Specialized Mobile Radio

Specialized Mobile Radio (SMR) may be an analog or digital trunked two-way radio system, operated by a service in the VHF, 220, UHF, 700, 800 or 900 MHz bands. Some systems with advanced features are referred to as an Enhanced Specialized Mobile Radio (ESMR). Specialized Mobile Radio is a term defined in US Federal Communications Commission (FCC) regulations. The term is of US regulatory origin but may be used in other regions to describe similar commercial systems which offer a radio communications service to businesses.

SMRs were created when the Federal Communications Commission began to license business and commercial 800 MHz two-way radio systems in the late 1970s.

Any company, such as a taxi service, towing service, or construction company, may use an SMR service. These concerns may rent radios from the SMR operator or may buy compatible radios. SMR systems use differing protocols, frequency ranges, and modulation schemes: not every radio is compatible with every SMR system.

These systems generally consist of one or more repeaters used to maintain communications between a dispatch fleet of mobile or hand-held walkie talkie radios. One- to five-channel systems may be conventional two-way radio repeaters. More than five channel systems must be trunked.

The radio system is operated by a commercial service. Paying a fee allows users to utilize the radio system backbone, increasing their range. Some SMR systems offer telephone interconnect. This allows telephone calls to be made from the mobile radio or walkie talkie. Some systems may also offer selective calling, allowing customers to communicate with individual radios or segments of their entire radio fleet.

Users are charged a fee for some combination of:

In conventional systems, units are separated into groups by selective calling. Radios are usually segmented into customers with each customer on a separate selective calling code. Systems may use continuous tone-coded squelch system for this purpose. A disadvantage is that conventional systems require the user to disable selective calling, (to monitor,) in order to see if another company is talking before using the channel. Conventional systems are usually analog FM.

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