sending or receiving electromagnetic radiation in the radio frequency range. You probably
know the more common words for this: radio waves. Radio waves are sent from one place to
another without wires.
A radio wave is like two
waves in one: the carrier wave and the signal wave. The radio wave carries signals that
have information in them. This information may be coded onto the wave by interrupting its
transmission at times this is how telegraph works. Or the information is impressed
on the signal by a process called modulation. There are three types of modulation:
amplitude modulation, or AM; frequency modulation, or FM; and pulse (or pulse code)
Radio signals most often contain sound. When sound is
transmitted on radio waves, sound is converted into electric signals by a microphone and
amplified by an amplifier. The signal is then transmitted on a modulated carrier wave the
transmitting machine generates. The modulated carrier wave is also amplified as it goes to
a transmitting antenna. The antenna converts the electric signals to radio waves that go
into the air at the speed of light. Receiving antennas intercept part of the radio wave,
convert it back into electrical signals and feed it to a receiver.
Lets look farther into modulation, amplifiers and
antennas as part of learning how radio waves are sent. Then well see how the antenna
in your stereo makes sounds that you hear as your favorite radio station.
Modulating a radio wave is done when some part of the
carrier wave is made different to match the information-bearing signal wave. The carrier
waves amplitude, frequency or other property is made different.
Earlier we said there are three types of modulation: AM,
FM and pulse. Amplitude modulation means the carrier waves frequency is constant but
its amplitude, or intensity, is changed. In frequency modulation, the amplitude is
constant but the frequency is changed so that the carrier waves frequency is changed
to match another signal (the signal wave). In pulse modulation, the carrier wave is a
series of pulses all the same amplitude, width and equal spacing. Information is
transmitted when pulses in the carrier wave are present or absent.
Weve mentioned "frequency" several times,
so lets look into that more. Radio waves have a property called wavelength, or
frequency. This means the length of the wave is the distance the wave travels from peak to
peak as it goes through the air. A higher frequency has a shorter wavelength. A lower
frequency has a longer wavelength. Transmitting radio waves involves working with
An amplifier controls a signals energy flow to
produce another signal that is similar but has a larger amplitude. An antenna is a system
of wires that transmit or receive radio or other electromagnetic waves. A transmitting
antenna produces electric charges that generate radio waves, which are transmitted through
space. In a receiving antenna, radio waves create a signal detected by an electric
The antenna must match the radio waves frequency so
the signal will be strong.
Once the receiving antenna has separated the signal wave
from the carrier wave, your stereo sends those signals to a loudspeaker, where they are
converted to sound. Thats why if your loudspeakers arent working well, you
dont hear anything, even if everything else has worked right up to now!
Satellites send radio signals.
Cars that link into the Global Positioning System receive radio signals telling the driver
where he is in case hes lost. Your parents car alarm remote sends signals to
unlock or lock the doors with a tiny radio transmitter. To open your garage door, you push
a button on the remote, and a radio signal is sent to your garage, to the radio receiver
in the garage door openers motor housing.
For more information on how the radio spectrum works, link
note about external links
A transmitter sends a modulated carrier wave to the
transmitting antenna. The carrier wave is amplified as it goes to the antenna.
The carrier wave in pulse modulation is a series of pulses
all the same amplitude, width and equal spacing. Carrier wave and signal wave are
together. In this diagram, the carrier wave is represented by white, the signal wave by
A radio wave's frequency relates to the length of the wave,
or the distance the wave is from peak to peak as it travels through the air. Waves have
peaks and valleys. In a close-up look at this diagram, you can see the peaks and valleys
as the radio wave goes from the transmitting antenna to the receiving antenna.