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 Founded in 1988
This online version reaches 214 countries!

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~ January 2012 ~ Monthly Online Issue No. 177 ~

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Read Our Monthly Columns!

Antenna Modeling From The Shack
This was a regular and popular monthly column by L.B. Cebik, W4RNL (SK)Because computerized antenna modeling has become widespread, and its popularity as a design tool continues to increase, this series is devoted to helping readers get the most from the design software used. The articles focus upon the use of NEC and MININEC, along with useful adjunct software as well.

This column is primarily for "Guest Editorials" to provide a podium for our readers to voice their opinions to the rest of the world too. This is a chance for readers to get on their "soapbox" and speak about antenna and radio-related subjects. Don't miss these interesting views about anything and everything about radio and antenna systems! Now, what have YOU to say??

Ham WorkShop

Stone's Throw!

Ham WorkShop, is also another regular monthly column  filled with a variety of "RADIO-STUFF" of value to almost everyone in amateur radio from Novice to Extra and those just beginning to take up this special hobby. This includes subjects, but not limited to: VHF, choosing the right antenna, coax cable, small to mid-scale construction projects in a practical manner, use of test equipment, etc. It is also meant to help readers become more familiar with the technical jargon and the fun side of radio. jls.jpg (2372 bytes)Stone' Throw! a monthly column by antenneX publisher, Jack L. Stone, among other things, is to keep the readers informed about our progress, new developments, plans for the future, and to introduce the authors and their subjects each month. Also, our main slogan around here is "we aim to please", so this serves as a place for the readers to tell the publisher what is wanted or at least make suggestions. Just remember, the publisher is only a Stone's Throw away! Go in for a visit and read this month's column.

Propagation

Antenna Design & Use

marcel.jpg (2142 bytes)Propagation another monthly column by Marcel H. De Canck, ON5AU of Belgium. Signal propagation is a subject that is one of the most basic ingredients of radio and is something everyone in radio should know about in order to maximize communications in the most effective way. It’s not enough to have the best equipment and the best antenna if you are trying to send out a signal against a brick wall. Conversely, one may possess a very crude rig, running low power, but yet transmit/receive a signal to great distances with ease, simply by making use of a thorough knowledge about how signal propagation works within the environment. Follow this column and learn more about propagation! The author of the monthly column Antenna Design & Use is Justin Johnson, G0KSC who does in fact design and install antennas in many parts of the world. He�s a real hands-on expert with years of experience in this field. Following this column will be helpful especially to those pondering a new antenna project. Examples of how to model the designs will appear at times as well. There is something here for just about everyone wishing to know more about how antennas are created, tested and used.

FEATURE ARTICLES THIS MONTH IN THE LIBRARY
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A Power divider / splitter
by Chris Gare

As an alternative to a phasing harness, it's possible to build a 2-way splitter which is a more precise way of matching two 50-Ohm antennas. Also, they can be bought commercially. Justin, G0KSC identified the sizes of box section and tubing to use but I thought it worthwhile checking the size suggestions and this article explains the details of that and construction.

Practical Antennas: Part 5.03
By Marcel H. De Canck, ON5AU

Every transmission line will have some inherent loss, partly of the resistance of the conductors, partly because power is consumed in the dielectric used for insulating the conductors and partly because in many cases a small amount of power escapes from the line by radiation. As transmission lines are made larger by using thicker conductors, the resistance is reduced and as the dielectric material gets closer to low-loss air, the losses are reduced. The skin effect causes current to travel nearer to the surface of the conductors at higher frequencies. Therefore, the effective loss increases as the frequency is increased.

NewcomerNotes ~ It's a New Year!
By Robert Gulley, AK3Q

2011 was an interesting, fun, and frustrating year for me and radio. Interesting because I had the opportunity to experiment with some new antennas, radios, and modes. Fun because (see above!) and because I passed a personal milestone of 100+ DX amateur radio countries. Frustrating because I didn’t get to spend as much time on the air as I wanted (do we ever?!), and because I had some storm damage to antennas which were working quite well before Mother Nature got involved.

Maybe I have equally described your 2011 experiences too (hopefully without the damage!), and like me you are looking forward to 2012. I have a number of projects in mind (always more than I can get to), all of them poised to enhance my enjoyment of this wonderful hobby. I frankly don’t understand people who get bored with radio considering the massive number of things one can hear and do with even a modest setup. No insult intended to those who are finding their interest in radio dwindling; it’s just that I always seem to find new things to challenge me and “old” things to re-discover and thus, new to me.

What is the Role of the Arms of a Linear Broadcast Antenna?
By Kirk T. McDonald, PhD
Professor of Physics
Joseph Henry Laboratories, Princeton University

A broadcast antenna is a transducer of energy from a voltage source into the energy of distanct electromagnetic fields. In its simplest form the antenna should consist of a compact voltage source located in the gap between two linear conductors (the "arms") as shown in a sketch within this paper. We go on to discuss the configuration is substantial detail.

The Self- Resonant Ferrite Rod Antenna - Part 2
By Alan Payne, G3RBJ

A reduction in the length of resonant wire antennas has previously been achieved by placing ferrite beads over the wire. However it is shown here that the ferrite is used more effectively if the wire is wound around the ferrite

HF antennas are normally resonant because their input impedance is then resistive and this easies a potentially difficult matching problem. However resonant HF antennas can be very long and efforts have been made in the past to reduce their length by placing ferrite beads over the wire. For instance Polydoroff (ref 1 p183) measured a 2:1 reduction in the resonant length, using beads with an outside diameter of 3 times that of the wire. A similar experiment was carried out by Grimes (ref 2). However for a given volume of ferrite a much greater reduction in size is possible if the wire is wound around the ferrite, because of the much reduced phase velocity.

The antenna envisaged here is perhaps 2 meters in length with a diameter of 10-15mm, and suitable for HF portable or mobile use. It is self resonant and is therefore unlike conventional ferrite rod antennas, which are tuned with an external capacitor. The design of such an antenna will need to consider a number of parameters, including radiation resistance, bandwidth and efficiency, but it is the ability to self resonate which is covered here.

This is the first part of a two part article
appeared last month, and we continue now in this second part  We started by considering the resonant frequencies of straight wires, and then consider the effects of adding the ferrite.

The DK7ZB-Match for Yagis
By Martin Steyer, DK7ZB

It is a well known phenomenon that the radiators resistance in a Yagi-structure drops down by adding parasitic elements to a dipole as a radiating element. For the VHF-Bands (50-50.5MHz, 144-146MHz, 430-440MHz) a radiation resistance of 25-35Ohm has the best balance for gain, back and side-lobes, bandwidth and SWR at tenable losses in a Yagi.

The classic match for that resistance/impedance is the Gamma-Match. The Beta-Match is a good choice as well, but realisation on VHF is difficult for a homebrew. For that reason a new simple, easy to build match was developed in 1995 for Yagis with resistive loads of 12.5, 18 and 28 Ohms. We present my version in this article.
 


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