employment. It was not unusual for Texans in those early days to marry at such a tender young age. As her first born, the "Stork" delivered me almost a year later. Mom is survived by three sons, two sisters and a bunch of grandchildren.
She was a beautiful and loving Mother, possessing great strength, courage, and common sense—she was independent throughout her life of 85+ years until the end. I loved and admired her greatly and believe she was proud of her first-born son.
Mom's ancestors, the Lynches, arrived in Texas in the mid-1800s. The "Stone Clan" arrived in 1836 when Texas was still a Republic. Both were brave, pioneering families. Texas was not yet tamed and still a bit dangerous in those days with wars that raged on through the mid-1800s with the Native-American Indians and Mexico. It was not until 1845 that Texas became the 28th state of the United States. Texas was always in her heart, but her soul is in the loving family that carries her memory.
But O the heavy change, now thou art gone, and never must return! — John Milton (1608-1674)
Tune in for more news and
topics next month.
This month's Issue by our fine writers is introduced below.
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The new Antenna Discussion List is a infinite fountain of ideas making it a great "watering hole" for exchange of ideas, questions and answers on a wide range of antenna-related subjects. You will be in good company along with some of the brightest minds available. Were else would you have such free access to this level of expert advice? To participate or just read along on some very interesting subjects each month with 2000+ members from all around the globe, you are welcome to join us:
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AN INVITATION TO CONTRIBUTORS
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
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At the same time, antenneX has experienced continuous growth in its
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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
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old but good ideas, and personal views on the good to bad things that are happening in the
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If you are uncertain about whether your ideas merit an article, please feel free to send
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To see details of our writing guidelines, please look at: Writing for antenneX
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IN THIS ISSUE
This month is our 105th issue online! We again include many fine articles by our great writing team. Now, allow me to introduce this month's line-up of content:
OUR MONTHLY COLUMNS (plus this one you are reading by yours truly):
FEATURE ARTICLES IN THE LIBRARY:
Wide-Band
40-Meter Yagis |
| In Part 1 of our expanded notes on wide-band 40-meter Yagis, we looked at
some standard and non-standard Yagi design ideas. The 2- and 3-element Orr-derived Yagis
employed wide element spacing to accomplish 2 goals: to raise the general feedpoint
impedance to the 50-Ohm level and to increase the operating passband to cover all of 40
meters with under 2:1 SWR. However, only the relatively long-boom 4-element Yagi that used
a master-slaved dual driver system achieved the most desirable end of having well under
1.5:1 SWR across the band while raising the gain level to about 8 dBi in free space. We
also examined the recent N4HBX reflector-less design that employed a fed driver and
bracketing slaved drivers to obtain about 7 dBi gain with under 2:1 SWR across the band. As we closed Part 1, we noticed that we had not exhausted all of the design options that we might apply to Yagis in order to achieve full band coverage. In this Part 2 of the notes, we shall take up the design challenge in 2 directions. |
Using
“Cans” and Sleeves in Antenna Construction, Part 1 |
| The
idea of using sleeves in antenna structures is not new. In the book Antennas, Transmission
Lines and Waveguides from 1946 by R W P King et al, a number of interesting applications
of sleeves are described, for example devices to suppress unwanted feeder currents and as
phase shifters in collinear arrays. One of several applications shown in the book is the
following antenna:
|
An End Fed ZEP Antenna Analysis, Part I |
| Often, it is not convenient to install a simple dipole configuration. An antenna such as the end-fed-ZEP (EFZ) antenna using a single wire feed or else some sort of chosen transmission line may be more convenient. This month's exercise shall use 600-Ohm transmission line for an EFZ antenna feed line and in addition, the analysis shall include comparison between one using radial wires and one using none. |
A
10 to 40 Meter Screwdriver Antenna |
| In a
previous issue of antenneX (now in Archive No. 8) we showed how one can build a
“continuously variable coil”. We now will take it one step further and show you
how to build a variable 10 to 40 meter screw driver antenna. For a better understanding of
the project let’s first have a good look at this picture. For those interested in
screwdriver-type antennas, join us this month in this well-illustrated article about this
interesting project that serves with great results.
|
Experiments on Loops above Ground |
 antenneX readers, especially those who contribute to the antenna discussion forum, find the subject of loop antennas perennially interesting. Usually the loops under discussion are small magnetic loops, with circumference very much less than a wavelength. In this article, some experiments on the radiation resistance and resonant frequency of FULL WAVE loops are presented. |
THE
CONJUGATE MATCH |
 Amateur
Radio has always been a technically oriented hobby. Over the many decades of its
existence, the Amateur has made very significant contributions to this technically
oriented field of radio frequency (RF) communication. The advancement of the technology
has been remarkable causing it to be a significant challenge to learn. But an Amateur is
one who is interested in learning how something works as well as how to use it. Because of
the Amateur’s technical interests and skills plus, the myriad advancements made by
Amateurs have helped to further advance RF communication. Antennas, or better said, "antenna systems" are a popular topic. RF energy and RF circuits have perhaps had more than their share of myths, misunderstanding and plain bad information. This is probably occurring because, of all the forms of energy employed, RF energy is hard to see and measure and therefore the hardest to understand. Measuring or proving a concept is often complex due to the interactive nature of measuring RF. Much of what we learn has to be taken as truth from a source that we trust, simply because we don’t have the well-equipped lab to test and prove a concept. |
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 2006 antenneX Online Issue #106
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with questions or comments.
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Last modified:
December 31, 2010
This antenna has been re-invented many times since the middle of the fifties; there is
even one fairly recent variation, which is called a “Mystery Antenna” by its
originator! In this article, we have opened up this "mystery" a bit further.