Police Radio Scanners
The air around you is bursting with radio waves. You know
that you can turn on your AM/FM radio in your car and
receive dozens of stations. You can flip on a CB radio and
receive 40 more (120 includes single side band units). You
can flip on a TV and receive a lot of broadcast channels.
Cell phones send and receive hundreds of frequencies. And
this is really just the tip of the radio spectrum iceberg.
There are tens of thousands of other radio broadcasts and
conversations are zooming past you as you read this - police
officers, firefighters, ambulance drivers, paramedics,
sanitation workers, space shuttle astronauts, race car
drivers and even railroad conductors are transmitting radio
waves all around you at this very moment!
To tap into this ocean of electromagnetic dialogue 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
What is a Radio Scanner?
A scanner is a radio receiver that can automatically tune, or scan, two or
more discrete frequencies, stopping when it finds a signal on one of them and
then continuing scanning when that frequency goes silent. Generally, scanners
cover the non-broadcast radio bands between 30 and 950 MHz using FM, although
there are models that cover much more of the radio spectrum and use other
modulation types. The traditional use of scanners is to monitor police, fire,
Emergency Medical Services (EMS) and similar radio systems that use a number of
frequencies but with only sporadic use of each.
Radio Scanner History
Scanners developed from earlier tunable and fixed-frequency radios that
received one frequency at a time. Non-broadcast radio systems, such as those
used by public safety agencies, do not transmit continuously. With a radio fixed
on a single frequency, many minutes could pass between signals, while other
frequencies used in the area might be active. The scanning function allows the
radio to progress through a routine of pre-programmed channels, or between two
limits which define a band of frequencies. It will dwell on an active frequency
and will usually resume scanning its defined routine until activity is again
Popular amongst hobbyists, railfans, off duty emergency services personnel,
reporters, corporate spies, criminals and lawyers, scanners allow chosen
frequencies to be stored in memory banks to allow them to be monitored later and
will only stop scanning when there is a signal strong enough to break the
radio's squelch setting.
Scanners first became popular and widely available during CB Radio's heyday in
the 1970s. The first scanners often had between four and ten channels and
required a separate crystal for each frequency received. Modern programmable
scanners allow hundreds or thousands of frequencies to be entered via a keypad
and stored in various 'memory banks' and can scan at a rapid rate due to modern
A hand-held wide band communications receiver. Many recent models will allow
scanning of the specific DCS or CTCSS code used on a specific frequency should
it have multiple users. One memory bank can be assigned to air traffic control,
another can be for local marine communications, and yet another for local police
frequencies. These can be switched on and off depending on the user's
preference. Most scanners have a weather radio band, allowing the listener to
tune into weather radio broadcasts from a NOAA transmitter.
Some scanners are equipped with Fire-Tone out. Fire tone out decodes Quik call
II tones and acts as a pager when the correct sequence of tones is detected.
Active frequencies can be found by searching the internet and frequency
reference books or can be discovered through a radio's search function. An
external antenna for a desktop scanner or an extendable antenna for a hand held
unit is a good idea for optimum performance.
Radio Scanner Legal Use Issues
Radio scanners have had a mixed response from law enforcement agencies and
sometimes championed by those supporting civil liberties. In some communities,
law enforcement has chosen to encrypt their communications. Although scanners
capable of following trunked radio systems and demodulating some digital radio
systems such as APCO Project 25 are available, decryption-capable scanners would
be a violation of United States law and possibly laws of other countries.
A law passed by the Congress of the United States (under the pressure from
cellular telephone interests) prevented scanners sold in the U.S. from tuning
the 800 MHz cellular band. Later, the law was amended to make it illegal to
modify radios to receive those frequencies, and also to sell radios that could
be easily modified to do so. This law remains in effect even though few cellular
subscribers still use analog technology. Typically, there are Canadian and
European "unblocked" versions available, however these are illegal to import
into the U.S. The cordless phone bands at 43.720--44.480, 46.610--46.930 MHz and
902.000 – 906.000 MHz can still be picked up by many scanners. These bands, too,
are illegal to monitor in the U.S. The proliferation of scanners led to cordless
phone manufacturers going to a much more secure 2.4 GHz system using
spread-spectrum technology. Certain states in the U.S., such as New York and
Florida, prohibit the use of scanners in a vehicle unless licensed by the FCC.
In the United Kingdom and France, it is illegal to listen to almost anything
outside the amateur radio and broadcast bands. Canada allows any analog
transmission to be monitored but content of the communication may not be
disclosed. In some parts of the United States, there are extra penalties for the
possession of a scanner during a crime, and some states, such as Michigan, also
prohibit the possession of a scanner in any place by a convicted felon. Other
countries consider possession of a scanner at any time an offense.
In the United States, the general guidelines to follow when using a radio
scanner are that it is illegal to:
- listen in on cellular and cordless phone calls
- intercept encrypted or scrambled communications
- sell or import radio scanners that are capable of receiving cellular
phone frequencies (Note: This rule does not apply to sales by individuals
and radio scanners made before 1985)
- modify radio scanners so that cellular phone frequencies can be received
- use information received for personal gain (A common example is where a
taxi driver listens to a competitor's dispatch channel to steal a customer)
- use information received to aid in the commission of a crime, or
disclose information received to other persons