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Police radio systems historically used public radio frequencies, and listening to them was, for the most part, legal. Most modern police radio systems switched to encrypted radio systems in the 1990s and 2000s to prevent eavesdroppers from listening in.
A radio band is a small frequency band (a contiguous section of the range of the radio spectrum) in which channels are usually used or set aside for the same purpose. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands.
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.
Shortwave bands are frequency allocations for use within the shortwave radio spectrum (the upper medium frequency [MF] band and all of the high frequency [HF] band). Radio waves in these frequency ranges can be used for very long distance (transcontinental) communication because they can reflect off layers of charged particles in the ionosphere and return to Earth beyond the horizon, a ...
The frequencies used are within the 70-centimeter band, which is currently otherwise reserved for government and amateur radio operations in the United States and most nations worldwide. LPD hand-held radios are authorized for licence-free voice communications use in most of Europe using analog frequency modulation (FM) as part of short range ...
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.
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The term PMR is often used by the public and magazine publishing to refer to the low power (500 milliwatt) PMR446 license exempt radio systems that consist of sixteen FM frequencies between 446.00625 and 446.19375 MHz for analog FM and thirty-two FDMA (digital) channels between 446.003125 and 446.196875 MHz. These are used for personal or ...