A radio communication system is a collection of fixed and mobile radio equipment designed to serve an organization by allowing specific communication modes like one-to-many and one-to-one. The common radio communication system uses one or more fixed sites, which have the ability to repeat and relay messages to nearby and remote sites as needed. The two-way radio allows people to exchange messages, whereas radio broadcasting is a transfer of information in one direction only. Many frequency bands and modulation types are used for the radio communication system. Frequencies from 0.3 megahertz (MHz) to about 3,000 MHz assigned into the so-called high frequency, very high frequency, and ultrahigh frequency for various specific needs are extra long range, all-terrain, and urban structure signal penetration.
The modern two-way radio system (2WRS), which is an alternative name for radio communication system, typically has three user modes. A portable radio user has a handheld transmitter-receiver, or transceiver, device that runs on batteries and is easy enough to take almost anywhere, a mobile radio user usually has a transceiver mounted inside a vehicle, and a fixed or base radio user sits at a station with stationary radio equipment. The transportable radio may be carried and operated during stationary times. Radio electronics has improved a lot since the early 1900s, as there have been breakthroughs in battery technology that increase the talk time for portable radios. Some technologies even allow for radio transmit power auto-adjustment to match the user locations relative to the fixed stations.
Radio communication system users are able to communicate to all members of a group at the same time. In practice, each group in an organization is granted an actual channel or a virtual private channel where the group can communicate without interfering with communications from other groups. This feature is made possible by channel selectivity of radio receivers used in conventional analog communications.
In conventional analog communications, channels are allocated to different groups, and when there are too many groups, a technique called trunking allows radio groups to have a virtual channel as needed. In this mode, the trunking radio communication system requires a form of data communication-capable subscriber units called trunked radios. Instead of using a channel exclusively, a trunked radio will automatically request a channel without the user knowing it. All the user knows is that there is access to a specific virtual channel or talk group. A go-ahead beep informs the user that a virtual channel has been established and that the user may already speak.