Mobile radio
Mobile radios are mounted to a motor vehicle usually with the microphone and control panel in reach of the driver.
[citation needed] The backbone or infrastructure supporting the system defines which category or taxonomy applies.
[citation needed] Two-way radio is primarily a dispatch[citation needed] 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.
Railroads used medium frequency range (MF) communications (similar to the AM broadcast band) to improve safety.
Early police radio systems were initially one way using MF frequencies above the AM broadcast band, (1.7 MHz).
Early mobile radios used amplitude modulation (AM) to convey intelligence through the communications channel.
The frequency range used by most early radio systems, 25–50 MHz (vhf "low band") is particularly susceptible to the problem of electrical noise.
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.
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: Equipment from different US manufacturers had similar traits.
A mobile radio may have 100 or more channels, be microprocessor controlled and have built-in options such as unit ID.
A computer and software is typically required to program the features and channels of the mobile radio.
For example, Hytera's HM68X mobile radio, which was introduced in September 2022, offers a variety of features, including GPS location, emergency alarm, noise cancellation, and more.
The traditional analogue radio communications have been surpassed by digital radio voice communications capabilities that provide greater clarity of transmission, enable security features such as encryption and, within the network, allow low band data transmissions to accommodate simple text or picture messaging as an example.
Large fleet users may buy radios directly from an equipment manufacturer and may even employ their own technical staff for installation and maintenance.
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.
Shock mounting systems are used to reduce the radio's exposure to vibration imparted by the motorcycle's modal, or resonant, shaking.
At speeds over 100 MPH, the ambient road and wind noise can make radio communications difficult to understand.
For example, California Highway Patrol mobile radios have noise-canceling microphones which reduce road and siren noise heard by the dispatcher.
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.
The most common antennas are stainless steel wire or rod whips which protrude vertically from the vehicle.
Some types of vehicles in 24-hour use, with stiff suspensions, tall heights, or rough diesel engine idle vibrations may damage antennas quickly.
[7] Both tow cars and ambulances may have an additional radio which transmits and receives to support a mobile data terminal.
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.
