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.