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A police code is a brevity code, usually numerical or alphanumerical, used to transmit information between law enforcement over police radio systems in the United States. Examples of police codes include " 10 codes " (such as 10-4 for "okay" or "acknowledged"—sometimes written X4 or X-4), signals, incident codes, response codes , or other ...
The first police radio systems were implemented in Detroit in 1928, when the Detroit Police Department set up a one-way radio system to broadcast crime information to police cars. [2] The frequency was assigned the call sign "KOP" by the Federal Communications Commission .
The police version of ten-codes is officially known as the APCO Project 14 Aural Brevity Code. [ 1 ] The codes, developed during 1937–1940 and expanded in 1974 by the Association of Public-Safety Communications Officials-International (APCO), allow brevity and standardization of message traffic.
MDC (Motorola Data Communications), also known as Stat-Alert, MDC-1200 and MDC-600, is a Motorola two-way radio low-speed data system using audio frequency shift keying, (AFSK).
These frequencies are known as the ISM bands (Industrial Scientific and Medical bands). The return signal of the tag may still cause interference for other radio users. [citation needed] Low-frequency (LF: 125–134.2 kHz and 140–148.5 kHz) (LowFID) tags and high-frequency (HF: 13.56 MHz) (HighFID) tags can be used globally without a license.
Frequencies are reserved for Public Safety and for Industrial users. The 900 MHz band (935-940 MHz) is available solely for Industrial users. Finally, Public Safety entities are allotted an exclusive band of frequencies at 758-806 MHz. Low band has longer range capability, but requires mobile antennas as long as nine feet (2.7 m) tall.
In the Americas (defined as International Telecommunication Union (ITU) region 2), the FM broadcast band consists of 101 channels, each 200 kHz wide, in the frequency range from 87.8 to 108.0 MHz, with "center frequencies" running from 87.9 MHz to 107.9 MHz. For most purposes an FM station is associated with its center frequency.
This provides the receiver with a list of frequencies that allows a receiver to re-tune to a different frequency providing the same station when the first signal becomes too weak (e.g., when moving out of range). Before performing the switch, a radio will check for a matching PI code to ensure the AF is the same station.