Magnetic Loop RF & You

INTRODUCTION

ecently, a member of our antenna-discussion mail list posted an inquiry about the possible health dangers of RF associated with magnetic loops. Before firing up his new magnetic loop, he wondered if it was safe to TX on HF using 100W with the Loop within a 10-12 foot proximity. Also, he wanted know if it was true that the magnetic RF field is stronger on the lower bands due to the high Q — or was it the same as on the higher bands.

RF exposure and safety for those who live near a commercial or amateur radio station is a highly discussed (or debated) issue. Numerous discussions have been held in the scientific community, the mass media, and other communities for the health effects of Electromagnetic Fields (EMF) caused by high voltage power transmission (50Hz or 60Hz), handset of mobile phone (900 Hz), and the mobile phone transmitting tower.

The magnetic loop antenna is believed by many to have some advantages over others especially as to its more compact size and lack of need for a good ground. For example the questions above came from someone who must operate from a dwelling 30 meters above street level with lots of concrete and steel between his floors.

Shoetsu Miura of Tokyo, Japan and member of the Bio-Electromagnetics Society believes caution should be taken relative to the near field exposure of radiation emitted from magnetic loop antenna. In this regard, he has submitted an article about this subject containing his research and views specifically relative to the magnetic loop antenna.

As with those high-power transmission lines, there is much yet to understand about the effects of exposure to EM and RF on humans or any other living species. No doubt, there will be more articles in antenneX about this subject in the future as research continues.

NEW BOOK RELEASE ON PROPAGATION
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So you have a radio and an antenna, plus all of the other fancy devices imaginable to enable transmit and/or receive signals. But, all of this top-of-the-line radio gear notwithstanding; you wonder why the radio-wave signals behave in such an "unpredictable" manner and you lose contact, or it fades or varies up and down like a roller coaster causing frustration. That's radio wave propagation!

If you don't have a reasonable knowledge of the behavior of propagation, your knowledge of radio has a large hole. This is why we offer this new and fresh approach to learning about this important subject now contained in this series of books, Radio Wave Propagation by M.H. De Canck, ON5AU of Belgium. Volume 1 is now available to be followed by several more volumes.

The author's unique presentation on the subject is not only interesting, but actually makes it a fun learning process. The author's goal is to explain things in a clear and logical manner to everyone wanting to learn, especially for the whole of the radio community — from the beginner to the advanced.

Volume 1 (and the next volumes to follow), provides some bonus study aids, such as: an extra companion 129-page study book with more than 240 illustrations -- a book in its own right, thus two books for the price of one. Also included are 10 of the unique WIZARDS presenting various informative animations to help the reader visualize the propagation properties explained in the Chapters instead of having to, at best, imagine the movements of the propagation phenomenon. Thus, the reader sees, understands and learns faster.

You will be very pleased with this fresh new book on propagation and surprised about the information presented and amazing learning devices not found in other propagation books on the market, making good use of the new electronic media technology not available a few short years ago.

For more info, please go to: http://www.antennex.com/Sshack/prop/prop1.html

NEW ANTENNA-DISCUSSION LIST A SUCCESS!
By now, it should be obvious that the main objective of antenneX is to provide a network of “connections” on a global basis of those who share a common interest in antenna technology and radio-related subjects. This is not only via our main effort, the monthly online magazine, but also through online discussion Forums that we started more than 6-1/2 years ago. Over those years, the number of forums grew to 25 that now store thousands of message postings with valuable reference information.

The purpose of such forums was to provide a convenient “watering hole” for its readers to discuss the various articles in each monthly issue, and/or present other ideas and questions for discussion or debate. While those forums were convenient, they were also easily accessible for vandals and spammers who believe it is their life’s assignment to ruin things for others. Admittedly, the open forums are much more efficient at spreading the “graffiti” than a public bathroom wall.

Another drawback to the above type of forum used was that they were very fragile and subject to breakage of the threads and formatting taking a great deal of time to repair.

In July 2003, it was decided to cap off those forums that had served us well and replace the facilities with a Majordomo managed antenna-discussion list. However, the thousands of messages accumulated by those 25 forums are irreplaceable and too valuable to remove from access by the thousands that visit those forums each month. After all, the information contained never becomes stale as to the fundamentals. We still discuss subjects in this technical field that were first discussed 150 years ago!

Thus, it was decided to retain the previous forums at their present location, but as read-only and without further posts. With so many thousands of postings, a search engine was added to assist in the quick location of messages that mention any subject of interest, or that contain a name of those posting the messages. Just click on the image below to go there.

ONE FORUM CLOSES BUT ANOTHER OPENS
Before capping off the open forums that so many enjoyed for years, we first initiated a new Majordomo managed antenna-discussion mail list, a system with which many are quite familiar. It is a stable system and known to handle lists with 50,000 or more subscribers. Thus, it works quite well for our purpose and, at the same time, lends much more ability to manage the controls necessary to eliminate the drawbacks to an open forum described above.

The Majordomo system contains a daily digest for those who prefer to read from one large email containing all of the individual posts for the day. Also, members can download an entire month’s postings in a single file kept in storage. So, this new Forum can be read in three different formats, and now—a fifth!

WEB-BASED ARCHIVES ADDED
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We are extremely pleased with the success of the Antenna-Discussion List. It has grown much faster than expected. Within a few short months, we have over 600 subscribers to the regular and digest lists and have accumulated nearly 1400 messages about a variety of antenna/radio-related subjects, from a wide spectrum of theories, new & past designs, types of materials, how to choose an antenna for a location, construction techniques, computer modeling, safety such as lightning protection, etc., for big and small antennas.

Some members have urged us to add a Web-Based Archive of the lists. We thought that was a good idea too and thus have provided a Web-Based Archive of all of the past messages for those who had rather read them in that format instead of the daily email "Digest" or single email archive file.

The above struck us as a good idea for others who miss the "old" web forums that we maintained for many years. Essentially, this replaces those forums nicely, except any new postings will have to be through the regular antenna-discussion list. Those postings of course go to all of the members and will show up within 15 minutes or less in the Archives for access and permanent reference.

This new archive includes a powerful search engine to help locate messages by key words such as a term or author's name. Others thought this was a good idea to as more than 150 have registered within the first week!

The previous forums are still available at the same location with its several thousand threads posted over a 6.5+ year period. We have provided a Search tool there as well to help quickly find all of the messages that mention a subject of interest.

Stacking Moxon Rectangles
Part 1: Vertically Stacking Horizontally Oriented Rectangles
By L.B. Cebik, W4RNL

The Moxon rectangle is a 2-element array using dual coupling between elements to produce its nearly cardioidal pattern. Because it depends upon both the mutual coupling between parallel portions of the elements and the coupling between element ends, it is not amenable to the addition of further elements for increased gain. In other words, a Moxon rectangle is not expandable by the addition of director in the manner of a standard Yagi.

Lab Notes: Loops and Their Surface Areas
By Joel C. Hungerford, KB1EGI

During the past few months there has been a lot of discussion about loop antennas in the antenna-discussion reflector at antenneX. A number of unusual questions were asked regarding surface area and skin depth and the effects of wide conductors that have significantly different circumferences on opposite sides of the conductor. This month Joel starts a series of experiments to find the effects of changing the surface area of a loop.

The Balun and Complex Impedance Termination
By Fred M. Griffee, N4FG

There have been numerous instances where a balun (balanced to unbalanced) has been used or felt required. Advertisements abound with recommendations for users of various types of antennas to use a balun to allow equal antenna current distribution. The primary issue has always been concerned with unbalanced to balanced current translation. But there are no known references found concerning balun complex impedance load terminations.

Magnetic Loop Antennas & the Radio Amateur
By Shoetsu Miura, Tokyo Japan

Shoetsu Miura of Tokyo, Japan and member of the Bio-Electromagnetics Society believes caution should be taken relative to the near field exposure of radiation emitted from magnetic loop antenna. In this regard, he has submitted an article about this subject containing his research and views specifically relative to the magnetic loop antenna. As with those high-power transmission lines, there is much yet to understand about the effects of exposure to EM and RF on humans or any other living species. No doubt, there will be more articles in antenneX about this subject in the future as research continues.

Comparing Antennas for Hand-Held Transceivers
Doug Flory ~ WB6BCN

Recently, a friend was telling Doug about his about his new Handi-Talkie. It was a quad band unit, 6 m, 2 m, 70 cm, and 25 cm. They did some field strength measurements using a test antenna on a spectrum analyzer. There are practical limits as what you can achieve with a single band antenna on a walkie-talkie. Some of the concerns involved are not only the physical restraints of your environment, but also the safety to yourself and others.

Stacking Moxon Rectangles Part 2:
Vertically Stacking Vertically Oriented Rectangles
L. B. Cebik, W4RNL

In Part 1, also in this month's issue, we reviewed the situation surrounding the vertical stacking of horizontally oriented Moxon rectangles. Mechanically, this practice is applicable to almost any HF or VHF frequency. However, we discovered that there was a very wide difference between the separation that yields maximum gain and the separation that yields a maximum front-to-back ratio. The maximum gain separation shows a low front-to-back ratio. But, in Part 2, when we turn to vertically oriented Moxon rectangles, we find a much simplified situation.

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. November 2003 antenneX Online Issue #79
reGARDS, Jack L. Stone, Publisher jack@antennex.com