Amateur Radio – Art Or Science ? (Part Three)

The Art of Amateur Radio by Ron Hashiro, AH6RH and the (Emergency Amateur Radio Club) Wireless Dispatch.

This is the last of three articles on the art of amateur radio. In the first article, we took a look at the essence of radio waves. Last month, we looked at the similarity of radio waves and light and looked at ways to use reflections to enhance VHF/UHF radio communications. This month, we examine refraction.

Refraction occurs when a wave passes through materials that vary the speed of propagation. In effect, materials with more or less “densities” will slow down or speed up the wave. This causes the wave front to bend or refract. We see this when light passes from air to glass or from air to water. When the light wave encounters a material that is more “dense” the wave will bend towards the side that first contacts the denser material. The dense material “slows down” that side of the wave, causing the direction of the wave to shift.

An everyday example of this is a magnifying glass. The thick center causes light traveling down the middle to slow for quite a bit before it resumes normal speed, while the light traveling near the edges slow down only for a moment. This causes the waves to bend and come together at a focus.

Radio waves also bend. Recall our discussion that water absorbs and affects radio waves? Variations in water vapor in the air can bend radio waves and plays an important part in a phenomenon called tropo duct openings.

Normally, air temperature continuously decreases as one goes higher in the atmosphere. Occasionally, a weather phenomenon called a temperature inversion occurs that traps a pocket of warm air at higher altitudes. The warm air is sandwiched between two layers of cooler air.

Since warm air can hold more moisture, it has more water vapor than the surrounding cooler, dry air. Radio signals travel slower in the warm, moist air than in the cooler air. This causes the cool air to bend or refract radio signals towards the warmer air. In effect, the two layers of cool air now form a wave guide.

If a strong temperature inversion forms between Hawaii and California, it will form a natural wave guide over 2,000 miles long. This happens occasionally during the summer months of June to August and may last for a few minutes to a few hours. It was especially prevalent during July 1994 when an extra strong high pressure system dumped cool dry air from above and a lack of trade winds caused strong inversions to form below, causing the tropo duct to open for several days.

Another example of bending radio wave called knife-edging occurs near the tops of mountains. If the mountain top has a sharp ridge, the radio wave will bend down as it passes the top of the ridge, away from its original direction. In this setting, an antenna with low gain and a higher angle of radiation would work better than a high gain, low angle antenna.

This effect is especially pronounced and observable along the Koolau ridge line, where the top is often only a couple of feet wide topped with only grass and no trees. Vegetation such as trees and shrubs absorb the signal and ruin the effect. And a narrow ridge line would cause more of the signal to bend without impacting on a broad mountain top.

At the EARC meeting, Bob Hlivak, NH6XO brought out an interesting concept. An old-timer noted to Bob that trans-Koolau propagation is enhanced when there is good cloud cover and diminishes when skies are clear. Apparently, the clouds reflect the signal over the Koolau Mountains more than occurs through the knife-edging effect.

That evening, a quick test between myself and Bev Yuen, AH6NF showed the existence of radio paths that appeared to be enhanced by the complete cloud cover overhead. The signals could not otherwise be explained by the usual knife-edge model. This effect was observed that evening on VHF, and subsequently on UHF. Further tests are being conducted to further explore the concept.

The art of amateur radio seeks to explore and improve our knowledge of radio communications. This series of articles shows that amateur radio is an art built on science with practical applications. QSOs ranging from everyday contacts to critical emergency radio communications can be enhanced by leveraging basic knowledge of radio waves and creatively using any and all available opportunities that surround us in daily life.

I hope you’ll make time to exercise the art of amateur radio and explore the fun world of VHF and UHF simplex radio communications.

Amateur Radio Art Or Science ? (Part Two)

The Art of Amateur Radio by Ron Hashiro, AH6RH and the (Emergency Amateur Radio Club) Wireless Dispatch.

Last month, we took a look at the key element of radio waves…that the major component of a radio wave is really a spreading, magnetic wave and while it may diminish over great distances, it never really disappears. So, let’s see how we can apply what we’ve learned to further our enjoyment of amateur radio.

You might be thinking that radio waves is a kind of black magic that can’t be seen, and therefore can’t be well understood. That’s not really true. If you imaging and look upon radio waves as a kind of light wave, you’ll soon be able to anticipate and predict it’s behavior. It’s so much fun to work directly on simplex, trying out different things, and being amazed when the results are different than what you expected.

If you think of light waves, there are three basic things you can do to with it: radiate, reflect and refract it. The same is true of magnetic or radio waves.

First off, let’s take a look at radiation and the impact of water upon radio waves. The rate that water absorbs radio waves varies with frequency. On the VHF and UHF bands, surrounding vegetation absorbs and affects propagation. Imagine the antenna as a light bulb, and the surrounding plants as a shield blocking your bulb. As you scan around your neighborhood, you can visualize how many plants there are near ground level that affect your “lighthouse view”. Therefore, it is time and money well spent to get an antenna on the roof, or at least above the surrounding plants.

Now, let’s take a look at ways you can reflect radio waves in everyday life. The wavelength of a two meter signal is about six feet. Therefore, if you aim a signal at a suitable object at least six feet square, you can get it to bounce in a new direction. If the object is above you, you can use it to extend your communications range. In effect, it would be the same as if you had moved higher location with a less efficient radio. It can work to your advantage at times.

If you find that a tall building is blocking your signal, you can use it to your advantage. Just go to the other side of the building, and use it as a reflector! The taller the building, the better the reflector. Even if the face of the building is not perfectly aligned with your target, the building features such as windows and railings may reflect enough signal to improve the QSO.

One of my favorite amusements is to use overhead freeway signs to provide a momentary boost in signal. To see how well this works, have another person on simplex that is behind you transmit as you drive under the signs and watch as the signal on your S-meter rise and fall as you pass each sign.

You can amuse your counterpart by letting him/her know that you will predict when your signal strength will increase. The signal reflecting off the sign will be momentarily stronger than the direct signal, and after a while, you’ll get the hang of predicting when the signal will peak. If you use UHF, you can use even smaller objects as suitable reflectors.

Even the mountains that comprise our valley walls can be an asset. Much of our rock is iron-based minerals and can be used to bounce signals out of a valley.

If you can see large, flat objects as mirrors of varying size and quality and view each other’s radios as lanterns, you begin to see all kinds of opportunities around you to bounce radio signals and extend your range. That is part of the art of amateur radio that is built upon science. Next month, we’ll look at refracting radio waves.

Amateur Radio – Art Or Science? (Part One)

The Art of Amateur Radio by Ron Hashiro, AH6RH and the (Emergency Amateur Radio Club) Wireless Dispatch.

Amateur radio is a pastime that is based on science. It is also based on art.

Hard science such as physics, meteorology and chemistry gives us the certainty to explain and comprehend much of how amateur radio works. The “art” comes from seeing things in a new light, blending essential building blocks with intuition and creativity to make new “big picture” applications of amateur radio.

It is when we master and shape each chosen aspect of amateur radio that we go beyond simple nuts-and-bolts technicians to become true artisans and “radio magicians”. Any handbook or textbook will explain the nuts and bolts that we gladly explain, but have you spent a moment to think “outside the box” and grasp a bigger picture?

For example, in a phrase or sentence, how do we generate radio waves? No, the answer isn’t “Put the batteries into the walkie, press on the PTT switch and talk!” To oversimplify, a radio wave is an oscillating variation of a magnetic field. The key points are oscillation, variation and magnetic.

Suppose we had a magnet and could rotate it rapidly. It would cause a variation in the surrounding magnetic field that would be cyclical. That variation would emanate and spread from that magnet. If somehow we could rotate it fast enough, the variation would appear in the usual radio frequencies. We would need to do that thousands or millions of times a second.

Rather than physically spin the magnet, what we would really like to do is to pulse the intensity of the magnet. It’s not practical to physically intensify or diminish a magnet that fast, but we can use the relationship between electricity and magnetism to pulse a magnet electrically. To see this, let’s use an everyday illustration.

Suppose you were at the edge of a pond and had a wooden ball floating on the water attached to a string. What happens as you pull the string up and down in a repetitive fashion? The ball would bounce up and down vertically, and induce horizontal waves that move across the surface of the water.

What happens when the wave hits another wooden ball nearby? The second ball bounces up and down. If we could detect and harness the movement of that second ball, we would have a smaller version of the original motion. The horizontal wave action has been reconverted into vertical motion.

Now, to see the what happens when we transmit through an antenna, view the string as being electricity, the wooden ball as an electron and the disturbed surface of the water as an emanating electromagnetic wave. Like the string, if we attached an RF (radio frequency) generator to a vertical dipole antenna, the moving vertical electric voltage is like the string upon the electric current. It moves electrons (the wooden ball) to create an electromagnetic field that spreads out horizontally from the antenna wire.

As the current grows, the field intensifies, expands and spread out. The essentially magnetic field cuts across neighboring electrical conductors or wires, and like the wave upon the second wooden ball, induces the electrons to move and form a small, minute current in the neighboring wire. And it turns out that the effect works regardless of whether the antenna wire is positioned vertically or horizontally.

The magnetic field can penetrate through many objects as well as be reflected or absorbed by other objects. The importance of this will be discussed in the next article. There is also an electric field that emanates, and it interacts with the magnetic field, exchanging power and restoring equal magnitude to both the electric and magentic fields.

Our jobs as hams is to convert electric current in a vertical piece of wire into horizontal magnetic waves, propagate the waves, and detect it by converting it into vertical electrical current in a second piece of wire. When we amplify that detected current, we have a signal. That is the essence of what we do.

The magnetic wave never really disappears. It may be faint, but it is still present. When the transmitter on the Pioneer spacecraft was shut off last month, it was far beyond the edge of the solar system. The received signal strength was one trillionth of one billionth of a watt and took an array of antennae and receivers to detect it, but it was still present and detectable well below the surrounding noise level.

Incidentally, the above shows that an electron is like a magnet. Since electrons move about in an orbit around the atom nucleus, they exhibit a current which produces magnetism. By using current flow to move the electron, we’ve electrically moved and pulsed a miniature magnet. And we use an oscillating magnetic field to excite or move the electrons to generate radio waves. If you use heat to excite and vibrate the electrons, the emissions show up as light. That’s the key principle behind incandescent light bulbs.

We’ve seen how we use electric current to generate a (magnetic) radio wave, and used the model of the pond to visualize the big picture and see basics of wave generation and propagation. Next month, we’ll look at how we can use this simple model of a radio wave to improve our ability to anticipate and enhance radio communication and thereby add enjoyment to amateur radio.