February 2010

Folks: The new antenneX online issue #154 for the month of February 2010 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)
Receiving Directivity
A number of years ago, a Ham suggested a somewhat different way of looking at the directivity, one especially applicable to receiving antennas, and--more specifically--receiving antennas designed for the lower HF and upper MF portions of the spectrum. In these regions, amateurs (and others) often use separate receiving antennas, many with very low gain. The goal is not forward gain, but an acceptable signal-to-noise ratio. Many receiving concepts, dating back to the original Beverage antenna, place antennas relatively low to the ground to reduce noise levels. In the process, they sacrifice one of the seemingly holy grails of antenna work, gain. However, these antennas, including the K9AY, the EWE, and others, provide very low-level signals, but even lower noise levels. Since modern receivers tend to have surplus gain, whether inherently or with pre-amplification, the resulting received signal improves its strength over the noise, with resulting improvements in readability.
Despite their low gain, many of the low-band receiving antennas exhibit strikingly good directivity. Conventionally, we might think that one of the available versions of a front-to-back ratio might suffice to characterize the directivity adequately. However, if we review the various front-to-back ideas, we may soon learn why they may not be suitable to the special needs of low-band receiving antennas.
From the Shack By Ian D. Brown, G3TVU
Radio Mobile - What can it do for you?
Part 8 - Route Radio Coverage
We have seen how to perform Radio signal strength Coverage plots from fixed stations in previous parts. Next we found how to ‘Find the Best Sites’ to place a control station to enable it to communicate with other network members or locations. In this part we will explore the ‘Route Radio Coverage’ feature of Radio Mobile.

With this feature a Route will be drawn on the map, and the performance of communication with a moving ‘mobile’ unit explored as it traverses the Route. Application of the Find Best Sites function will then be used to obtain a Base station location capable of providing communications along the Route.

First: Using our previous knowledge of the Object Editor, we will generate a set of waypoints along a Route on a road map. This will be done using zoomed high resolution road maps to accurately place the waypoints at their locations.

Second: The Route Radio Coverage pane will be described, and the Waypoints generated above will be saved as a Route path definition. The radio path performance between the fixed Base station and the mobile moving unit will then be explored along the Route and examined in detail using the Radio Link feature.

Third: Next the Best Sites for ‘Worst Case’ two way communications will be found, and plotted using the generated Route waypoints. Application of the Swap command to see actual signal levels for each direction of transmission is then shown.

Fourth: Expanded views of the Route are generated by using small ‘Step’ intervals. These give more detailed information of signal performance along the Route.

Fifth: Finally Land Coverage data is invoked and the effect of the additional losses on a radio link to a route location shown.

Shortcuts: The program mouse and keyboard shortcuts are then shown in a table.
Ham WorkShop By Martin Steyer, DK7ZB
Simple Building and Tuning of Traps
Traps are useful for multiband operating of all kinds of antennas. It is much easier to build traps as you think and you do not need any special measuring equipment for tuning. Only a transceiver each will be needed and a simple homemade measuring circuit. A trap is a parallel circuit of L and C on the frequency you want to close an antenna segment.

Stone's Throw! By Jack L. Stone, Editor-in Chief & Publisher
A Line of Transmission
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:

A Trap 2-Band 2-Element Beam for 17 and 12 Meters
By L. B. Cebik, W4RNL (SK)

Over the last 2 decades, we have seen a crossroad between older and newer multi-band beam designs. Older multi-band beams tended to make heavy use of traps to achieve 2-band and 3-band performance from a minimum number of elements. Newer beam designs gave up the trap and let each element serve only one primary band, whether the element was a driver or a parasitic element. Initial feed systems, pioneered by Force12, used open-sleeve driver coupling, although later makers have tended toward forms of direct driver coupling. In the market place today, trap and non-trap beams are available both in short and simple and in long and complex designs.

Practical Antennas: Part 2.4
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: Radio Propagation for Beginners
By Robert Gulley, AK3Q

Tuning up and down the dial willy-nilly will always bring in radio signals of some sort simply because there are so many signals out there. Serendipity certainly has its place and its own rewards, but if one wants to get serious about the radio hobby there comes a time when the study of propagation (or how signals get to where they’re going) is a must.

Not only will understanding some basics about propagation make listening opportunities more productive (read “fun”), but it will also allow you to take advantage of special situations where opportunities pop up only for a few minutes or a few hours at best. Catching elusive signals, or even better transmitting under special conditions is a thrill all its own. I'm a newbie at most aspects of this fascinating hobby, so come on and learn along with me!

A No Counterpoise Antenna:
2-Element Vertical Phased Array
By Martin Steyer, DK7ZB

It has been found that the “no counterpoise” antenna presents an easy to match impedance across a very broad range of frequencies with the resistive and reactive components never rising above a few hundred Ohms. Therefore, if feeding these with a twin feed line, then the line losses resulting from high SWR will remain very small, especially when the line length is short as in a typical /p type operation. I therefore decided to see how a pair of vertical “no counterpoise” antennas would cut it when used in a phased array.

More Multi-Band L-pole Vertical Antennas
14 to 29.7MHz Broad-banded and 2-6-10-Meter Multi-band Antennas
By Edward J. Shortridge, W4JOQ

Two previous articles gave a detailed introduction to the "L" broad-banding method, so if you are in doubt about the method, please refer to the previous articles. The last article primarily covered vertical antennas that use dual radiators to simulate a larger diameter single radiator or uses a triangular tower, which actually is a larger diameter radiator. This new article presents 6-10-meter dual-band antennas using a smaller diameter radiator. Additionally, a 2-meter coupled-resonator was added to the 6-10-meter antenna in order to form a tri-band antenna covering the 2-, 6- and 10-meter bands.

Yagi Antenna Insulated Elements Boom Correction
By Dragoslav Dobričić, YU1AW (Serbia)

The boom of Yagi antenna is an inevitable part of its construction. Theoretically and practically, a Yagi antenna can work fine without a boom. A conducting boom is not an intended radiating part of antenna but only an inevitable part of its support construction.

As we know the Yagi antenna can be built in a few ways. It can be built so that elements are insulated and separated by some safe distance from any conducting boom or so that elements pass through boom. The latter method can be done with elements electrically bonded to the boom and elements electrically insulated from the boom. All of these element mounting methods have their mechanical and electrical advantages and disadvantages plus different boom influences to antenna elements.

So far, in several previous articles, we have investigated how the boom dimension, its cross section shape and its distance from antenna elements influence performance of six different 2 m Yagi antennas which are very similar in all characteristics except in Q factor values. In other articles, we have shown how a boom presence influences Yagi antenna performances when elements are insulated and separated by various distances from a conducting boom and finally how the boom influences Yagi antenna performances when elements pass through a metal boom and they are electrically bonded to it. This article investigates the results of correcting yet another unintended consequence of construction as the title implies.

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