The air around you is bursting with radio waves.
You know that you can flip on the AM/FM radio in your car and
receive dozens of stations. You can flip on a CB radio
and receive 40 more. You can flip on a TV and receive
numerous broadcast channels. Cell
phones can send and receive hundreds of frequencies. And
this is just the tip of the radio
spectrum iceberg. Literally tens of thousands of other
radio broadcasts and conversations are zipping past you as you
read this article -- police officers, firefighters, ambulance
drivers, paramedics, sanitation workers, space
shuttle astronauts, race car
drivers, and even babies with their monitors are transmitting
radio waves all around you at this very moment!
To tap into this ocean of electromagnetic dialog and hear
what all of these people are talking about, all you need is a
scanner. A scanner is basically a radio receiver
capable of receiving multiple signals. Generally, scanners
pick up signals in the VHF to UHF range (see How the
Radio Spectrum Works for details on these frequency
Radio scanners are very portable and affordable. In this
edition of HowStuffWorks,
we will look at the basics of scanner operation, examine radio
scanning as a hobby, and show you how to get started listening
to public airwaves you may not have known existed!
Scanners typically operate in
In scan mode, the receiver constantly changes
frequencies in a set order looking for a frequency that has
someone transmitting. Lights or panel-mounted displays show
what channel or frequency is in use as the scanner stops on a
given frequency. The frequencies can be preprogrammed on some
models or manually set on practically all models.
In manual scan mode, the user taps a button or turns
a dial to manually step through preprogrammed frequencies one
frequency at a time.
In search mode, the receiver is set to search
between two sets of frequencies within a given band. This mode
is useful when a user does not know a frequency, but wants to
know what frequencies are active in a given area. If the
frequency the scanner stops at during a search is interesting,
the user can store that frequency in the radio scanner and use
it in scan mode.
Radio scanners can be
either portable, with rechargeable battery
packs, or desktop, like a regular radio. Scanners are gaining
popularity with consumers. With the huge popularity of NASCAR
racing, many people now use scanners at auto racing events
to eavesdrop on the crew-driver communications at races. At a
typical race, there are hundreds of frequencies in use. Each
team has two or three frequencies, while race control, the
sanctioning organization, the medical, fire and track crews
and many others each have assigned frequencies during the
Some of the recently released scanners are capable of
tracking municipalities and police frequencies in the
800-megahertz (MHz) range. This is known as trunk
tracking of computer-controlled trunked radio networks.
Higher-end scanners can be controlled by the serial
port of a personal
computer using special software. This helps the user with
the logging of stations as well as with duplicating the
scanner controls within the software application.
Many models receive the NOAA weather radio broadcasts. This
can be a very useful feature during pending tornados
The controls on a radio scanner can vary, but
practically all of them have:
- Squelch - This is an adjustable control that
keeps the speaker muted (quiet and free from static) when a
station is not transmitting. It works whether the radio is
scanning, searching or manually stepping through stored
frequencies. CB radios also have this control.
- WX button - This is common on some newer models.
This button typically does a mini-scan of some
factory-written frequencies that receive the nation-wide
NOAA weather broadcast reports.
- Numeric keypad - This is used for entering
frequencies or in combination with the "Limit" button, used
for entering upper and lower ranges of a search between two
frequencies. The keypad also lets you enter frequencies
found during a search. More expensive models automatically
store frequencies found during a search.
Buy a copy of "Police Call" (you can get a used one for
next-to-nothing at Amazon.com
or the CD-ROM
version at Radio Shack) to get some frequencies for your
area. See these Frequently
Asked Frequencies, too.
to frequency synthesizers, most scanners can receive
frequency bands in the 29-MHz to 512-MHz range. If you enter
a frequency outside that range, you typically see an error
indication on the display. More expensive models often have
a higher range and often include military aircraft
frequencies. (Earlier scanners did not have numeric keypads
and required the owner to purchase individual crystals
manufactured for a given frequency. Most early scanners only
held six or 10 crystals. The cost of filling up a scanner
with individual channel crystals often approached the cost
of the scanner, much like buying ink cartridges for today’s
low-priced color inkjet
- Search button - This starts the scanner on a
continuous loop between two frequency limits, finding
unknown frequencies within a given range. The searches
typically are in the same automatic increments that the
Federal Communications Commission (FCC) assigns for the
given frequency band being searched. U.S. scanners cannot
search the frequency bands assigned for analog cellular
If you were at a car race, for example, you could do a
search from 460 to 470 MHz and note when the scanner stops
(or look in the race program for assigned frequencies). You
could make a note of the displayed frequency or store it at
that time, and then continue the search. The instruction
manual that comes with a scanner typically shows what
frequency bands are for government, business, aviation, and
- Manual button - This lets the user manually step
through a range of frequencies stored in the scanner. Modern
scanners have 100 to 300 channels for storing frequencies in
the built-in memory. More expensive models have even more.
- Scan button - This starts the scanner on a
continuous loop through all of the frequency banks
(containing stored frequencies). The scanner stops when it
detects a radio signal on a stored frequency; it moves to
the next stored frequency when the radio signal ends. The
user can typically enable or disable certain banks of
frequencies for scanning. Each bank can hold 10 to 30
frequencies, depending on the brand and model of the radio
scanner. Often, banks contain frequencies according to the
type of radio service. Types include emergency, police,
fire, aviation, marine, and business.
- Delay button - This makes the scanner stall for a
short duration on a frequency before moving to the next one.
This delay helps the user hear the other part of the radio
conversation on that frequency.
- Lockout button - This temporarily disables the
radio scanner from stopping on a stored frequency. For
example, you might want to lockout the frequency of a busy
tower at peak travel time during the day when you're
really trying to hear the traffic helicopters
in your area.
Radio scanners usually come with small whip antennas as
well as an external antenna connector. An outside
antenna or attic antenna enables you to hear more
transmissions at a greater distance.
Scanners cannot hear everything. The typical consumer-grade
scanner cannot listen in on 900-MHz cordless
phones that use digital spread spectrum (DSS)
technology. Analog cell phone frequencies are also blocked by
law on all scanners.
law enforcement agencies also use audio inversion and
other scrambling technologies to prevent the reception of
sensitive communications. You will not be able to decipher
CodesYou might hear
the police conversing in the 10-codes.|
Even so, there is an unbelievable number of radio
services that use frequencies most scanners can hear.
Until you buy your own scanner, you can try out scanning
frequencies on Web-controlled
Which Frequencies to Use
Frequency lists are
easy to obtain, often via the Internet. You can find a free
frequency list for your area at this
If you buy a portable scanner, park near an airport
sometime and search the VHF AM aviation-band range, from
approximately 118 MHz to 135.975 MHz, to hear all the activity
that is going on. In some areas, programming 123.45 MHz into
your scanner will let you hear some pilot-to-pilot
Many desktop models work on a 12-volt power supply, so a
cigarette-lighter adapter will allow you to take one on a
Community Service with a Scanner
have helped law enforcement track down criminals. For
Often, family members of those in fire protection,
emergency medical services and law enforcement have a scanner
so they can hear what is going on.
- A scanner listener hears the police conversation about a
recent robbery description, spots the perpetrator’s car and
calls the police to report it.
- A scanner listener hears criminal activity being
discussed on the scanner and reports it to the local police.
Scanner users sometimes receive negative publicity when
they use information that they have heard for private personal
gain. Be sure to obey the scanner laws
Join a neighborhood watch team or a crime watch team and
use the information you hear for awareness and safety.
Listening in via the Internet
If you wish to
get a taste of radio scanning, and have a sound
card in your PC, try the various radio scanner live
broadcasts for police, fire, rail and aviation.
Reception over the Internet may be erratic when there is
network congestion, but this is an inexpensive way to try out
radio scanning via your PC and the Internet.
Once you buy a scanner, read
the manual from cover to cover so you know all of the
capabilities. Ask questions in one of the many scanner
newsgroups on the Internet -- there are active USENET newsgroups
that many scanner hobbyists visit. You can use
rec.radio.scanner or alt.radio.scanner, easily
accessed through your Web browser. Check out some of the scanning
resources on the Internet, then try these tips:
- Become a frequency collector. Start with index cards or
perhaps a small database program on your computer. Learn how
to do searches within a given band -- search a 1-MHz segment
at a time and record the interesting frequencies you find.
- Consider finding a way to run your radio from emergency
power if you have a desktop model. That way, you can
listen to police and fire crews during power failures and
severe weather. Typically, a very small 12-volt battery is
all that is needed.
- Consider storing frequencies of a similar type all in
the same bank. That way, if you just want to listen to
police, fire, or aviation, you can scan just the frequency
memory bank you're interested in and "lockout" the others.
- Take your scanner on a trip and listen from the hotel or
- Take your scanner to all sporting events where radios
- Listen to local amateur radio operators at 144 to 148
MHz. Volunteer ham
radio spotters are often heard during a weather watch or
a weather warning.
For lots more information on radio scanners and related
topics, check out the links on the next page!
Lots More Information!
More Great Links!