Radio Waves
Did you ever wonder why the AM numbers on your radio dial are bigger than the FM
numbers? Or what the difference is between regular (VHF) television channels and UHF
channels? Or why you sometimes hear a CB radio in the middle of your favorite rerun? In
fact, what do these things-plus electricity, microwaves, infrared waves, light waves, Xrays, and gamma rays, have in common? All are electromagnetic waves-all of which
travel at the same speed-the speed of light-and each of which vibrates at a constant rate.
DOING THE WAVE
What makes one electromagnetic wave different from another is how fast it's vibrating, or
the frequency (number) of the waves, called cycles, that go by per second. Frequency is
measured in hertz: 1 hertz = 1 cycle per second. Very low frequency waves with long
wavelengths, like electricity (AC power) vibrate at only a few cycles per second; 60 hertz
is common in the United States. Radio waves begin at about 15,000 hertz. Compared to
electricity, that sounds high, but it's nothing compared to X-rays, which vibrate at about
l,000,000,000,000,000,000 cycles per second (10 to the 18th power hertz), or gamma
rays, at more than 10 to the 24th power hertz. Hertz are also referred to in larger, more
easily used units:
1 cycle per second
1,000 hertz
1,000 kilohertz
1,000 megahertz
= 1 hertz (Hz)
= 1 kilohertz (kHz)
= 1 megahertz (MHz) = 1,000,000 hertz
= 1 gigahertz (GHz) = 1,000,000,000 hertz
ON YOUR RADIO
How does this translate to your radio dial? The AM side, usually numbered from 550 to
1600 (some dials remove the last zero, leaving it 55 to 160), stand for kilohertz, although
today's AM band extends from 525 to 1,700 kilohertz, or 525,000 to 1,700,000 cycles per
second. The FM side of your dial is usually numbered from 88 to 108, which stands for
megahertz. FM numbers are lower than AM numbers, but the frequencies are much
higher-88,000,000 to 108,000,000 cycles per second. The FM stations are sandwiched
between television stations, which are assigned frequencies according to channel: VHF
channels 2 through 6 broadcast at 54 to 88 megahertz, below FM frequencies; while
channels 7 to 13 broadcasting at 174 to 216 megahertz, and the UHF channels (14 to 83),
broadcast at 470 to 890 megahertz, are above the FM channels. CB radio uses two bands,
one of which is in 460 to 470 right under the UHF band, which accounts for its
occasional television interference.
WHAT'S THE FREQUENCY KENNETH?
Whatever it's broadcasting, each station is assigned its frequency by the FCC-the Federal
Communications Commission-which has been regulating American broadcasting since
1934, to keep stations from interfering with one other. Each station operates strictly
within its assigned channel, whose size depends on the type of broadcast. AM channels
require only a 10-kilohertz band, while FM channels require closer to 200 kilohertz , and
television channels require 6,000 kilohertz each. So how big is a radio wave? The length
of a wave (cycle) is measured from crest to crest, or from the tip of one wave to the tip of
the next. Very low frequency waves (lower than 30 hertz) can measure over 10,000
yards-more than six miles-from crest to crest. Medium frequency waves-AM
broadcasting waves fall in here-are about 100 to 1,000 yards each. VHF waves-used for
FM and television broadcasting-measure 1 yard to 10 yards. UHF waves are from about a
yard to half an inch. Extremely high frequency waves, such as X-rays, are so small that
they are measured in angstroms (one ten-billionth-0.0000000001-of a meter): light rays
are approximately 3,900 to 7,700 angstroms wide, while an X ray might measure 1
angstrom, and gamma rays can be smaller than 0.000001 angstrom.
LIGHT VS. RADIO
It's the size of the electromagnetic wave, related to its frequency, which is really what
makes a light wave (which you can see) different from and electrical wave, or a radio
wave, or an X ray. The range is phenomenal -- frequencies run from 1 to more than
1 ,000,000,000,000,000,000,000,000,000 to 0.0000000000000001 meter.
Source: Uncle John's Bathroom Reader Plunges Into GREAT LIVES
1. Who is credited with inventing the radio?
2. Why is converting Analog to Digital not an exact science?
3. Give two examples of waves in use in wide area networking
4. Why are waves affected by weather?