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

In our exploration of 2-element trap 2-band Yagis, we began a process of sorting out losses due to trap resistance from losses on the lower band due to element shortening. The design exercise also developed a beam, which provided very reasonable performance on a relatively short boom. We measured what counted as reasonable performance by reference both to a sample monoband 2-element driver-reflector Yagi and to relatively well-known trends in this type of Yagi based on long experience and considerable literature. For example, we know that a driver-reflector Yagi reaches its peak value of front-to-back ratio with the elements about 0.125 λ apart. As well, we know that further separation of the elements increases the feedpoint resistance at only very small costs in gain and front-to-back ratio. On this basis, we were able to develop a trap Yagi that allows a direct connection to a 50-Ω transmission line and still performs like a 2-element Yagi.

Practical Antennas: Part 2.5
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 II
By Robert Gulley, AK3Q

The Method of Moments in Electromagnetics
A Contribution by
Massachusetts Institute of Technology

We are pleased to publish this interesting paper based on some lecture notes from MIT. If you are interested in the Method of Moments theories, don't miss this one!

The LC-pole End-fed Vertical Antenna
By Edward J. Shortridge, W4JOQ

The LC-pole antenna consists of a tuned circuit which transforms the 50-Ohm transmission line impedance up to a level that will match the end impedance of a vertical 0.5wL radiator. The tuned circuit does not use taps on it, but instead has the 50-Ohm source in series with a capacitor to the lower high-impedance end of the radiator. The inductor is connected from the radiator end down to the shield of the 50-Ohm coaxial transmission line, thereby giving a DC return path from the radiator to ground via the coax braid and the mast.

This is not a new arrangement for feeding a vertical half-wave radiator, but it is one that is not used to the extent that it could be. Instead, most VHF and UHF home built simple vertical antennas are apt to be the "J-pole" type antenna.

Yagi Antenna Boom Influence on UHF
By Dragoslav Dobričić, YU1AW (Serbia)