Scanner (radio) - History and Use

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, reporters, and criminals.

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 – an early 1976 US entry was the Tennelec MCP-1 – 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 Quick Call type 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.

As radio systems have become more complex, including several different types of trunked radio systems such as Motorola, EDACS, LTR as well as digital, scanners have also become increasingly more complex. This has had the result of reducing access to monitoring public safety communications systems for all but the most hard-core users. The need to know detailed information about how radio systems work is a significant hurdle for the market. Recently, however, database-driven scanners have been introduced that greatly reduce the need for end-users to know the details of the radio systems that they want to monitor. One such model, the Uniden HomePatrol-1, includes the entire database of USA and Canada radio systems from http://www.radioreference.com. All the user needs to do is input their location (typically just their zip code) and the scanner automatically selects the appropriate radio channels for their area. When attached to a GPS receiver, even this requirement is removed, as the scanner will automatically determine it position and continuously update the systems as the user relocates.

Many scanner clubs exist to allow members to share information about frequencies, codes and operations. Most have Internet presence, such as websites, email lists or Web forums. The Southern California Monitoring Association (SCMA), The All Ohio Scanner Club, Chicago Area Radio Monitoring Association (CARMA) and RadioReference.com are examples of these.