November 2009 Issue

Folks: The new antenneX online issue #151 for the month of November 2009 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 (A Posthumous Publication)
Circular R-X Graphs
The NEC calculation cores produce only a tabular output. Any graphical outputs that we may wish represent post-core-run manipulations of the output data. Most of the work involves finding and parsing the data into a form that a graphing module may use to present the information in a more useful visual manner. Various implementations of NEC provide some of these graphs, namely, the ones most often required or desired by antenna modelers.

Graphs that accompany an implementation of NEC generally come in two forms: polar and rectangular. Polar graphs generally apply to the radiation pattern outputs, since the data values appear in terms of angles and magnitudes. In past episodes, we have examined some of the considerations that go into the forms and plot ring arrangements for such graphs. It is also possible to present these graphs in rectangular form, using the X-axis of the graph for the angular information and the Y-axis for the magnitude. Rectangular graphs are also very useful to present other information, such as the current magnitude and/or phase angle along one or more wires in the model or the resistance, reactance, and SWR information over a specified frequency range.

Some graphical outputs from NEC implementations involve post-core-run calculations. The most common calculation is the SWR relative to a user-selected (or a default) resistive impedance. In addition, some implementations have created polar plots of the left-hand and the right-hand circular components of radiations patterns using calculations based on the radiation pattern data. We have also examined some of these calculations in past episodes.

There is one type of graph that is both very useful and very absent from implementations of NEC. In fact, the only NEC-related program that makes the graph available--to the best of my knowledge at the time of writing--is AC6LA's Multi-NEC. This Excel application does not use a core, but taps into the cores of a number of popular programs for the core run itself. However, Multi-NEC does provide a large collection of facilities unavailable in most NEC implementations.

The graph to which I am referring is the X-Y graph. It is available in many graphing and in most spreadsheet programs. Instead of plotting the magnitude of Y against a progression of set values for the X-axis, the graph plots both X and Y as points on a field. The graphing facility normally calculates the field area needed to contain the points and then creates X- and Y-axes to accommodate the values. Some graphing programs allow the user to modify the axes limits and subdivisions. In addition, most X-Y graphing facilities add a line connecting the successive data points in the series.
From the Shack By Ian D. Brown, G3TVU
Radio Mobile - What can it do for you?
Part 5 - The Radio Link Pane
In the previous parts we have seen how to get started with Radio Mobile, move and resize maps, generate suitable canvases for plots and then perform Polar and Combined Cartesian radio coverage plots.

The Radio Link pane is one of the most powerful and versatile tools available in Radio Mobile, and in this part we will:

First: Explore the Radio Link pane, looking at its features.

Second: Look at the display functions and menus.

Third: Show how the Radio Link control functions work in practice.

Fourth: Examine how to incorporate Land Coverage losses.

Finally: See the Mouse and Keyboard shortcuts for the Radio Link pane.
Ham WorkShop By Robert Cerreto, WA1FXT
A Tower Homemade Lifter for the Lazy Ham
For me, tower climbing has transitioned from an exhilarating adventure to a life-threatening chore. The thrill of the wind blowing through my hair at an altitude has diminished and my hair has fallen out. Despite these age-related milestones, my desire to experiment with antennas has increased even though my desire to climb towers has decreased. So, I needed a way to get some of those beam experiments up into the air without losing my life or injuring somebody else.

My frugal Yankee budget and my well-stocked antenna barn begged me to build a device that would eliminate to danger of tower climbing and allow me to continue meaningful experiments. This device must be relatively inexpensive, safe to use, and allow one person to raise and lower the tower. The tower lifter we are about to discuss may not be appropriate to your needs. However, the materials used and construction techniques used are readily available. You may have to modify the design to fit your tower and available building materials. I am hoping that sharing my experience will inspire you to build a similar device for yourself. I will be here if you wish to ask any questions or share some details about my construction adventure.

Stone's Throw! By Jack L. Stone, Publisher
Measuring RF Power
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:

Designing Multi-Band Parasitic Beams
Part 6: Small Yagi-Yagi Alternatives to the Moxon-Yagi 2-Band Beam
By L. B. Cebik, W4RNL (SK)

The summer VHF DX season held up well through July, and six meters was fairly active even into mid-August, but faded fast after that. I’ll be turning my attention back to the lower frequencies, but have one more installment in this series of articles on VHF gain antennas. In Part 2 of this series we examined a design that emphasized gain somewhat at the expense of other antenna characteristics, especially side and rear rejection. This time we look at one that obtains an excellent overall pattern by balancing forward gain and front-to-rear performance with good SWR bandwidth. Along the way to building this antenna I restored and reused some old parts from my previously disclosed “boulevard of broken beams.”

Practical Antennas: Part 2.1
By Marcel H. De Canck, ON5AU

The ionosphere plays a tricky but an important role to our radio communications, and there is very little we can do about it. But there is plenty you can do about having a good and efficient antenna system. Yes, antenna system, it’s not the antenna itself but the whole part as transmission line, and matching properly the transceiver and the antenna to the transmission line. It is a breath-taking concept that a simple length of wire or rod or tube can transform electrical energy into invisible radio electro-magnetic waves that can cross the space at the speed of light.

How does an antenna system works? Why does the antenna radiate electro-magnetic waves? These questions I heard many times and the answers are not given with few words. Never-the-less, many books and some of great weight and complexity have been written about antennas and many antenna types have been developed and build. Often it is not comprehensive to the layman to fully understand the whys and hows of the radiation capabilities of an antenna and these counts even for the simplest ones like a dipole or a groundplane. Also I often hear many times misconceptions about antenna properties and characteristics. To start with, understanding why and how a simple antenna effective radiates will be explained in a clear view. The dipole is the best antenna to do that and once the secrets of the dipole characteristics and properties are fully understood it will be much easier to have a clear insight of the hows and whys of more complicated antennas.

The first episodes will handle completely about antenna fundamentals mostly with the half wavelength dipole as study example. The dipole is also often a part element of more complicated antennas such as a Yagi and others. In particular for the low frequency bands, the dipole is used by many radio amateurs as transmitting or receiving antenna and its many practical installations and shapes will be fully studied and explained in a chapter later on. In fact many other antenna types will become subject to explanation as the antenna story develops.

NewcomerNotes: Short Wave Listening (SWL)
By Robert Gulley, AK3Q

One of the things which makes the radio hobby so pleasurable for me is how easy it is to find interesting things to listen to on whatever radio happens to be handy. From the cheapest AM-only radio to the fanciest software defined radio and beyond, every listening opportunity holds the potential for something enjoyable with even the smallest effort.

When was the last time you listened to AM radio late at night to hear stations from far away? A local group to which I belong sponsors an informal “ULR” DX Award for folks who snag 10 or 20 states using their ultra-light radios such as the Sony SRF-59 or similar. No one is going to argue ultra-light radios out-perform larger, more robust radios—that’s not the point. What makes attaining the award fun is seeing what can be accomplished with such meager means, and the operant word here is fun! With a radio so light I can forget it is hanging around my neck, stations from hundreds of miles away come in like they were next door. Sure, I can hear more stations and far more distant stations on my Icom or my GE Super Radio II, but listening to the ultra-light definitely has its place. Going in the opposite direction can be just as fun. Find the biggest, oldest, clunkyist radio you can and see what comes over the speaker—chances are you’ll be pleasantly surprised!

Visualizing Antenna Fields
By Ron Nott, K5YNR

The method of visualizing antenna fields as presented here must be categorized as theoretical because as of yet, instruments are not available to provide direct observations. It has been said that the reason mankind has made so much progress in science over the last century is due to learning to make accurate instruments, rather than improved imagination techniques. But the following will require that you exercise your imagination because the instrument to do the observation has not yet been invented. Perhaps your imagination will be challenged into thinking about such an instrument by what follows in this controversial article.

The 6-10 Z-pole Antenna
By Edward J. Shortridge, W4JOQ

Both the 6- and 10-meter bands can be exciting with DX signals that pop up with surprising signal strength. These wonderful DX conditions might not have existed for a long time, but if you want to take advantage when conditions are right, you might consider the following antenna.

A Duel-Band antenna is being presented that covers the 6- and 10-meter bands. Vertical and horizontal versions are considered. Both versions are intended to use moderate size step-diameter aluminum radiators at 10 meters. The vertical version has a radiator that extends from 22 to 39 feet above Average Soil while the horizontal version is mounted at a 30-foot height.

The 6- and 10-meter bands are quite wide and if you might consider a J-pole vertical antenna, you will find it has a very limited SWR bandwidth totally inadequate for use across the entire bandwidths. Additionally, making a J-pole into a duel band antenna might be impossible.

Coaxial Cable Feeder Influence on Four Stacked Yagi Antenna Array
By Dragoslav Dobričić, YU1AW (Serbia)

A previous article series consisted of two parts showing the results of investigating how a coaxial cable antenna feeder influences antenna performance in a situation when minimum and full interaction between antenna and cable is achieved. Investigations were conducted by computer simulations of six different antennas under the same conditions.
In the first part of the previous series, results show a high degree of dependence on cable approaching angle alpha to antenna driven element. This happened despite that the approaching angle alpha was always kept lying in the antenna symmetry plane in order to maintain minimum interaction between cable and antenna. Even under these idealized conditions and in the absence of any other environmental effects, results show considerable antenna performance degradation for some antennas.

In situations when we use a horizontally stacked antenna array, it is simply not possible to have the cable lying in the vertical plane of antenna symmetry. In the second part of the article series, we presented results of investigations conducted on how coaxial cable influences antenna performance when it is not lying in antenna symmetry plane. It is usually used for feeding two horizontally stacked antennas or four antennas stacked two over two, or due to any other reason depending on mechanical support construction demands. In this situation, the cable cannot lie in the antenna symmetry plane, and it is approaching a Yagi antenna’s driver element under some angle beta which is lying in the plane perpendicular to the antenna symmetry plane. In such case, cancelations of some effects were present in a lesser degree and we got more influence than in a situation when the cable was lying exactly in the antenna symmetry plane. In this situation it was also noticeable that coaxial cable became a significant part of the antenna’s radiating structure. Due to significant coaxial cable influence and radiation, antenna radiation diagrams in both planes were considerably distorted.

In this article we will present results of an investigation on how coaxial cable feeder influences four Yagi antennas stacked in an array two over two when cables are arranged in a few different ways.

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Jack L. Stone, Publisher
antenneX Online Magazine
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