A scanner is a radio receiver that automatically tunes, or scans, two or more discrete frequencies. Generally, scanners cover the non-broadcast radio bands between 30 and 950 MHz using FM, although there are models that cover more of the radio spectrum and use other modulation types.
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. The development of the scanner, with its multiple frequencies, allowed the radio to move on to the next frequency after a transmission ended on the first frequency.
Popular amongst hobbyists, reporters, corporate spies, criminals and lawyers alike, 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 used crystals and had only a few programmable channels. Modern scanners allow thousands of frequencies to be stored in various 'memory banks' and can scan at a very fast rate due to modern micro-processors, they even 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.
Frequencies can be found by searching the internet or can be discovered through a radio's search function. An external antenna for a desktop scanner or an extendable antenna for a handheld unit is a good idea for optimum performance.
Legal 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 capable of 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 Congress of the United States (under the pressure of cellular telephone interests) prevented scanners sold in the US from tuning the 800 MHz cellular band. Later, the law was amended to make it impossible to modify radios to receive those frequencies. 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 US. 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 US. The proliferation of scanners led to cordless phone manufacturers going to a much more secure 2.4 GHz system using spread-spectrum technology.
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. Other countries consider possession of a scanner at any time an offense.
External links
Radio Frequency Sources
There are numerous websites which provide lists of frequencies for emergency services and businesses in various areas of the world.
- RadioReference
- Scaning New Zealand
- United States Federal Communications Commission FCC searchable database of licensed radio frequencies