NEW DIRECTIONS RADIO

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Another set of very interesting and useful vibrations exists, not in the air, but in electric and magnetic fields. This "electromagnetic" radiation occurs at frequencies ranging from the audio level up to astronomically high rates.

Some frequencies of electromagnetic radiation can be perceived directly by our bodies. If a device happened to emit radiation at 545,000,000 million cycles per second (megahertz) we would detect the emission as green light. If the frequency were 10,000,000 megahertz, we would feel it as radiant heat.

Most such vibrations, however, are not detected directly by our senses. Ultraviolet (UV) light, X-rays, gamma rays and cosmic rays are all too high in frequency. Other unperceived levels of radiation—which vibrate at a slower rate than light or heat—are the so-called radio frequencies. They're all around us right now, unnoticed.

Figure 1 shows where ham radio fits into this scheme. Note that the various communication services are assigned not just single frequencies but bands of frequencies. The AM broadcast band, for example, extends from 540 kilohertz to 1,600 kilohertz. The stations are spaced at even 10 kHz intervals within these limits, so that there are 106 spots available. (Since the range of a broadcast station is limited, many can be assigned to each frequency without interfering with one another.)

Hams, too, have their own place in the electromagnetic field. In fact, they have more than one: Through some remarkable human foresight (or bureaucratic error), amateurs have been allotted many different bands in various regions of the radio spectrum. Moreover, they're not told—as broadcasters are—to operate on specific frequencies within their territory but are free to move around within prescribed limits.

HOW HAM RADIO WORKS

A ham radio transmitter generates energy at a specific frequency and feeds it to a launching device called an antenna. This mechanism may be simply a wire of appropriate length, 30 or 40 feet above the ground, or a more complex structure of aluminum tubing. In either case, it takes the energy and thrusts it out into space.

What happens then depends upon many factors. If the antenna is simple, the energy heads away from it in straight-line paths and in almost all directions. At frequencies around 100 megahertz (those assigned to FM and TV broadcasting), it almost invariably keeps going in those same paths. Since the earth curves and the people who are to receive the transmission live on its surface, they must not be far away from the source or this line of-sight signal will pass high above them.

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