Scanner (radio)
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 to scan other frequencies when the initial transmission ceases. The terms radio scanner or police scanner generally refer to a communications receiver that is primarily intended for monitoring VHF and UHF landmobile radio systems, as opposed to, say, a receiver used to monitor international shortwave transmissions.
More often than not, these scanners can also tune to different types of modulation as well (AM, FM, WFM, etc). Early scanners were slow, bulky, and expensive. Today, modern microprocessors have enabled scanners to store thousands of channels and monitor hundreds of channels per second. Recent models can follow trunked radio systems and decode APCO-P25 digital transmissions. Both hand held and desktop models are available. Scanners are often used to monitor police, fire and emergency medical services. Radio scanning serves an important role in the fields of journalism and crime investigation, as well as a hobby for many people around the world.
History and use
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, much time could pass between transmissions, while other frequencies might be active. A scanning radio will sequentially monitor multiple programmed channels, or search between user defined frequency limits. The scanner will stop on an active frequency strong enough to break the radio's squelch setting and resume scanning other frequencies when that activity ceases.
Scanners are used by hobbyists railfans, off duty emergency services personnel and reporters.
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 the purchase of 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.
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 programmable scanner's search function. An external antenna for a desktop scanner or an extendable antenna for a hand held unit will provide greater performance than the original equipment antennas provided by manufacturers.
Legal issues
The legality of radio scanners varies considerably between jurisdictions. In the United States it is a federal crime to monitor cellular phone calls. Some US states prohibit the use of a scanner in an automobile. 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, prohibited scanners sold after a certain date from receiving frequencies allocated to the Cellular Radio Service. The law was later 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 analogue technology. There are Canadian and European unblocked versions available, however these are illegal to import into the U.S. Frequencies used by early cordless phones at 43.720--44.480, 46.610--46.930 MHz and 902.000 – 906.000 MHz can be picked up by many scanners. The proliferation of scanners led most cordless phone manufacturers to produce cordless handsets operating on a 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 the operator has a radio license issued from the FCC (Amateur Radio, etc) or the operator's job requires the use of a scanner in a vehicle (ie, Police, Fire, Utilities)
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 convicted of a felony in the last 5 years. 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 the ban),
- 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.
- Licensed Amateur Radio Operators with a valid FCC License may possess Amateur Radio Transceivers capable of reception beyond the Amateur Radio Bands per an FCC Memorandum & Order known as [FCC Docket PR91-36 also known as FCC 93-410]
A partial copy of the Electronic Communications Privacy Act of 1986 can be found here: "Electronic Communications Privacy Act of 1986"
Example laws by country
- United States of America: It is illegal to receive or listen to cellular phone frequencies in the 800 MHz band, to monitor cordless phone calls, or to use information gained from listening to a scanner in furtherance of the commission of a crime. It is also illegal to use for personal gain information obtained from any radio transmissions not intended for public reception, or to disclose such information to a third party. Several states have laws further restricting the use of scanners.
- New Zealand: According to the Act 1989 It is legal to possess and use a scanner at any time to tune to any private voice radio (not encrypted data) provided that private information is not passed on or disclosed to any other person(s) or party(s).
- Australia: It is legal to possess a scanner. It is legal to listen to any transmission that is not classified as telecommunication (i.e. anything not connected to the telephone network).
- Mexico: It is legal to have an unblocked scanner and listen to any radio spectrum frequencies including encrypted and cellular band. According to the Federal Law of General Ways of Communication individuals are prohibited from spreading any information obtained via the mass media.
