Want of money and the distress of a thief can never be alleged as the cause of his thieving, for many honest people endure greater hardships with fortitude. We must therefore seek the cause elsewhere than in want of money, for that is the miser’s passion, not the thief’s. William Blake (1757–1827), English poet, painter, engraver.


To Catch a Thief
Jack L. Stone, Publisher


INTRODUCTION
The usual platform provided for others to stand on for a soapbox dialogue is to make use of the editorial column, From the Shack. However, this month is my turn to get up on a soapbox about some issues that have caused some changes that affects our visitors/guests. But since my column is also an editorial, I’ll use this vehicle. Please indulge me as I discuss some things encountered in the day-to-day operations of this magazine that I would like to share with my readers. Some of the issues may be familiar and some may not be and so, will be informative to some.

As usual, the behavior of the few makes it a bit more difficult for the many. The Internet is no exception to this behavior and if one wants to enjoy the full benefits of the Internet, it is a good idea to stay informed of the dangers that lurk within. In this regard, I hope what I have to say below will be informative.

To many millions around the globe, the Internet occupies an increasing proportion of time and to some, a very important portion of the day’s activities. This amazing technology has opened up a means of communication available to just about everyone on the planet, even the most remote regions. Perhaps radio is the only other venue that comes close, except it is regulated and requires some sort of permission by regulatory agencies. For the first time, the average folks can communicate with each other across all borders, which is a very good thing. Open communications helps to bypass the information filters that may exist and allows discussions on a one to one basis and defuse propaganda circulated about the people in one country versus another. Knowledge is power!

Anyone with a even so much as a peripheral view of the phenomenal growth enjoyed by the Internet technology knows it has also become a major vehicle for e-commerce as well. For example, I remember when we launched antenneX online; the volume of e-commerce in early 1997 was about $500 million. 5-year projections of multi-billions abounded and were considered staggering, even unbelievable. Well, those projections were indeed, wrong. They were too low!! At least the projections I saw.

Needless to say, such a huge network (web) of potential targets is bound to attract the bad guys like moths to a candle. This is witnessed daily in our emails where the ratio of spam/viruses/worms to total emails has grown from about 8% to nearly 90% within just three years. This is a trend that most have witnessed personally, providing they have been using emails for the past three or more years.

Spamming has become big business and is not likely to stop in the very near future. But, the pendulum always swings and it will be curtailed at the very least as it attracts more and more attention from the lawmakers. However, making laws is only the first step. The important part of making laws is to enforce them before there are any teeth in such laws. For instance, a cry for such a law was made for FAX spams. Well, there are laws now for that, but we still get those faxes!

Moreover, this fight/struggle is an International one and will take the cooperation of big business and governments working together to achieve a working solution. We do hear about the catch and punishment of some of those notorious hackers and malicious virus/worm makers. As we all know by now, punishment alone doesn’t stop crime completely, but at least it is a deterrent to those caught. Of course, there is always another one in line who thinks he/she is smarter than law enforcement and the crime continues.

TRUTH IN COMPUTER SCIENCE
Then, there are misconceptions as to where the junk emails come from. For example, one correspondent from Europe recently said to me:

“…more than 90% of the SPAM comes from IP's inside the USA!…”

Wrong! If one only looks at the last arriving IP, it may appear to be from that country, but usually junk mail is relayed through several different IPs that may be reside in other countries. It really takes some special analysis to determine the real stats and must be at the server side where the trace-back can be conducted and summarized.

Thus, my reply to the 90% “guestimate”:

“....Per your earlier message about the US being the biggest source of SPAM, note this current info from mail server administrators. It might be of help to your reference to this subject in the future in the interest of being factual & true -- just like with any other science."

BTW: I do have my own stats on this directly from the mail server logs which shows every mail relay involved along the route. I haven't checked mine against the 40% but it certainly isn't 90%. Based on what I have seen, the 40% or less applies to my servers....”

Here are the stats I received from one of the mail server administrator reflector — those in the trenches:

“....I don't know where you got that number, but it is completely wrong. The US is the #1 source of spam, but the percentage is around 40%, not 90%.
 
China and  Korea combine for about 25-30%. For the vast majority of non-Chinese, non-Koreans, simply blacklisting ch and kr mail is a very effective way to make a dramatic cull in the amount of spam. I myself don't know anyone in China or Korea who might be sending me mail, for example. This is going to be the case with a large percentage of people.
 
BTW, the US is so high because most US spam is coming from infected Windows machines (zombies). China/Korea spam is coming from ISPs. Simply blocking dynamic IPs and China Korea will probably eliminate 80-90% of the spam hitting an account. It's the final 10% that really starts to take work.....”

It does no good for the cause of a combined effort to fight the junk sources if we just sit around in the vacuum of our personal space and point fingers at other countries creating false rumors and hard feelings about the true sources.

So, it’s left to us as users to find ways to filter out as much of the bad stuff as we can. With the FAX, we can use Call ID to block. With emails we can use filters there too. Unfortunately, no one is conducting the use of those filters and the email system is not nearly as reliable as it was before in its delivery of a message.

There is a mixture of reasons for this breakdown of the email system. On the server side, we have all sorts of methods to apply toward the reduction of junk emails. Unfortunately, there are no “standards.” It’s up to company policy as to how strict or loose the filtering is applied. Sometimes, it may just be up to the server administrator.

On top of the inconsistent application of policies on the server side, then there are the users and their degree of ability and/or diligence in the use of filters within their email programs. Altogether, it is making the email system an “emess!”

On the server side, we must fend off those thieves with special utilities that attempt to scan the server for email addresses. This is just one of the many ways they get your email address, or attempt to. And, one must bear in mind that simply changing your email address is not going to cure the spam problem. The very moment you use that new address, it is subject to harvesting from various techniques employed by the harvesters.

Now, what? Get another email address?? While you may see some initial relief, it’s just a matter of time before that new address starts getting the junk too. So, that’s not the long-term solution—in fact may add to the confusion because many of your legitimate sources may not know about your new email address. Moreover, you have merely shifted the problem to your ISP’s mail server because it must then handle all of the junk arriving to your old email address(es) which continues to soak up bandwidth—and not just for the incoming, but to send back out a notice to the sender that your old box is over quota. At least cancel (or clean out) the old email address if you decide to go with a new one.

If you are concerned about using your most personal email address on the Internet, then simply get an extra one to be used for signups on the Internet from Hotmail or Yahoo, etc. It's easy to do.


COPYRIGHT CONTENT & BANDWIDTH THIEVES
wpe2D.jpg (5717 bytes)Unless you maintain a web site yourself, you may not be aware of this issue: theft of copyright material and bandwidth. Even if you do have a web site, you may not know when this one happens to you. It usually takes some good web log analysis programs to catch this one because at a busy site especially, there are hundreds of thousands of log lines to analyze and summarize the results in a useful manner.

In addition to those email harvesters that are clearly nefarious by intent, here is another method of use, misuse and abuse of valuable bandwidth and copyright content. I’m now referring to those that surf the web and take content of use to their needs without permission and even worse, place the graphics on their sites with link-backs to the original owner’s site. This means every time anyone clicks a page on their site with the link-back graphic, it loads that graphic from the original site—not theirs! The thieves do this knowing they are saving their own bandwidth and the expense of the rightful owner—each and every day!

With a single graphic, it is not too noticeable unless the criminal’s site has a lot of traffic, but this same practice is used for PDF articles where a single article may be several megabytes. That adds up quickly major theft of bandwidth in addition to displaying the article itself without permission. It steals away the valuable bandwidth bought and paid for by the owner for use by his/her visitors/clients/customers and can substantially slow down a server—even bring down the server if the load is severe enough. This is another form of DoS (Denial of Service) although that may not be the original intent of the thief.

BTW: This is also a technique used by the spammers inside their junk messages using HTML. Just as with a web page, they can paste a stolen image in the body of the message. Unwittingly, the owner of the image is hosting the image in each and every one of those thousands of messages sent by the spammer/thief! Ergo, more stolen content and bandwidth when the recipient loads the email containing the image.

Fortunately, there are ways and means to catch this type of theft on the server side, starting with the web stats, which reveals the shameful sources of those deceitful misuses of the property of others. I won’t go into the methods used to stop those misuses, but once caught, the same complex Internet technology can be employed to cut them off. The next time they look at their site with the links, much to their surprise the linked-back images have disappeared and those PDFs now show a “special” page at the end of the link-back. It explains to those innocent visitors to his site that expected to see an article, instead see this page. It explains the situation and at the same time, substantially reduces the unauthorized use and the waste of antenneX’s bandwidth. This is the page. Too harsh….or just desserts??

On one occurrence, after notifying the perpetrator to cease and desist the use of our property, the thief apparently thought he would punish me by posting thumbnails of the images on Yahoo’s cache which contained an option to view the full-sized image, and to email a copy to a friend—with a link-back again to antenneX’s web site. Take a look at what the search will reveal instead—click here: Stolen Property

wpe29.jpg (8937 bytes)Even more disturbing is that this fellow is a Ham, Joe Wojtek Szeliga, SP9P of Poland. Here was his only reply to my request for him to cease and desist (unedited):

To: Jack L. Stone
Subject: Re: Stolen Intellectual Materials
Sorry I forgot to write who is the autor and forgot to ask if I can publisch it on my web page, I never write that I'author. SRI AGN
73, Wojtek SP9P

In contrast to a lame apology of sorts, he did not cease the use of at least three articles found on his web site that belong to antenneX. Inasmuch as he has placed a Copyright 2003 at the bottom of each of those articles, he apparently understands ownership, language barrier or not. Further, the “authors” involved were prominently displayed as always on our version of the article, plus a copyright notice at the bottom of the article. Both were removed when placed on his site.

If he had only asked for permission, I would very likely have given approval to display the selected content as long as it were with the proper credits as prominently displayed in our writing guidelines. But, I doubt that I would have agreed to continue to host the bandwidth for him.

The unauthorized content remains on his site, along with content he has obtained from several others as well with the same link-back use. I don’t know if he obtained their permission or not. Maybe my friends at one of the other “victims”, QRZ will read this and let me know.

I would like to say the one above is the worst example experienced during our 8-year presence online, but it isn’t. However, I believe I have made my point with this example. Ordinarily, I would never reveal the identity of anyone in a situation like this, except his indiscretions are so blatant and defiant, he needs to be identified and placed on “Rogue’s Row” as well.

Ed Note: Just because this "Rogue" is from Poland should not be considered as a reflection in any way on the honorable folks in Poland. In fact, my wife of nearly 20 years was a Pole (1/2 Pole & 1/2 Sicilian) and her father (full-blood Polish immigrant) was a former President of one of the Polish Clubs in NY. Thus, one bad apple does not tarnish my respect for the citizens of Poland.

Of note too, the Holy Father, Pope John is now on the brink of death as I write this (he just lost consciousness). Many consider him one of the greatest Popes of all time. Poland must be very proud. My personal condolences are offered.

We have other fine and honerable readers from Poland. Perhaps one or more of my friends there will volunteer to contact Joe the Rogue and tell him to find another pasttime.wpe2C.jpg (7446 bytes)

The quote I chose this month (at the top) explains this situation quite well as the reason for this one’s theft of the materials may or may not have anything to do with money. The best guess is to fill the site with content the "easy" way in the hopes of generating traffic. The phrase "Build it and they will come" doesn’t work on the Internet.

Postscript: Indeed I know the title I selected this month is the same title used for a book of fiction by David Dodge and published in 1955 by Penguin of London. In that same year, a movie based on this book was released and directed by Alfred Hitchcock, starring Cary Grant and Grace Kelly. But, one cannot possess exclusive rights to a title and so, cannot be subject to copyright.

Okay, enough of that issue for now at least. I’ll step off my soapbox and we’ll just let water seek its own level as far as the final outcome of this issue is concerned. Thanks for your patience while I vented.

NOTE: It should be mentioned that some who have the graphic link-backs may have done it unknowingly. If an image is copied and pasted straight into another web site, it usually will retain the link back to the original site. To check this, just right click the image and look at the "properties" which will show the source of the image.


DOWNLOADS
It is expected that we will be adding more and more content to the download section as we have been concentrating on that project lately. 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, just go here.

NEW OPEN ACCESS GUEST ROOMS BEING BUILT
To reiterate, it is always the few that make things difficult for the many. The relentless attacks on our web site as in the piracy mentioned above has made it necessary to add some 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.

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.

In view of the above, we will be performing a "makeover" of the more than eight free and open-access sections that have always been easily available to all of our friends throughout the many years antenneX has been online. But, we must change with the times as the need dictates.

This pertains to the free access to our new Guest Rooms being built:
• Antenna Science
• Preview Articles
• Software Download
• Antenna Modeling
• From the Shack
• Propagation
• Ham WorkShop
• Stone's Throw!


announce.jpg (43990 bytes)

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!

- - Right at the top is the link for those members that already have a login to go right in.
- - On the left side are the links to the eight different guest rooms.
- - On the right side are links to manage your personal login:
• Get Member Login
• Edit Your Login Info
• Change Password
• Delete Your Login
• Ask for Help

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.


THREE MORE COUNTRIES JOINED LAST MONTH!
Countries number 195, 196 & 197 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 newcomer!


WELCOME SWAZILAND, COUNTRY #195
wpe2F.jpg (10791 bytes)
Background:

Autonomy for the Swazis of southern Africa was guaranteed by the British in the late 19th century; independence was granted in 1968. Student and labor unrest during the 1990s pressured the monarchy (one of the oldest on the continent) to grudgingly allow political reform and greater democracy. Swaziland recently surpassed Botswana as the country with the world's highest known rates of HIV/AIDS infection.

Location:
Southern Africa, between Mozambique and South Africa

Population:
1,169,241 - note: estimates for this country explicitly take into account the effects of excess mortality due to AIDS; this can result in lower life expectancy, higher infant mortality and death rates, lower population and growth rates, and changes in the distribution of population by age and sex than would otherwise be expected (July 2004 est.)

Life expectancy at birth:
Total population: 37.54 years - male: 39.1 years - female: 35.94 years (2004 est.)

Communications:
Telephones - main lines in use: 46,200 (2003)
Telephones - mobile cellular: 88,000 (2003)
Telephone system: general assessment: a somewhat modern but not an advanced system
domestic: system consists of carrier-equipped, open-wire lines and low-capacity, microwave radio relay
international: country code - 268; satellite earth station - 1 Intelsat (Atlantic Ocean)
Radio broadcast stations:
AM 3, FM 2 plus 4 repeaters, short-wave 3 (2001)
Television broadcast stations:
5 plus 7 relay stations (2001)
Internet country code: .sz
Internet hosts: 1,401 (2003)
Internet users: 27,000 (2003)


WELCOME NETHERLAND ANTILLES, COUNTRY #196
wpe1B.jpg (10506 bytes)Background:

Once the center of the Caribbean slave trade, the island of Curacao was hard hit by the abolition of slavery in 1863. Its prosperity (and that of neighboring Aruba) was restored in the early 20th century with the construction of oil refineries to service the newly discovered Venezuelan oil fields. The island of Saint Martin is shared with France; its southern portion is named Sint Maarten and is part of the Netherlands Antilles; its northern portion is called Saint-Martin and is part of Guadeloupe.

Location:
Caribbean, two island groups in the Caribbean Sea - one includes Curacao and Bonaire north of Venezuela; the other is east of the Virgin Islands.

Population:
218,126 (July 2004 est.)

Life expectancy at birth:
Total population: 75.6 years - male: 73.37 years - female: 77.95 years (2004 est.)

Communications:
Telephones - main lines in use: 81,000 (2001)
Telephones - mobile cellular: 81,000 (2001)
Telephone system: general assessment: generally adequate facilities
domestic: extensive interisland microwave radio relay links
international: country code - 599; submarine cables - 2; satellite earth stations - 2 Intelsat (Atlantic Ocean)
Radio broadcast stations:
AM 8, FM 19, short-wave 0 (2004)
Television broadcast stations: 3 (there is also a cable service, which supplies programs received from various US satellite networks and two Venezuelan channels) (2004)
Internet country code: an
Internet hosts: 119 (yr 2001)
Internet users: 2,000 (yr 2000)


WELCOME VIRGIN ISLANDS, COUNTRY #197
Background:
wpe1C.jpg (10684 bytes)During the 17th century, the archipelago was divided into two territorial units, one English and the other Danish. Sugarcane, produced by slave labor, drove the islands' economy during the 18th and early 19th centuries. In 1917, the US purchased the Danish portion, which had been in economic decline since the abolition of slavery in 1848.

Location:
Caribbean, islands between the Caribbean Sea and the North Atlantic Ocean, east of Puerto Rico.

Population:
108,775 (July 2004 est.)

Life expectancy at birth:
Total population: 78.75 years - male: 74.91 years - female: 82.82 years (2004 est.)

Communications:
Telephones - main lines in use: 69,400 (2002)
Telephones - mobile cellular: 41,000 (2002)
Telephone system: general assessment: NA
domestic: modern system with total digital switching, uses fiber-optic cable and microwave radio relay
international: country code - 1-340; submarine cable and satellite communications; satellite earth stations - NA
Radio broadcast stations:
AM 5, FM 11, short-wave 0 (2002)
Television broadcast stations: 2 (2002)
Internet country code: .vi
Internet users: 30,000 (2002)


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.

If you haven’t already joined, you are invited and encouraged to do so. Just click here and follow the instructions on how to join and have fun with the rest of us. If you don't participate—it's a big opportunity lost!

====================================
Antenna Discussion Mail List
JOIN NOW – Click Here
====================================


AN INVITATION TO CONTRIBUTORS
wpe2B.jpg (5748 bytes)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


Subscribe for the Premium Feature Articles!

Enjoy these new concepts with our readership: Be sure your subscription is active so you don't miss these new and exciting concepts and more to follow. If you are thinking about subscribing or renewing, save 21% with the 2-year subscription. Just go to this URL and check on the Subscription option of your choice.
http://www.antennex.com/signup.htm

Keep the issues coming and stay on the leading edge of antenna technology!


~ BE SURE TO VISIT THE SHOPPING SHACK ~
Shipments worldwide ~ plus instant downloads
| Subscription | Books | Software |
Antennas | Components |


IN THIS ISSUE
This month is our 96th online issue online! We again include many fine articles by our great writing team. Now, allow me now to introduce this month's line-up of content:


OUR MONTHLY COLUMNS (plus this one by yours truly):

FEATURE ARTICLES IN THE LIBRARY:

Planar Reflectors Part 4:
Rod or Bar Reflectors
By L.B. Cebik, W4RNL

In the first 3 parts of this study of planar reflectors, we employed wire-grid simulations of closely spaced screens or solid surfaces. Over the life span of planar reflector use, bars or rods have substituted for solid or screen surface. Bars pass the wind easily while having a somewhat better durability than screens, at least in the realm of commercial manufacture. The bars are normally aligned with the dominant polarization of the driving element. For many applications, we would find the bars set horizontally, relative to the earth's surface. However, because anticipated applications of planar reflectors in the 21st century will largely involve services such as the amateur FM repeater system, I have set all drivers vertically. Hence, the bars of a reflector will follow suit.

Wire Discone Antennas, Some Dirty Secrets
By Robert C. Wilson, AL7KK

Discone antennas were first designed at the end of World War II, about 1945 by Armig G. Kandoian. He presented the antenna to communications engineers as having very low SWR (standing wave ratio) properties over a 10-to-1-frequency band in an article in 1946. Information from this article, and Kandoian’s graphs, were copied by a number of popular authors of the period who again presented the discone as being a dream answer to many wide band antenna requirements. Over the years since the original article the discones have been sold to the public in both the solid sheet metal configuration and in rod or wire skeletonized configurations. I decided to mathematically model the skeletonized type of discone antennas to find out for myself how well they should work according to modern math. After doing a significant number of calculations, I feel I must now ask the burning question: Have we been victimized by Kandoian’s wonderful looking flat SWR graphs?

Antenna System Impedance Matching Analysis Including Stubs
By Fred M. Griffee, N4FG (EE Retired)

In two of my previous articles (Article 2 & 3, antenneX Archive VI, #47 & #53), I addressed impedance matching. I shall review some of the areas and include detailed discussion of the series and parallel impedance matching process. Included with this analysis will be stub matching.

The purpose of this investigation is to determine approximate network matching configurations and what might be expected for values. My experience since starting matching analysis demonstrates to me that theory can arrive at a fairly good network component value approximation. From that point on, the needed adjustment change is quite small. This surely removes much of the trial and error tuning (and may eliminate the case where it is thought no match exists at all).

A New Approach to Poynting Vector Synthesis (PVS)
By Claudio Re, I1RFQ & Federico Vavassori

Starting around 1980, some claims of the possibility to generate a new category of antennas was proposed from Hately, Kabbary, Zimmerman, Hart and others. Strangely no one of the proponents were able to put together any mathematical theory or demonstration that can survive to at least a minimal check which is now revisited.

This series of of investigative articles was started by author, Claudio Re. After recognizing that the development of the second configuration proposed involved a very deep mathematical analysis, Re joined with Federico Vavassori, a graduate at the Polytecnic of Milan who developed his thesis on the mathematical analysis of the C-Cube and further development of other “Cubical configurations.“

Add 40 Meters to a 20-Meter Quad
By Dave Cuthbert, WX7G

The other day I was thinking about antennas and as often happens, my thoughts turned to that old stalwart the quad. I thought "Here we have a perfectly good 20-meter loop and although it should make a fine antenna for the 40-meter band, I can't feed it on 40 meters using coax." The problem is that on 40 meters the loop perimeter is a half-wavelength and therefore it presents a high feed point impedance. If we open the midpoint of the loop, so that it forms a bent dipole, it will work fine on 40 meters but then it will present a high feed point impedance on 20 meters. I figured there had to be a way to get the quad to work on both bands.

Need for Balun on Full Wave Loop?
By Dudley Chapman, WA1X

About a month ago there was a discussion controversy on the antenneX antenna-discussion list regarding the need for a balun on coax feeding a full-wave loop. Someone proposed that there was an apparent immunity that the loop had to feedline radiation and perhaps a balun was not needed, or maybe it was even counterproductive. There was a theory floated that perhaps it had something to do with the fact that the loop demanded a balanced current on either side of the feedpoint. Someone ventured a couple of interesting NEC models showing a series of loop and dipole variations where the loop was definitely cleaner than the dipole in regard to feedline radiation.

At that time, I ran a series of models to prove out a theory of mine. My theory is that a loop fed with feedline can have two modes of excitation, where one mode is the circulating currents in the loop, and the other is a linear excitation along the feedline and out onto the loop as a kind of "common mode" excitation.
 

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 2005 antenneX Online Issue #96

Print/Save Article


[../../../copyrigh.htm]