Why? Why? Why? A Basic Tri-Band Yagi
By L. B. Cebik, W4RNL (SK)

The design of multi-band HF Yagis is as much an art as a science. I have the utmost admiration for those who design these antennas. The following notes do not compete with their work, but might be considered an homage to their continuing efforts to improve the performance that we can wrest from a multi-band array. We shall examine the design of a tri-band Yagi of very modest proportions for 20 through 10 meters with seven elements on a 13’ boom (make it 14’ to include the mounting hardware).

Why #1: I receive e-mails and letters asking why there are no such beams currently at my web site. This set of notes is my general answer.

Why #2: Even using the best materials available, the cost for a knowledgeable builder will be between 1/3 to ½ the cost of a commercial beam with the same general capabilities.

Why #3: For the newer antenna addict, looking at a tri-band design provides a chance to see some of the challenges that go into such designs.

The “why” terms are actually a code name for the design, which I have designated for my own files as YYY-TRI-15-70-MD. The file name breaks down this way. YYY means that the beam consists of three Yagis interlaced acceptably: 2 elements for 20, 2 elements for 15, and 3 elements for 10.

Practical Antennas: Part 2.3
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: Small Magnetic Loop Antennas
By Robert Gulley, AK3Q

THE Moxon Beam
By Martin Steyer, DK7ZB

The Moxon Beam was introduced by L. Moxon (G6XN) in his book "HF Antennas for all Locations" (RSGB- Publications, Great Britain 1993). This beam is a 2-Element-Yagi with radiator and reflector and reduced size to about 75% of a normal beam. The 2-Element-Yagi with reflector has normally a 0,2-l-boom and an impedance of 50 W. The Moxon-beam has a 0,18-l-boom and still 50 W. This is good impedance for wire beams. The ends of the two elements are bent backward (radiator) or forward (reflector) and act as a capacitive load. That is much better than inductive loading with coils. So we have greater bandwidth and lower losses. Through the reduced size we get a 0,5-0,7 dB lower gain than with a full-size beam.

Multi-Band L-pole Vertical Antennas
14 to 29.7MHz Broad-Banded Antennas
By Edward J. Shortridge, W4JOQ

This "Multi-Band L-pole Vertical Antennas" article is a continuation of my previous article, entitled "6-10-meter & 10-20-meter L-pole Antennas, which was published in the antenneX issue No. 152 of December 2009. This previous article gave a detailed introduction to the "L" broadbanding method, but it only covered horizontal antennas. This new article takes up where the other one ended and presents a variety of vertical configurations covering the entire frequency range from 14 to 29.7 MHz. All of the antennas presented utilize two radiators in order to simulate a larger diameter. For improved SWR across this band, a version is shown which uses a lightweight triangular aluminum tower normally used for meteorological purposes, this tower will be used as the radiating element, and will be fed in its center.

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