Palstar R30A Owner's Manual page 14

14 Radio Theory Primer
Radio Theory Primer - Frequency and Wavelength
Radio is a way of communicating across distances without the use
of wires by means of electromagnetic waves. These electromag-
netic waves can travel through the Earth's atmosphere, but unlike
sound waves, they are not reliant on the air to carry them. They
travel just as well (or even better) through the vacuum of space.
The most basic characteristic of any electromagnetic wave is its
frequency, which is the rate at which it rises from zero to some
positive level, and then back through zero to some negative level
and then back to zero again. One of these complete alternations is
called a cycle. The number of these cycles occurring each second
is the frequency of the electromagnetic wave. The unit of fre-
quency, the cycle per second, is named after Heinrich Hertz, an
early radio researcher. One Hertz is equal to one cycle per sec-
ond.
Closely related to the frequency of electromagnetic waves is the
characteristic known as wavelength. As a single radio wave or
cycle begins to leave an antenna, it travels outward through
space. How far does it get before one cycle is completed? It trav-
els at the speed of light, 186,000 miles per second, or in Metric
units, 300 million (300,000,000) meters per second. If we were to
radiate a one hertz wave, the front edge of it would have traveled
300 million meters by the time the rear edge of the wave leaves
the antenna one second later. Thus, the wavelength of a one
Hertz transmission would be 300 million meters or 186,000 miles.
long!
If we were to radiate a wave with a frequency of one million Hertz,
one cycle would only take one one-millionth of a second, and the
wavelength would therefore be one one-millionth of 300 million or
300 meters. One million Hertz can be referred to as 1000 kilohertz
(KHz) or 1 megahertz (MHz). 1 MHz is located just about in the
center of the standard AM broadcast band. To calculate the wave-
length of any frequency in meters, simply divide 300 by the fre-
quency in megahertz.
With this explanation of wavelength, you can now understand what
is meant when someone talks about, say, the "80 meter band" or
the "49 meter band." This is just another way to refer to a group of
frequencies that have been set aside for a specific purpose. For
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Electromagnetic Spectrum & Propagation
example, the 80 meter band is an amateur radio (ham) band that
runs from 3.5 MHz to 4.0 MHz. The 49 meter band is assigned to
international shortwave broadcasting and runs from 5.90 MHz to
6.20 MHz.
These meter designations for the bands are chosen to be a nice
round number from somewhere near the middle of the band. The
frequency of an 80 meter wave is 3.75 MHz, the frequency of a 49
meter wave is 6.122 MHz. Obviously, some of the wavelengths in
the band are shorter, and some are longer than the length desig-
nated by the band name.
The Electromagnetic Spectrum
Electromagnetic waves have different characteristics depending
on their frequency. The only difference between radio waves, the
microwaves that cook your food, light beams, and X-rays, is their
frequency. The Palstar R30A receives frequencies in the range of
100 kilohertz (kHz) to 30 megahertz (MHz). Frequencies in the
range of 100 kHz to 300 kHz are called Long Wave (LW). Fre-
quencies in the range of 300 kHz to 2 MHz are called Medium
Wave (MW). Frequencies in the range of 2 MHz to 30 MHz are
called Short Wave (SW) or High Frequency (HF).
At frequencies above 30 MHz (which are higher than those re-
ceived by the Palstar R30), we run into the range of Very High
Frequency (VHF) and Ultra High Frequency (UHF) and beyond.
We will discuss later what you can expect to hear on these differ-
ent frequencies.
Radio Propagation
Propagation refers to the way radio waves travel through the air.
When radio waves leave an antenna, some of them travel close to
the ground. Receivers close to the antenna receive these ground
waves directly. The range of ground waves is limited. The close-
ness of the waves to the Earth means that the Earth absorbs
some of their energy, and farther away from the antenna, the
Earth curves downward, away from the straight-traveling waves,
and the waves pass too high overhead to be received on the
ground. To receive radio waves at longer distances, some other
mechanism is needed.
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