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, 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 microprocessors, 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. Most scanners have a weather radio band, allowing the listener to tune into weather radio broadcasts from within 50 miles (or even greater) of a weather radio transmitter.
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 handheld unit is a good idea for optimum performance.
Uniden 200 channel radio scanner |
 
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