HOME WEB NEWS IMAGES CLASSIFIEDS YELLOW PAGESPOLLS - SURVEYS WIKI COUNTRIES PHOTOS US UK INDIA
Cities Stocks Weather Movies Coupons Travel Blogs Health Horoscope Maps ASIA EUROPE Classifieds Yellow Pages
|
|
|
This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007) |
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 951 MHz using FM, although there are models that cover more of the radio spectrum and use other modulation types. The traditional use of scanners is to monitor police, fire, Emergency Medical Services, and similar radio systems that use a number of frequencies but with only sporadic use of each.
Contents |
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 found.
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 microprocessors.
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 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 by a person who has been convited of a felony in the last 5 years. http://www.legislature.mi.gov/(S(4j5dig3qkwq0hd45waeozviq))/mileg.aspx?page=getObject&objectName=mcl-750-508 Michigan Penal Code, Exerpt 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:
A partial copy of the Electronic Communications Privacy Act of 1986 can be found here: "Electronic Communications Privacy Act of 1986"
| This short section requires expansion. |
| | Electronics Portal |
There are numerous websites which provide lists of frequencies for emergency services and businesses in various areas of the world. These are among the most prominent.
This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia
