Mobile Radio
Encyclopedia
This article is about professional equipment. For mobile radios used in amateur radioAmateur radioAmateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
, see amateur radio mobile operation.
Mobile radio or mobiles refer to wireless communications systems and devices which are based on radio frequencies, and where the path of communications is movable on either end. There are a variety of views about what constitutes mobile equipment. For US licensing purposes, mobiles may include hand-carried
Walkie-talkie
A walkie-talkie is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald L. Hings, radio engineer Alfred J. Gross, and engineering teams at Motorola...
, (sometimes called portable), equipment. An obsolete term is radiophone.
A sales person or radio repair shop would understand the word mobile to mean vehicle-mounted: a transmitter-receiver (transceiver) used for radio communications from a vehicle. Mobile radios are mounted to a motor vehicle usually with the microphone and control panel in reach of the driver. In the US, such a device is typically powered by the host vehicle's 12 volt electrical system.
Some mobile radios are mounted in aircraft, (aeronautical mobile), shipboard, (maritime mobile), on motorcycles, or railroad locomotives. Power may vary with each platform. For example, a mobile radio installed in a locomotive would run off of 72- or 30-volt DC power. A large ship with 117V AC power might have a base station
Base station
The term base station can be used in the context of land surveying and wireless communications.- Land surveying :In the context of external land surveying, a base station is a GPS receiver at an accurately-known fixed location which is used to derive correction information for nearby portable GPS...
mounted on the ship's bridge.
Disambiguation: Two-way versus telephone
The distinction between radiotelephonesRadiotelephone
A radiotelephone is a communications system for transmission of speech over radio. Radiotelephone systems are not necessarily interconnected with the public "land line" telephone network. "Radiotelephone" is often used to describe the usage of radio spectrum where it is important to distinguish the...
and two-way radio
Two-way radio
A two-way radio is a radio that can both transmit and receive , unlike a broadcast receiver which only receives content. The term refers to a personal radio transceiver that allows the operator to have a two-way conversation with other similar radios operating on the same radio frequency...
is becoming blurred as the two technologies merge. The backbone or infrastructure supporting the system defines which category or taxonomy applies. A parallel to this concept is the convergence of computing and telephones.
Radiotelephones are full-duplex (simultaneous talk and listen), circuit switched, and primarily communicate with telephones connected to the public switched telephone network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
. The connection sets up based on the user dialing. The connection is taken down when the end button is pressed. They run on telephony-based infrastructure such as AMPS
Advanced Mobile Phone System
Advanced Mobile Phone System was an analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1983, Israel in 1986, and Australia in 1987. It was the primary analog mobile phone system in North America through the 1980s and into the 2000s...
or GSM.
Two-way radio is primarily a dispatch
Dispatch (logistics)
Dispatch is a procedure for assigning employees or vehicles to customers. Industries that dispatch include taxicabs, couriers, emergency services, as well as home and commercial services such as maid services, plumbing, HVAC, pest control and electricians.With vehicle dispatching, clients are...
tool intended to communicate in simplex or half-duplex modes using push-to-talk, and primarily intended to communicate with other radios rather than telephones. These systems run on push-to-talk-based infrastructure such as Nextel's iDEN
Iden
For other uses of the word, see Iden The Iden was an English automobile manufactured from 1904 until 1907. Designed by George Iden, formerly of Daimler, they were four-cylinder 10/17 hp and 25/35 hp shaft-driven cars; each came with "Idens's frictionless radial gearbox"....
, Specialized Mobile Radio (SMR), MPT-1327
MPT-1327
MPT 1327 is an industry standard for trunked radio communications networks.First published in January 1988 by the British Radiocommunications Agency, and is primarily used in the United Kingdom, Europe, South Africa, New Zealand, Australia and even China...
, Enhanced Specialized Mobile Radio (ESMR) or conventional two-way systems. Certain modern two-way radio systems may have full-duplex telephone capability.
History
Early users of mobile radio equipment included transportation and government. These systems used one-way broadcastingBroadcasting
Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...
instead of two-way conversations. Railroads used medium frequency range (MF
Medium frequency
Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...
) communications (similar to the AM broadcast band) to improve safety. Instead of hanging out of a locomotive
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
cab and grabbing train orders while rolling past a station, voice communications with rolling trains became possible. Radios linked the caboose with the locomotive cab. Early police radio systems were initially one way using MF frequencies above the AM broadcast band, (1.7 MHz). Some early systems talked back to dispatch on a 30-50 MHz link, (called crossband).
Early mobile radios used amplitude modulation (AM)
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
to convey intelligence through the communications channel. In time, problems with sources of electrical noise showed that frequency modulation (FM)
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
was superior for its ability to cope with vehicle ignition and power line noise. The frequency range used by most early radio systems, 25 to 50 MHz (vhf "low band") is particularly susceptible to the problem of electrical noise. This plus the need for more channels led to the eventual expansion of two-way radio communications into the VHF "high band" (150 to 174 MHz) and UHF (450 to 470 MHz). The UHF band has since been expanded again.
One of the major challenges in early mobile radio technology was that of converting the six or twelve volt power supply of the vehicle to the high voltage needed to operate the vacuum tubes in the radio. Early tube-type radios used dynamotors - essentially a six or twelve volt motor that turned a generator to provide the high voltages required by the vacuum tubes. Some early mobile radios were the size of a suitcase or had separate boxes for the transmitter and receiver. As time went on, power supply technology evolved to use first electromechanical vibrators, then solid-state power supplies to provide high voltage for the vacuum tubes. These circuits, called "inverter
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
s", changed the 6V or 12V direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
(DC) to alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(AC) which could be passed through a transformer to make high voltage. The power supply then rectified this high voltage to make the high voltage DC required for the vacuum tubes, (called valves in British English). The power supplies needed to power vacuum tube radios resulted in a common trait of tube-type mobile radios: their heavy weight due to the iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-core transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s in the power supplies. These high voltage power supplies were inefficient, and the filaments of the vacuum tubes added to current demands, taxing vehicle electrical systems. Sometimes, a generator or alternator upgrade was needed to support the current required for a tube-type mobile radio.
Examples of US 1950s-1960s tube-type mobile radios with no transistors:
- Motorola FMTRU-140D (dynamotor powered)
- Motorola Twin-V, named for its "universal" 6 or 12 Volt power supply
- General Electric Progress Line (Early models without "T-Power" power supply)
- Kaar Engineering Model 501
Equipment from different US manufacturers had similar traits. This was partly dictated by Federal Communications Commission (FCC)
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
regulations. The requirement that unauthorized persons be prohibited from using the radio transmitter meant that many radios were wired so they could not transmit unless the vehicle ignition was on. Persons without a key to the vehicle could not transmit. Equipment had to be "type accepted", or technically approved, by the FCC before it could be offered for sale. In order to be type accepted, the radio set had to be equipped with an indicator light, usually green or yellow, that showed power was applied and the radio was ready to transmit. Radios were also required to have a lamp (usually red) indicating when the transmitter was on. These traits continue in the design of modern radios.
Early tube-type radios operated on 50 kHz channel spacing with plus-or-minus fifteen kilohertz modulation deviation. This meant that the number of radio channels that could be accommodated in the available radio frequency spectrum were limited to a certain number, dictated by the bandwidth of the signal on each channel.
CTCSS
In telecommunications, Continuous Tone-Coded Squelch System or CTCSS is a circuit that is used to reduce the annoyance of listening to other users on a shared two-way radio communications channel. It is sometimes called tone squelch...
tone encoders and more than two channels were unusual. Manufacturers of mobile radios built customized equipment for large radio fleets such as the California Department of Forestry and the California Highway Patrol
California Highway Patrol
The California Highway Patrol is a law enforcement agency of the U.S. state of California. The CHP has patrol jurisdiction over all California highways and also acts as the state police....
.
Examples of US hybrid partially solid state mobile radios:
- Motorola Motrac
- Motorola MJ IMTS Car Telephone (1963)
- General Electric Transistorized Progress Line
- General Electric MASTR Professional and MASTR Executive
- RCA Super Carfone
Today
Custom design for a particular customer is a thing of the past. Modern mobile radio equipment is "feature rich". A mobile radio may have 100 or more channels, be microprocessor controlled and have built-in options such as unit IDSelective 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 radio frequency channel...
. A computer and software is typically required to program the features and channels of the mobile radio. Menus of options may be several levels deep and offer a complicated array of possibilities. Some mobile radios have alphanumeric displays that translate channel numbers (F1, F2) to a phrase more meaningful to the user, such as "Providence Base", "Boston Base", etc. Radios are now designed with a myriad of features to preclude the need for custom design.
Examples of US microprocessor-controlled mobile radios:
- Motorola Astro Digital Spectra W9
- Kenwood TK-690
As use of mobile radio equipment has virtually exploded, channel spacing has had to be narrowed again to 12.5-15 kHz with modulation deviation dropping to plus-or-minus 2.5 kilohertz. In order to fit into smaller, more economical vehicles, today's radios are trending toward radically smaller sizes than their tube-type ancestors.
Details
Commercial and professional mobile radios are often purchased from an equipment supplier or dealer whose staff will install the equipment into the user's vehicles. Large fleet users may buy radios directly from an equipment manufacturer and may even employ their own technical staff for installation and maintenance.A modern mobile radio consists of a radio transceiver, housed in a single box, and a microphone with a push-to-talk button. Each installation would also have a vehicle-mounted antenna connected to the transceiver by a coaxial cable. Some models may have an external, separate speaker which can be positioned and oriented facing the driver to overcome ambient road noise present when driving. The installer would have to locate this equipment in a way that does not interfere with the vehicle's sun roof, electronic engine management system, vehicle stability computer, or air bags.
Mobile radios installed on motorcycles are subject to extreme vibration and weather. Professional equipment designed for use on motorcycles is weather and vibration resistant. Shock mounting systems are used to reduce the radio's exposure to vibration imparted by the motorcycle's modal, or resonant, shaking.
Some mobile radios use noise-canceling microphones or headsets. At speeds over 100 MPH, the ambient road and wind noise can make radio communications difficult to understand. For example, California Highway Patrol
California Highway Patrol
The California Highway Patrol is a law enforcement agency of the U.S. state of California. The CHP has patrol jurisdiction over all California highways and also acts as the state police....
mobile radios have noise-canceling microphones which reduce road and siren
Siren (noisemaker)
A siren is a loud noise making device. Most modern ones are civil defense or air raid sirens, tornado sirens, or the sirens on emergency service vehicles such as ambulances, police cars and fire trucks. There are two general types: pneumatic and electronic....
noise heard by the dispatcher
Dispatcher
Dispatchers are communications personnel responsible for receiving and transmitting pure and reliable messages, tracking vehicles and equipment, and recording other important information...
. Most fire engines and radios in heavy equipment use noise-canceling headsets. These protect the occupant's hearing and reduce background noise in the transmitted audio. Noise-canceling microphones require the operator speak directly into the front of the microphone. Hole arrays in the back of the microphone pick up ambient noise. This is applied, out-of-phase, to the back of the microphone, effectively reducing or canceling any sound which is present both in front and back of the microphone. Ideally, only the voice present on the front side of the microphone goes out on the air.
Many radios are equipped with transmitter time-out timers which limit the length of a transmission. A bane of push-to-talk systems is the stuck microphone: a radio locked on transmit which disrupts communications on a two-way radio system. One example of this problem occurred in a car with a concealed two-way radio installation where the microphone and coiled cord were hidden inside the glove box. An operator tossed the mike into the glove box and shut it, causing the push-to-talk button to be depressed and locking the transmitter on. On taxi systems, a driver may be upset when a dispatcher assigns a call (s)he wanted to another driver and may deliberately hold the transmit button down (for which the owner can be fined by the FCC). Radios with time-out timers transmit for the preset amount of time, usually 30- or 60-seconds, after which the transmitter automatically turns off and a loud tone comes out of the radio speaker. The volume level of the tone on some radios is loud and cannot be adjusted. As soon as the push-to-talk button is released, the tone stops and the timer resets.
Mobile radio equipment is manufactured to specifications developed by the Electronics Industries Association/Telecommunications Industries Association (EIA/TIA). These specifications have been developed to help ensure that mobile radio equipment not only performs as expected by the user, but also to prevent the sale and distribution of inferior equipment which could degrade communications. All specifications should be reviewed by radio system engineers to ensure that appropriate equipment is used to meet the end user's needs.
Antenna
A mobile radio must have an associated antenna. The most common antennas are stainless steel wire or rod whips which protrude vertically from the vehicle. Physics defines the antenna length: length relates to frequency and cannot be arbitrarily lengthened or shortened (more likely) by the end user. The standard "quarter wave" antenna in the 25-50 MHz range can be over nine feet long. A 900 MHz antenna may be three inches long for a quarter wavelength. A transit bus may have a ruggedized antenna, which looks like a white plastic blade or fin, on its roof. Some vehicles with concealed radio installations have antennas designed to look like the original AM/FM antenna, a rearview mirror, or may be installed inside windows, or hidden on the floor pan or underside of a vehicle. Aircraft antennas look like blades or fins, the size and shape being determined by frequencies used. Microwave antennas may look like flat panels on the aircraft's skin. Temporary installations may have antennas which clip on to vehicle parts or are attached to steel body parts by a strong magnet.Though initially relatively inexpensive mobile radio system components, frequently damaged antennas can be costly to replace since they are usually not included in maintenance contracts for mobile radio fleets. Some types of vehicles in 24-hour use, with stiff suspensions, tall heights, or rough diesel engine idle vibrations may damage antennas quickly. The location and type of antenna can affect system performance drastically. Large fleets usually test a few vehicles before making a commitment to a certain antenna location or type.
US Occupational Safety and Health Administration
Occupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...
guidelines for non-ionizing radio energy generally say the radio antenna must be two feet from any vehicle occupants. (Read the OSHA guidelines before attempting to install an antenna.) This rule of thumb is intended to result in passengers being exposed to safe levels of radio frequency energy in the event the radio transmits.
Multiple radio sets
Dispatch-reliant services, such as tow carsTow truck
A tow truck is a vehicle used to transport motor vehicles to another location , or to recover vehicles which are no longer on a drivable surface.Towing services are generally provided by an emergency road service operator...
or ambulances
Ambulance
An ambulance is a vehicle for transportation of sick or injured people to, from or between places of treatment for an illness or injury, and in some instances will also provide out of hospital medical care to the patient...
, may have several radios in each vehicle. For example, tow cars may have one radio for towing company communications and a second for emergency road service communications. Ambulances may have a similar arrangement with one radio for government emergency medical services
Emergency medical services
Emergency medical services are a type of emergency service dedicated to providing out-of-hospital acute medical care and/or transport to definitive care, to patients with illnesses and injuries which the patient, or the medical practitioner, believes constitutes a medical emergency...
dispatch and one for company dispatch.
Multiple controls, microphones
Data radio
Both tow cars and ambulances may have an additional radio which transmits and receives to support a mobile data terminalMobile data terminal
A mobile data terminal is a computerized device used in public transit vehicles, taxicabs, courier vehicles, service trucks, commercial trucking fleets, military logistics, fishing fleets, warehouse inventory control, and emergency vehicles to communicate with a central dispatch office...
. A data terminal radio allows data communications to take place over the separate radio. In the same way that a facsimile machine has a separate phone line, this means data and voice communication can take place simultaneously over a separate radio. Early Federal Express (FedEx)
FedEx
FedEx Corporation , originally known as FDX Corporation, is a logistics services company, based in the United States with headquarters in Memphis, Tennessee...
radio systems used a single radio for data and voice. The radio had a request-to-speak button which, when acknowledged, allowed voice communication to the dispatch center.
Each radio works over a single band of frequencies. If a tow car company had a frequency on the same band as its auto club, a single radio with scanning might be employed for both systems. Since a mobile radio typically works on a single frequency band, multiple radios may be required in cases where communications take place over systems on more than one frequency band.