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Land mobile radio systems use channels in the VHF or UHF bands, since the antennas used at these short wavelengths are small enough to mount on vehicles or handheld transceivers. Transmitter power is usually limited to a few watts, to provide a reliable working range on the order of 3 to 20 miles (4.8 to 32 km) depending on terrain.
The frequency range used by most early radio systems, 25–50 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" (150–174 MHz) and UHF (450–470 MHz).
In commercial systems, cross-band repeaters are sometimes used in vehicular repeaters. For example, a 150 MHz hand held may communicate to a vehicle-mounted low-power transceiver. The low-power radio repeats transmissions from the portable over the vehicle's high power mobile radio, which has a much longer range.
Small monopoles ("whips") are used as compact, but low-gain antennas on portable radios in the HF, VHF, and UHF bands. Whip Type of antenna used on mobile and portable radios in the VHF and UHF bands such as FM "boom boxes", consists of a flexible rod, often made of telescoping segments
Theoretically, the range between two hand-held units on flat ground would be about one or two miles (about 1.5–3 km). Mobile units might have a slightly farther range when mounted on a car roof. A GMRS repeater with an antenna mounted high above the surrounding terrain can extend the usable range to 20 miles or more (30+ km) depending on height.
Naval air traffic controller communicates with aircraft over a two-way radio headset A variety of portable handheld two-way radios for private use. A two-way radio is a radio transceiver (a radio that can both transmit and receive radio waves), which is used for bidirectional person-to-person voice communication with other users with similar radios, [1] in contrast to a broadcast receiver ...
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 and portable two-way radios communicate over a single shared radio channel, with one user at a time ...
An amateur radio repeater system consisting of a 70 cm repeater and a 2-meter digipeater and iGate. Coaxial cavity RF filter at 2 meter repeater An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer ...
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