Walkie-talkies
Last updated: January 23, 2010.
Do you read me, over? Yes, I read you, over. If you've never had
the pleasure of communicating by walkie-talkie, you don't know how
much fun you've been missing! Before cellphones became popular during
the 1980s and 1990s, walkie-talkies were the most effective way to
share information over short to medium ranges—and they're still
widely used by police officers, military personnel, and the
organizers of public events. What are they and how do they work?
Let's take a closer look!
Photo: A typical low-cost walkie-talkie. This one is a Motorola Talkabout T5720.
Photo by Jhi L. Scott courtesy of US Navy.
What is a walkie-talkie?
Walkie-talkies are handheld, portable radios: they communicate
wirelessly (using radio waves) on a single, shared
frequency band. Each battery-powered unit contains a
transmitter/receiver and antenna (for sending and receiving radio waves), a
loudspeaker that often doubles up as a microphone
when you talk into it, and a button that you "push-to-talk"
(PTT). The loudspeaker/microphone works in much the same way as an
intercom: because a speaker and a microphone contain essentially the
same components (a coil of wire, a magnet, and a paper or plastic cone to pick up or
generate sounds), you can use a single device to do both jobs
essentially by switching the electrical circuit into which it's
connected and reversing the current. More sophisticated walkie-talkies (like the Motorola model shown in our photos) contain
separate loudspeakers and microphones.
How do you use a walkie-talkie?
A group of people who are using walkie-talkies to talk to one another
have to tune in to the same frequency band, which is called a channel.
Their radios are all "receiving,"
so their microphone/loudspeaker units are working as loudspeakers and
probably hissing with static, a bit like a conventional radio
that's not tuned into any particular station.
When someone wants to to talk to the others, they
hold the push-to-talk button on their handset. Their radio goes quiet
as their loudspeaker switches over to a microphone. As they talk into
it, their words are converted into radio waves and beamed out on the
pre-arranged channel (using radio waves typically at a frequency around 460 MHz). Since radio waves
are part of the electromagnetic spectrum, they travel at the speed of
light (300,000 km/second or 186,000 miles/second), so the waves are
picked up almost instantaneously by the other handsets.
The radio waves are converted back into fluctuating electric currents and the
loudspeakers use those to reproduce the sound of the talker's voice. When the
talker has finished, he or she says "over" (meaning my bit of talking
is finished) and releases the push-to-talk button. The radio now
switches back into listening mode and someone else can talk.
Unlike a normal radio, which will only pick up broadcast voices or
music from a radio station, a walkie-talkie is a two-way radio:
you can both talk and listen (send and receive). The main drawback is that
the same frequency channel is used for both things,
so only one person can talk at a time. When
communication devices work this way, they're described as half-duplex (a single channel allows
communication in only one direction at any one time), as opposed to full-duplex (where you
can talk and listen at the same time, as on a telephone).
Photo: This is a typical one-way radio: it will receive things like
music broadcasts from radio stations, but it can't transmit. A walkie-talkie can send and receive,
so it's called a two-way radio.
Advantages and disadvantages of walkie talkies
Pros
Walkie-talkies are robust, easy-to-use, and simple (with
relatively few parts and features), so they're brilliant for use
outdoors and great for children (or
for children who need to stay in touch with parents, for example, on
vacation). They're also great fun: kids love doing the "over" and
"over and out" business. They're very handy in situations where
lots of people need to listen and only one needs to talk at once (for
example, if you're giving instructions to workers on a camp site).
They're extremely convenient, weighing just 100-200g (3.5-7 oz); work
over a decent range (typically 5-10 square km or 2-4 square
miles); and have long battery life (20 hours on 3-4 rechargeable or
alkaline batteries is typical). Walkie-talkies generally have
multiple channels (from about 8 to 25 or more) so you can easily switch to another
frequency if other people are also using walkie-talkies nearby. Some
walkie-talkies can also be used as baby-monitor intercoms.
Cons
Most inexpensive walkie-talkies are analog units, so they're
subject to interference and relatively easy to eavesdrop (more
expensive digital units get around interference, but generally only
military walkie-talkies use encryption). Walkie-talkies are not
designed for communication over longer ranges (for which you'll need
something like CB radio or a cellphone).
