ANDYCOM

A two-way radio is a radio that can do both transmit and receive a signal, unlike a broadcast receiver which only receives content.
A two-way radio (transceiver) allows the operator to have a conversation with other similar radios operating on the same radio frequency.
Two-way radios are available in mobile, stationary base and hand-held portable configurations.
Two-way radio systems usually operate in a half-duplex mode; This means the operator can talk, or he can listen, but not at the same time.
A push-to-talk or Press to Transmit button activates the transmitter; when it is released the receiver is active.
Full-duplex is generally achieved by the use of two different frequencies or by frequency-sharing methods to carry the two directions of the conversation simultaneously.
The useful direct range of a two-way radio system depends on radio propagation conditions, which are a function of frequency, antenna height and characteristics,
atmospheric noise, reflection and refraction within the atmosphere, transmitter power and receiver sensitivity, and required signal-to-noise ratio for the chosen modulation method.
Two-way systems operating in the VHF and UHF bands, where many land mobile systems operate, rely on line-of-sight propagation for the reliable coverage area.
The "shadowing" effect of tall buildings may block reception in areas within the line-of-sight range which can be achieved in open countryside free of obstructions.
There are other factors that affect the range of a two-way radio such as weather, exact frequency used, and obstructions.