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Specialized Mobile Radio (SMR) may be an analog or digital trunked
two-way radio A two-way radio is a radio that can both transmit and receive radio waves (a transceiver), unlike a broadcast receiver which only receives content. It is an audio (sound) transceiver, a transmitter and receiver in one unit, used for bidirecti ...
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.


History

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


Compatibility and purpose

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 Mobile may refer to: Places * Mobile, Alabama, a U.S. port city * Mobile County, Alabama * Mobile, Arizona, a small town near Phoenix, U.S. * Mobile, Newfoundland and Labrador Arts, entertainment, and media Music Groups and labels * Mobile ( ...
or hand-held
walkie talkie A walkie-talkie, more formally known as a handheld transceiver (HT), is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald Hings, radio engineer Alfred J. Gross, ...
radios. One- to five-channel systems may be conventional two-way radio repeaters. More than five channel systems must be trunked.


Fees

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: *Air time (the amount of time any of the user's radio units is talking). *A monthly fee covering site lease costs, engineering, maintenance, and overhead. *Rental of radio units, in some cases.


Conventional two-way radio SMR system

In conventional systems, units are separated into groups by
selective calling In a conventional, analog two-way radio system, a standard radio has ''noise squelch'' or ''carrier squelch'', which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single rad ...
. Radios are usually segmented into customers with each customer on a separate selective calling code. Systems may use
continuous tone-coded squelch system In telecommunications, Continuous Tone-Coded Squelch System or CTCSS is one type of in-band signaling that is used to reduce the annoyance of listening to other users on a shared two-way radio communication channel. (See squelch.) It is sometimes ...
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.


Trunked SMR system

In trunked systems, units are separated into virtual groups by the embedded radio system logic. Channel assignments are controlled by a computer and software. These virtual groups are often referred to as "fleet" and "subfleet" or "talk groups". There is no ''monitor'' function on trunked systems, but users may get busy signals or cryptic overload messages on their radio's display if an attempt is made to transmit while all channels are busy. A service operating an SMR system must maintain a certain number of users for each licensed channel. This is called ''loading''. The service must show adequate loading before licenses for more channels can be granted.


Quality of service

In SMR systems, many factors affect the quality of service. This may include the capacity of the radio system versus the number of radio units using the system. A talkative user community may cause busy signals while a disciplined, professional group of SMR users may keep channels idle. Some systems experience seasonal peaks. For example, a trunked system in an
agricultural Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...
area used by crop harvesting crews may overload and experience busy signals during peaks in harvesting. A system used by a ski resort may overload on a holiday weekend. Disaster planning experts like to say that trunked system users are likely to hear busy signals for the first time when a disaster occurs. A major flood or earthquake is likely to generate a level of call traffic that loads the system to capacity.SMR systems are not designed and built to the same standards as government trunked systems used to manage emergencies. There are many documents addressing this issue. One article discussing this topic is, "Intra- and Inter-County Coordination and Interoperability: Existing Cooperative Agreements," ''Contra Costa County Public Safety Mobile Radio Master Plan, Final Report, June 18, 2002,'' (Fairfax, Virginia: Federal Engineering, Inc., 2002) pp. 25. Siting of the system affects coverage: the system
antennas In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies a ...
should overlook the desired coverage area. Federal Communications Commission regulations require systems using the same radio frequency to be spaced 70 miles from one another or do an engineering study to confirm there will be no interference from closer spacing. Maintenance practices also can affect quality. In some systems, the operator may remove one channel of a trunked system from service to perform repairs. In a heavily used system, this could cause busy signals. Engineering documentation for these systems suggests another evaluation would be ''delivered audio quality''. This is a measurement of the sound quality over all of the involved pieces of communications equipment from end to end. The first clue this may be an issue is that radio users with normal hearing have trouble understanding others when speaking over the radio.


See also

*
Business band In the United States, the business band is the colloquial name used by radio users who utilize, and scanner hobbyists who listen to, the Federal Communications Commission (FCC) Industrial/Business pool frequencies. The regulations listing frequen ...
*
iDEN Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone. It was called the first mobile social network by ma ...
*
Mobile radio Mobile radio or mobiles refer to wireless communications systems and devices which are based on radio frequencies(using commonly UHF or VHF frequencies), and where the path of communications is movable on either end. There are a variety of view ...
**
Professional Mobile Radio Professional mobile radio (also known as private mobile radio (PMR) in the UK) are person-to-person two-way radio voice communications systems which use portable, mobile, base station, and dispatch console radios. PMR radio systems are based on ...
**
Motorola Type I Motorola Type I Is the original type of Motorola's Trunked radio system A trunked radio system is a two-way radio system that uses a control channel to automatically assign frequency channels to groups of user radios. In a traditional half-du ...
trunked radio system A trunked radio system is a two-way radio system that uses a control channel to automatically assign frequency channels to groups of user radios. In a traditional half-duplex land mobile radio system a group of users (a ''talkgroup'') with mobile ...


Notes


External links


FCC definition of Specialized Mobile Radio.FCC PDF file describing US private radio services.
{{Two-way radio Trunked radio systems