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Notes on 2-Band (2-M, 70-CM) LPDAs
Part 1. Narrow-Band LPDAs
By L. B. Cebik, W4RNL
(A Posthumous Publication)

The amateur 2-meter and 70-centimeter bands have an approximate 3:1 frequency ratio. On both bands, FM repeaters use the upper portion of the bands, so the ratio is more exact. For example, the 3rd harmonic of 146.7 MHz is about 440 MHz. FM repeater services use vertically polarized antennas on both bands. Therefore, the idea of a single antenna to cover the FM repeater portions of both bands naturally arises.

It is possible to use a ½-λ dipole element in the 3/2-λ mode to provide dual band coverage. The advantage of this strategy is that the impedance on both frequencies will be relatively low. However, as we increase the mode of use, the self-resonant impedance does increase. As well, because a 3/2-λ center-fed element has only two ends—and hence, only two end-effect regions—the ratio of self-resonant frequencies tends to be slightly higher than 3:1.

One way to overcome these potential limitations is to use one or another form of wide-band technology. The most common form is to create a log-periodic dipole array (LPDA) for the lower frequency region and then to operate the array on the upper band as well. These notes examine the practice as commonly implemented and then with improvements. In this part, we shall look at a minimalist design intended to cover only the amateur band at 2 meters and the FM portion of the 70-cm band.

Momentum in a DC Circuit
By Kirk T. McDonald, PhD
Joseph Henry Laboratories, Princeton University

We discuss the electromagnetic and mechanical momentum in a DC current loop of resistance R that is powered by battery of voltage V. Because the loop is at rest in the laboratory, its total momentum should be zero. However, a DC current loop is a dynamical system and that its electrical resistance R causes dissipation of power at the rate V²/R= VI = I²R, where the DC current I is, of course, I = V/R.  This power flows from the battery to the loop in a manner first well described by Poynting. As shown in a diagram by Poynting in this article, the power does not flow down the wire of the loop, but rather it flows through the air/vacuum and enters the wire at right angles to its surface.

Performances of Wet Yagi Antennas
By Dragoslav Dobričić, YU1AW

Reviewing the TAK-tenna: Part 1
By Dave Cuthbert, WX7G

In this Part 1 of my review, we’ll explore the theoretical aspects of this antenna and small dipoles in general. In Part 2, we’ll fire up the TAK-tenna and see how it performs on the air, how to get the most out of it, and how to multiband it, and most importantly of all, how it works.

The Double Slit Puzzle
Quantum or Classical?
By William C. Miller, KT4YE

Charles Augusta Young1 (1834-1908), professor of astronomy at Princeton University (1877-1905), first accomplished the Double Slit experiment in the first decade of the 19th century. It was inspired by earlier experiments using water to investigate wave performance. His experiment was designed to test whether light was composed of waves or particles. The results were similar to those obtained with water, and showed that light is a wave phenomenon. Later tests showed that the Double Slit experiment also opened the door to a remarkable puzzle. A solution to this puzzle led us to the enigmatic world of Quantum Mechanics.

At first glance, this physics experiment seems to have nothing at all to do with antennas. However, as we shall see, there is a possibility that a well-known antenna configuration — the slot antenna — explains the puzzle without the need for Quantum Mechanics!

Magnetic loop automatic tuner
By Anselmo Stiffan