Radio
Last updated: June 19, 2007.
Free music, news, and chat wherever you
go! Until the Internet came along,
nothing could rival the reach of radio—not even television.
A radio is simply a box of electronic components that snatches passing
radio waves from the air, much like a baseball catcher's mitt, and
turns them back into sounds you can hear.
Radio was first developed in the late-19th century and reached the
height of its
popularity several decades later.
Although it's not quite as popular as it once was, radio remains a
hugely
important form of communication.
In the last few years, it's also become the heart
of such new technologies as wireless
Internet,
cellphones (mobile phones),
and
RFID (radio frequency identification) chips.
Radio waves
Radio is a way of sending electrical energy between two places
without
using wires. That's why it's
often called wireless. The piece of
equipment that sends a
radio wave is called a transmitter; the
radio wave ends its
journey at another piece of equipment called a receiver.
When you pull up the antenna (aerial) on an
ordinary
radio receiver, it catches some of the electromagnetic energy rushing
by.
Tune the radio into a station and an electronic circuit inside the
radio selects only the program you want from all those that are
broadcasting.
How does this happen? The electromagnetic energy, which is a
mixture of electricity and magnetism, travels past you in waves
like
those on the surface of the ocean. These are called radio waves. Like
ocean waves, radio waves have a certain speed, length, and frequency.
The speed is simply how fast the wave travels between two places. The
wavelength is the distance between one crest
(wave peak) and the next,
while the frequency is the number of waves
that arrive each
second.
Frequency is measured with a unit called hertz,
so if seven
waves
arrive in a second, we call that seven hertz (7 Hz). If you've ever
watched ocean waves rolling in to the beach, you'll know they travel
with a
speed of maybe one meter (three feet) per second or so. The wavelength
of ocean
waves tends to be tens of meters or feet, and the frequency is about
one wave every few seconds.
When your radio sits on a bookshelf trying to catch waves coming
into your home, it's a bit like you standing by the beach watching the
breakers rolling in. Radio waves are much
faster, longer, and more frequent than ocean waves, however. Their
wavelength is typically hundreds of meters—so that's the distance
between one wave crest and the next. But their frequency can be in
the millions of hertz—so millions of these waves arrive each
second. If the waves are hundreds of meters long, how can millions of
them arrive
so often? It's simple. Radio waves travel unbelievably fast—at
the
speed of light (300,000 km or 186,000 miles per second).
Analog radio
Ocean waves carry energy by making the
water move up and down. In much the same way, radio waves carry
energy as an invisible, up-and-down movement of electricity and
magnetism. This carries program signals from huge transmitter
antennas, which are connected to the radio station, to the smaller
antenna on your radio set. A program is transmitted by adding it to a
radio wave called a carrier. This process is called modulation.
Sometimes a radio program is added to the carrier in such a way that
the program signal causes fluctuations in the carrier's frequency.
This is called frequency modulation (FM).
Another way of
sending a
radio signal is to make the peaks of the carrier wave bigger or
smaller. Since the size of a wave is called its amplitude, this
process is known as amplitude modulation (AM).
Frequency
modulation
is how FM radio is broadcast; amplitude modulation is the technique
used by AM radio stations.
An example makes this clearer. Suppose
I'm on a rowboat in the ocean pretending to be a radio transmitter
and you're on the shore pretending to be a radio receiver. Let's say
I want to send a distress signal to you. I could rock the boat up and
down quickly in the water to send big waves to you. If there are
already waves traveling past my boat, from the distant ocean to the
shore, my movements are going to make
those existing waves much bigger. In other words, I will be using the
waves passing by as a carrier to send my signal and, because I'll be
changing the height of the waves, I'll be transmitting my signal by
amplitude modulation. Alternatively, instead of moving my boat up and
down, I could put my hand in the water and move it quickly back and
forth. Now I'll make the waves travel more quickly—increasing their
frequency. So, in this case, my signal will travel to you by frequency
modulation.
Sending information by changing the shapes of waves is
an example of an analog process. This means
the information you are trying to
send is
represented by a direct physical change (the water moving up and down
or back and forth more quickly).
The trouble with AM and FM is that the
program signal becomes part of the wave that carries it. So, if
something happens to the wave en-route, part of the signal is likely
to get lost. And if it gets lost, there's no way to get it back
again. Imagine I'm sending my distress signal from the boat to the
shore and a speedboat races in between. The waves it creates will
quickly overwhelm the ones I've made and obliterate the message I'm
trying to
send.
That's why analog radios can sound crackly, especially if you're
listening in a car.
Digital radios can help to solve that
problem.
A brief history of radio
- 1888: German physicist Heinrich Hertz
(1857-1894) made
the first electromagnetic radio waves in his lab.
- 1894: British physicist Sir Oliver Lodge
(1851-1940) sent
the first message using radio waves in Oxford, England.
- 1899: Italian inventor Guglielmo Marconi
(1874-1937) sent
radio waves across the English Channel. By 1901. Marconi had sent radio
waves across the Atlantic, from Cornwall in England to Newfoundland.
- 1906: American engineer Reginald Fessenden
(1866-1932)
became the first person to transmit the human voice using radio waves.
He sent a message 11 miles from a transmitter at Brant Rock,
Massachusetts to ships with radio receivers in the Atlantic Ocean.
- 1906: American engineer Lee De Forest
(1873-1961)
invented the triode (audion) valve, an electronic component that makes
radios smaller and more practical.
This invention earned De Forest the nicknamed "the father of radio."
- 1910: First public radio broadcast made from the Metropolitan
Opera, New York City.
- 1920s: Radio began to evolve into television.
Further Reading
Books you can read
Weightman, Gavin. Signor Marconi's Magic Box.
Cambridge, MA: Da Capo Press, 2003.
Favorite websites
Go shop
