Design of a 2-3-El Full-Performance Yagi for Portable & Field Use
with No-Tool Configuration Changing
Part 3: Improving 20- and 17-Meter Performance
By L. B. Cebik, W4RNL (SK)

Parts 1 and 2 described the electrical and mechanical design of a Yagi beam for field and other portable uses. It employed a 12’ boom for high performance from 3 elements on 15, 12, and 10 meters and full 2-element performance on 17 and 20 meters. The maximum element length was 26.33’ to optimize gain and front-to-back ratio on each band. The beam required no matching section, but connected directly to a 50-Ω coaxial cable with 1.6:1 SWR or better.

When using 3 elements, the beam provided a free-space forward gain value of between 6.7 and 7.2 dBi, with a front-to-back ratio of about 20 dB. In contrast, when using only 2 elements (on 17 and 20 meters), the gain dropped to about 6 dBi, with a front-to-back ratio barely over 10 dB. One residual question left by the discussion is whether it might be possible to increase the gain and front-to-back ratio on the lower bands to values more in keeping with those obtained on 15 through 10 meters. Of course, the maximum boom length must remain 12’, and the feedpoint must not require a matching section or network to arrive at a 50-Ω impedance. As well, the individual elements must retain the structure assigned to them in the first two parts of these notes.

Practical Antennas: Part 2.9
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: Monitoring and Scanning Antennas
By Robert Gulley, AK3Q

Inverted L for HF
by Owen Duffy, VK1OD

This article describes a simple Inverted L for the HF bands. The priority requirements were a single antenna system that is unobtrusive and compatible with the Icom AH-4 tuner, reasonable performance on 80m, 40m, and 30m bands and frequency agility.

To achieve reasonable performance down to 80m, the wire needs to be longer than about 35% of a wavelength or 30m. A suitable pair of supports which could accommodate about 27m of wire were identified. With 27m as a starting point, NEC models were created for an Inverted L with a 7.7m vertical section to a suitable anchor point on the mast, and 19m in the horizontal top leg.

The model was examined for reasonable performance down to 80m, and avoidance of high driving impedances in any amateur bands. Although this configuration was fine for the existing HF bands, it resulted in a very high driving voltage in the 5.0 to 5.5MHz region. In the hope that we may get some channels in this area, the top section was reduced to 17.5m to shift the first parallel resonance up to about 6MHz.

The antenna was then constructed and resonances checked against the model for model verification/calibration, and a bulk loss resistance was added to the model to calibrate model results to measured load impedance at the first series resonance.

The New XY-pole Antenna - Part 2
By Edward J. Shortridge, W4JOQ

Part 2 is a continuation of the previous article XY-pole Part 1 (pronounced Zi-pole). Although the previous article presented inexpensive and easy-to-build vertical and horizontal wire antennas, this article will deal mostly with horizontal versions covering the 75-meter amateur radio phone-band from 3.65 to 4.0 MHz

As explained in the previous article, the J-pole antenna is a very narrow-band antenna and is not well-suited to cover even a small portion of the 75-meter band. This article presents the progression from a narrow-band J-pole, to the much broader X-pole antenna, which can cover the entire 75-meter band with a very low SWR. The X-pole utilizes a small capacitor between the quarter-wave matching section, and the end of the radiator, in order to achieve greater bandwidth.

The XY-pole antenna was developed to eliminate the need for a discrete capacitor component and instead uses an overlap of wires from the radiator and the quarter-wavelength matching section to create the same amount of capacitance that might have been used in the X-pole antenna. Using overlapping wires, the XY-pole antenna produces the same SWR bandwidth as the X-pole antenna.

Radial System Design & Efficiency In HF Verticals
By Rudy Severns, N6LF