Shortwave Antennas Page 6

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Understanding Shortwave Antennas: Page 6

Definitions

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Cycle or Hertz - two changes of the polarity of energy, i.e., stop, forward, stop, reverse, stop.

Kilocycle or kiloHertz (kHz) - One kilocycle = one thousand cycles per second.

Megacycle or MegaHertz (MHz) - One megacycle = one million cycles per second.

Frequency - how frequent something repetitive happens. The frequency of alternating energy is usually expressed in cycles per second or Hertz.

Resonance - Input of alternating or pulsating energy timed to coincide with something’s natural tendency to oscillate. Like pushing a child in a swing - you push at the right time, don’t you? The swing and the child are a resonant pendulum, and you push forward just as the swing starts forward again. The resonance of a guitar string is determined by its length, weight, and tension. The resonance of a quartz crystal is useful as a stable time-base for electronic watches, computers, and radios. A particular length of wire or tubing is resonant at a particular frequency. Longer wires resonate at lower frequencies. Shorter, higher.

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Wavelength - the distance energy travels, at the speed of light, during one complete cycle. Electricity in wire travels a tiny bit slower than light, therefore, a wavelength in wire is not exactly the same as a wavelength in free space (or air).

Bandwidth - how narrow or wide a range of frequencies a particular antenna design can cover efficiently. TV and scanner antennas have a wide bandwidth (hundreds of MHz). A CB antenna has a narrow bandwidth (0.5 MHz). Bandwidth is much more critical when transmitting than when receiving.

Continued…

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