An idea, unless acted upon,
is not really an idea. - Jack L. Stone (I think)An idea, unless acted upon,
is not really an idea. - Jack L. Stone (I think)
About Those Test Results
By Jack L. Stone, Publisher
INTRODUCTION
ore than two years ago in my column entitled "Checking Those Claims"
for the April 2003 issue of antenneX, I briefly discussed the fact that it's
quite amazing how long claims about performance are allowed to perpetuate in the field of
antennas—not just compacts, but many conventional antennas as well. This is really a
caveat emptor business. It doesn't need to be so because it's not all that hard or
expensive to do sufficient measurements to check those claims. But, the next question is
how best to test—besides waiting for the test of time?
One of the significant questions that appears on the antenna-discussion lists from time to time involves the testing of new antenna ideas and products. In broadest terms that question is simple: what counts as a fair test? However, as many discussants have shown-both directly and indirectly-the question is not as simple as it appears.
So far, I have gleaned a few criteria for fair tests. My statements are expressed in very broad terms—just not quite so broad as the central question.
1. The test must be relevant to the type of antenna being tested. Different antenna types may require quite different testing procedures, even if all of them use similar measures, such as field strength. A commercial product like the Isotron might require quite different test set-ups than a new mobile antenna. Of course, testing an antenna for the lower HF range will present different testing challenges than an antenna for VHF or UHF use.
2. Most tests seem to involve a standard antenna against which to measure the new antenna. As some recent discussion has uncovered, coming up with standard antennas for comparative measurements is not as easy as it may seem. In general, we seem to know that we should compare horizontal antennas with other horizontal standard antennas and vertical antennas with other vertical standard antennas. But "standard" standards seem to be more elusive.
2a. One way around this quandary is to test a collection of antennas, all of which are intended for generally the same type of service. This procedure appears in the 2 Sliver-Morris volumes on HF beams and HF verticals. They used the same test situation (including a single tower for the HF beams, tested one at a time), along with instruments calibrated as carefully as possible. Their procedures allowed them to say that antenna A was better than B is some specific ways, and B was better than A in others. In the end, their conclusions about performance established a purely relative scale of performance.
2b. The alternative to the Silver-Morris methods appears to be the establishment of some standard antennas, such as vertical monopoles, dipoles, etc. With the wide geographic separation of folks who might perform such tests, it would be useful to have some detailed descriptions and follow-up discussion of antennas that may serve as standards. They should be antennas that most potential testers could replicate accurately in home shops. They should not require esoteric materials or construction techniques, although it is inevitable that some readers with great machine shop skills may produce highly refined versions of standard antennas. Simple antennas may be easiest to standardize. However, a baseline antenna for mobile service or a baseline antenna for comparison with antennas that rely on feedline radiation may be more difficult to formulate.
3. Antenna testing, using whatever standard may be appropriate, requires some instrumentation. What are the best instruments for the task of comparing antennas? What are the minimum instrument requirements for reliable testing? How can potential testers obtain (beg, borrow, buy?) at least the minimum adequate instrumentation for reliable testing? Can the circuit-builder produce adequate instruments at his or her own bench?
4. Good antenna testing requires a range. At upper VHF and UHF, special chambers come into play. Can one design and build from home-center materials an adequate chamber? For lower frequencies, fields, masts, and similar paraphernalia come into play. What are the ideal standards for a test range? What are the minimum requirements for a range from which we can draw reliable conclusions? What are the best methods for preventing a test antenna and a standard from interacting in ways that mess up the results. In other words, what are the operational as well as the physical requirements of a good test range?
I have probably missed some important aspects of antenna testing. Some of the ideas and questions come from the antenneX archives, where there are many instances of antenna testing. Some of the testing situations have had laboratory precision, while others used simply the best situation that one might set up in a back yard. Some of the ideas might be very serviceable; others might be ones to avoid in the future. Still others might require refinement before they achieved reliable results.
We all know that a few on-the-air contacts neither prove nor disprove claims made about an antenna idea or product. Some of the easy contacts made during the sunspot peak might not be so easy these days if we are testing HF antennas. At the other extreme are rated ranges and well-equipped laboratories funded by government or commercial monies. The tests performed by contributors to antenneX fall somewhere between these distant points.
Not all testing has to reach the same level to be useful. Some precision testing under fully controllable circumstances may be decisive and definitive. At a lesser but still refined level, we may have testing that uses comparisons to reveal strengths and weaknesses of the antenna under test. Still other testing may only shows a few trends or otherwise be suggestive. Whatever the level of testing, we do need some practical guidelines and guidance, along with practical information of the how-to nature.
If you think that these notes are one way to encourage future
contributions to antenneX, you would not be wrong. However, there is more to
these notes than just future articles. antenneX publishes tests of antenna ideas
and products, and we wish these items to be of the highest quality and reliability that we
can obtain. It is a matter of keeping trust with our readers. We do this when we apply to
any test the highest testing standards 
that
we can reach-and when we explain fully what our testing methods, procedures, and
instruments are. If we can help others improve in any testing department, we help all of
us with interests in antennas.
NEW BOOK RELEASE
During August 2005, antenneX announced the release a new and special
470-page book.
SMALL & EXOTIC ANTENNAS
A Compendium of Evaluations
Learn the Real Performance from the Experts!
ELIMINATING RUMORS & CONFUSION
This book has been needed for a long time and is especially aimed at reducing the
confusion about the most talked-about compact antennas. It contains 50 chapters of the
theory, construction, use and test performance of some of the most popular compacts. The
Isotron is only one of 12 different groups of "compacts" that have emerged
within the past 20 years analyzed in this one of a kind book.
For more details, please click on the URL below:
http://www.antennex.com/Sshack/eval/eval.htm
TOM'S TOWER OF TROUBLE
Speaking of antennas and the test of time, take a look at Tom's (Tom Cox, KT9OM)
continuing saga this month about his brand-new 120-foot tower versus the test of the ice
storm. Part 1 about his use of the "wrong stuff" appeared in last month's issue
as Tom learned his expensive lesson about researching the proper materials to use and
withstanding the extra weight of thick ice, plus the wind factor.
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Also, Tom sent in a short movie clip from atop the damaged mast
that can be seen here:
http://download.antennex.com/listarch/media/tomtower.htm
As a sidebar, Tom further contributed an editorial this month with the subject being about his particular writing style versus the "heavy hitters" as he calls them. Those who might be holding back on submitting an article for fear of doing the submission will find this interesting. I liked it because it was so spontaneous and perfect for the "soapbox" platform provided by the column, From the Shack. Tom's article can be seen HERE.
To see more specific details of our writing guidelines, please look at: Writing for antenneX
MORE COUNTRIES JOINED LAST MONTH!
Countries number 201 & 202 just joined the listing of
"Where in the World is antenneX?" As is our custom, we welcome the
latest newcomers and try to tell a little about the countries, some of the history and any
other things our research discovers that might be of interest. The US CIA's World Factbook
is most helpful in this research. A warm welcome to our latest newcomers!
WELCOME TO THE DJIBOUTI, COUNTRY #201
Background:
The French Territory of the Afars and the Issas became Djibouti in 1977. Hassan Gouled
APTIDON installed an authoritarian one-party state and proceeded to serve as president
until 1999. Unrest among the Afars minority during the 1990s led to a civil war that ended
in 2001 following the conclusion of a peace accord between Afar rebels and the
Issa-dominated government. Djibouti's first multi-party presidential elections in 1999
resulted in the election of Ismail Omar GUELLEH. Djibouti occupies a very strategic
geographic location at the mouth of the Red Sea and serves as an important transshipment
location for goods entering and leaving the east African highlands. The present leadership
favors close ties to France, which maintains a significant military presence in the
country, but has also developed increasingly stronger ties with the United States in
recent years. Djibouti currently hosts the only United States military base in sub-Saharan
Africa and is a front-line state in the global war on terrorism.
Location:
Population:
477,000 (July 2005 est.)
Life expectancy at birth: (2005
est.)
Total population: 43 years
male: 42 years
female: 44 years
Economy - overview:
The economy is based on service activities connected with the country's strategic
location and status as a free trade zone in northeast Africa. Two-thirds of the
inhabitants live in the capital city, the remainder are mostly nomadic herders. Scanty
rainfall limits crop production to fruits and vegetables, and most food must be imported.
Djibouti provides services as both a transit port for the region and an international
transshipment and refueling center. Djibouti has few natural resources and little
industry. The nation is, therefore, heavily dependent on foreign assistance to help
support its balance of payments and to finance development projects. An unemployment rate
of at least 50% continues to be a major problem. While inflation is not a concern, due to
the fixed tie of the Djiboutian franc to the US dollar, the artificially high value of the
Djiboutian franc adversely affects Djibouti's balance of payments. Per capita consumption
dropped an estimated 35% over the last seven years because of recession, civil war, and a
high population growth rate (including immigrants and refugees). Faced with a multitude of
economic difficulties, the government has fallen in arrears on long-term external debt and
has been struggling to meet the stipulations of foreign aid donors.
Communications:
Telephones - main lines in use: 9,500 (2003)
Telephones - mobile cellular: 23,000 (2003)
Telephone system:
general assessment: telephone facilities in the city of Djibouti are adequate as are the
microwave radio relay connections to outlying areas of the country
domestic: microwave radio relay network
international: country code - 253; submarine cable to Jiddah, Suez, Sicily, Marseilles,
Colombo, and Singapore; satellite earth stations - 1 Intelsat (Indian Ocean) and 1
Arabsat; Medarabtel regional microwave radio relay telephone network
Radio broadcast stations: AM 1, FM 2, short-wave 0 (2001)
Television broadcast stations: 1 (2002)
Internet country code: .dj
Internet hosts: 702 (2004)
Internet users: 6,500 (2003)
WELCOME TO THE VANUATU, COUNTRY #202
Background:
The British and French, who settled the New Hebrides in the 19th century, agreed in 1906
to an Anglo-French Condominium, which administered the islands until independence in 1980.
Location:
Population:
206,000 (July 2005 est.)
Life expectancy at birth: (2005
est.)
Total population: 63 years
male: 61 years
female: 64 years
Economy - overview:
This South Pacific island economy is based primarily on small-scale agriculture,
which provides a living for 65% of the population. Fishing, offshore financial services,
and tourism, with about 50,000 visitors in 2004, are other mainstays of the economy.
Mineral deposits are negligible; the country has no known petroleum deposits. A small
light industry sector caters to the local market. Tax revenues come mainly from import
duties. Economic development is hindered by dependence on relatively few commodity
exports, vulnerability to natural disasters, and long distances from main markets and
between constituent islands. GDP growth rose less than 3% on average in the 1990s. In
response to foreign concerns, the government has promised to tighten regulation of its
offshore financial center. In mid-2002 the government stepped up efforts to boost tourism.
Agriculture, especially livestock farming, is a second target for growth. Australia and
New Zealand are the main suppliers of tourists and foreign aid.
Communications:
Telephones - main lines in use: 6,500 (2003)
Telephones - mobile cellular: 7,800 (2003)
Telephone system:
general assessment: NA
domestic: NA
international: country code - 678; satellite earth station - 1 Intelsat (Pacific Ocean)
Radio broadcast stations: AM 2, FM 4, short-wave 1 (2004)
Television broadcast stations: 1 (2004)
Internet country code: .vu
Internet hosts: 512 (2003)
Internet users: 7,500 (2003)
VISIT THE NEW 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 nine 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 logins are 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!
This list pertains to those sections with free access now in our new Guest Rooms we have built and fully operating:
• Antenna Science
• Preview Articles
• Software Download
• Antenna Modeling
• From the Shack
• Propagation
• Ham WorkShop
• Stone's Throw!
• Discussion Forums
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:
Get you login all setup now at this URL:
http://www.antennex.com/guests.html
We've really tried to make it easy while still fending off the bad guys, i.e., pirates!
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.
NEW PROGRAMS FOR DOWNLOADS
During the past month, we have added several more programs to the download section in the
new Guest Rooms. So, it is a good idea to be registered on the announcement list
especially to learn about the free goodies we find and offer like the above.To register on
the announcement list, to be notified about more programs and/or articles added to the
Guest Rooms, just click here.
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:
You are encouraged to contribute your thoughts on various subjects to a worldwide audience.
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 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 submissions@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.
To see details of our writing guidelines, please look at: Writing for antenneX
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IN THIS ISSUE
This month is our 101st 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:
Corner
Reflectors Revisited Again |
| LB says about Part 5: "For practical reasons, I shall call any guidance provided by the modeling in this episode less general and more "proof-of-principle" in nature. As we shall see, my model for the driver of the array will only capture some of the essential features, enough to isolate what makes it the key element in expanding the flat-fan dipole driver passband from something over 25% to about 40%. As well, my rod reflector will also differ from the published versions, although it is close enough to replicate the essential ingredients of the original's performance. Finally, I shall by-pass the commercially appropriate procedure of designing to an upper and lower frequency limit, with a resultant mid-frequency. Instead, as with all of the other arrays in this series, I shall design the model for near resonance at 299.7925 MHz, so that 1 wavelength at the design frequency will equal 1 meter. Then, we shall discover where the passband will end in each direction and what the performance will be across the range of frequencies between those limits." |
The Fishing Rod Dipole (FRD) for HF |
| This is the story of an idea Claudio had while shopping at a mall. This is the second similar story situation. The first one generated the “Leash Dipole”, now in the antenneX archives. This time his attention was attracted to some cheap, light and long fishing rods. The cost of each fishing rod was only 8 Euros for a length of 4 m.(each section of 1 m). The material was fibreglass with no carbon load: a good dielectric. The idea is to design a portable, light and cheap HF dipole for field-day use. The development of the design step by step is explained in this article by Claudio. |
Back
to the Off-Center-Fed Antenna |
| Previously, Fred analyzed an off-center-fed antenna and referred to conducting actual field measurements. He finally got to this point and the results are included in this article. Fred analyzed the off-center-fed (OCF) antenna by employing NEC-WIN+ (NW+) and EZNEC+ for Windows (EZW). Radiation patterns and impedance values verses frequency are shown. And Fred compares two configurations. The first is the OCF antenna installed horizontally as a flat top and the second one is with the ends 25 feet above ground. |
Threads
of Lightning |
| Publisher, Jack Stone asked that I organize, in some logical fashion, the recent discussions about lightning protection for a special antenneX article. Jack selected my help since I have a special interest in lightning and lightning protection (as a result of erecting a new tower) and have published a recent series of articles on this very subject. Those articles now reside in the Library and Archives of antenneX. Also, see more about Tom's tower of trouble in the next article. |
Mastering
Masts |
| I never gave more than a few moments’ thought to the choice of an antenna mast, but I should have, as it turned out. antenneX readers may recall that I have a 120-foot tower in my back yard, which used to have two VHF SSB Yagis on top. “Used to” is an important choice of words, here, because those antennas are no longer there. During an ice storm in the first week of January 2005, the mast that held these antennas aloft failed. By “failed” I mean it bent nearly double, whacking the two Yagis against the side of the tower, beating the larger antenna into scrap aluminum and damaging the smaller antenna’s reflector. This is Part 2 of a series that tells my story of Tower woes during a tough winter and my much more thorough research into how best to replace it. |
Performance
of a Small Loop Antenna |
| The performance of a typical small loop antenna is presented at frequencies in the range of 3.6-10.1 MHz. It is argued that the antenna may be reasonably described as small for this range. Measurements of the bandwidth and Q factor are presented, plus direct measurements of the radiated field at various distances and amount of RF input power. Consistency with the Chu bandwidth limit is also demonstrated and described. |
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
September 2005 antenneX Online Issue #101
Send mail to webmaster@antennex.com
with questions or comments.
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Last modified:
December 31, 2010
