February 2008 Issue

Folks: The new antenneX online issue #131 for the month of March 2008 is ready to read at your pleasure!

IN THIS ISSUE
We again include many fine articles by our global writing team. Now, please allow me to introduce this month's line-up of content:

OUR MONTHLY COLUMNS:

Antenna Modeling By L. B. Cebik, W4RNL
Radiation Patterns and Propagation
A number of statements that we might correctly make about the far-field radiation patterns produced by NEC tend to strike a dull chord among newer modelers--if my e-mail over the years has been any kind of indicator. Many of these statements seem to run counter to experience or reports of experience in one or more ways. Most of the answers to the quandaries lie in the realm of distinguishing antenna phenomena as NEC models than from what happens to HF signals as they propagate via the ionosphere toward and from a communications target. Therefore, I shall devote this episode to seeing the differences that are crucial to understanding NEC's reports and communications reports without conflict.

From the Shack By L. B. Cebik, W4RNL
The MFJ-912 (W9IMM) 4:1 HF Balun: Some Preliminary Measurements
Last month, I presented some preliminary measurements of a W2DU-type ferrite bead 4:1 balun that used 50 beads per leg over lengths of RG-62 coax cable. As a partial review of those measurements, the scan-views in this article of the balun with a nearly optimum terminating resistor may serve as a reminder. The scan shows very good results across the 3-30-MHz passband to which I had set the AIM-4170 analyzer. The AIM4170 seemed to be a very good instrument to conduct such preliminary tests. These notes report on the results of the initial tests.

Propagation By Marcel H. de Canck, ON5AU
Space Weather and Solar Properties - Part 3
More than often, I have mentioned in previous issues, and we all know, that the sun is the engine to propagation properties and conditions. The sun’s role in these propagation properties might be in the better or worse sense. With this series of Space Weather and Solar Properties, I shall discuss and explain the impact of the sun on our radio communications. In this first issue, I shall make a start with a brief introduction of some general sun facts and parts of the sun. Later I shall dig more deeply into all of them with the different impacts most solar behaviors might have to our propagation conditions. Once you have insight and knowledge into space weather conditions, you may be able to do some predictions or foresee how propagation may become better or worse. Take one thing for sure; it’s a most violent environment up there!
Stone's Throw! By Jack L. Stone, Publisher
The good, the bad and the useful
A monthly column covering breaking news, new concepts and products, people making news and introduction of the current month's issue articles and its authors—although not limited to this only.

FEATURE ARTICLES IN THE LIBRARY OF NEW ISSUES:

Is COCO Your Cup of Tea?
The Coaxial Collinear Array
By L. B. Cebik, W4RNL

The coaxial-collinear (COCO) array has existed for a very long time. Patents and articles on various forms of the array go back to about 1930. The antenna has aroused considerable amateur interest in the new century as a potential “miracle” high gain, omni-directional antenna for VHF and UHF repeater service. The seeming simplicity of the array, the ready availability of materials, and the promise of easy construction together have yielded dozens of erstwhile copies of the antenna. The question that faces us is whether we really understand how and why the antenna works. Does the coaxial-collinear array really surpass other antenna types in very low-angle radiation strength when placed in vertical VHF service? These notes aim to provide some (but by no means all) of the answers.

Flow of Energy from a Localized Source
in a Uniform Anisotropic Medium
By Kirk T. McDonald, PhD
Joseph Henry Laboratories, Princeton University

Here we want to show the flow of electromagnetic energy far from localized, time-dependent sources in a uniform, linear anisotropic dielectric medium is purely radial, despite the complexity of the wavefronts. Thus, the waves are transverse electromagnetic (TEM) in this region, although the electric displacement D has a longitudinal component in general. This issue is approached by the general methods of geometric optics and acoustics which we consider before making an electromagnetic argument. This paper is a twisting argument to deduce a simple result. Sometimes that's the way it is.

Quados Sector Antenna
for 2.4 GHz WiFi
By Dragoslav Dobričić, YU1AW

After successful construction of the Amos [Amos Antenna, antenneX Issue No. 127 – November 2007] and the Inverted Amos [Inverted Amos Antenna, antenneX Issue No. 130 – February 2008] sector antennas, which are vertically polarized when they are used as sector antennas with wide horizontal and narrow vertical diagrams, I decided to try to construct an antenna with similar performance, but with horizontal polarization. The bi-quad antenna was very interesting as a starting point design and I tried to add more quad elements to get higher gain and narrower vertical diagrams. After some time of computer optimization I found that bi-quad antennas with two more quads added gave a very small increase in gain compared to the original bi-quad antenna, and the expected 3 dB difference is impossible to achieve. Another two quads were added and after optimization, the results showed an even smaller increase in antenna gain than expected. I was convinced that some problem existed and that simply adding quads does not give the expected increase in gain of roughly 3dB with every doubling of element numbers. I expected that the increase in gain will not follow 3dB for system doubling due to lower currents in far quad elements but overall gain was even lower then that expectation. In this article, I explain the solution found to the problem with gain.

Taking AIM: Part 1
By Bob Cerreto, WA1FXT

Over the years I have used a number of different methods to measure unknown impedances at antenna feed points. These methods involved the use of multiple types of test equipment and some set up time. Most methods were difficult to make portable and the data provided by the test equipment sometimes required further calculations. Gathering data at multiple frequencies was very tedious and while the results can be accurate, considerable time is required for project completion. The purchase of an AIM 4170 from Array Solutions has changed our way of performing these types of measurements. We now have a compact, portable and accurate testing method that will provide quick impedance measurements and other electrical parameters.

This multi-part series talks about my experiences with the 4170 and is targeted at the inexperienced user. In this part, initial setup and basic operation will be covered. I shall try not to duplicate detailed information that can be already found in the instruction manual or on the internet. It is hoped that our experiences will serve to reinforce these sources of information and maybe fill in any gaps in a new user’s understanding.

Analysis of Matching Sections
Using Cascaded Transmission Line Stubs
By Jan Gunmar, SM0AQW

Algebraic analyses of transmission line devices are often complicated and unwieldy – it is surprising how so much mathematics can be generated by a few “simple” circuit components – but they can often expose interesting physical properties of the device. This paper gives some examples of algebraic analyses applied to cascaded or “series” transmission line stubs and gives some guidelines for the practical design of matching sections – they are well worth a try!

This paper shows different approaches to deriving equations for practical designs of a “series match.” Hopefully some readers will be inspired to try one or more of the algebraic approaches to their particular matching problems when they want to find out more on “how it works.”

Proplab-Pro 3 - Part 1
By Marcel H. De Canck, ON5AU

At the end of the year 2007, I had a look on the Internet site of STD (Solar Terrestrial Dispatch) and I was happily surprised to find the announcement of their latest release, Proplab-Pro Version 3, released in December 2007. This was the promised “Upgrade” I was expected for many years. In the past I often used Problab-Pro 2 to illustrate and make propagation properties visual in my monthly Propagation column at antenneX. This software packet was not only a program for classical propagation predictions, such as MUF, FOT and Reliability, but in special also a program to analyze the propagation properties of high frequency signals in the ionosphere. This older Version 2 from about 1994 is a DOS related program and has some options not too user friendly, but nevertheless gave reliable results. At the manual of Proplab-Pro 2 was mentioned that these less user-friendly options should be resolved in a future Version 3. The time has come to try out and study the newest release. This series of articles will take the reader on a tour of this new software version and its many features.

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Hope you enjoy the new issue!

Jack L. Stone, Publisher
antenneX Online Magazine
http://www.antennex.com
jack@antennex.com