- A "two-way" radio is a wireless communication device that receives and transmits radio waves on a single frequency. The device is configured to receive until a switch is activated that allows the operator to transmit. Two-way radios may be stationary (a "base" unit) or they may be portable, "hand-held" units powered by batteries. The size of the battery and range of the receiver determine the size of the hand-held unit.
- The earliest radio transmissions allowed no feedback. Two-way communication was possible only by using a transmitter set up near a receiver. An Australian police constable was the first to combine the two functions into one large unit that sat in the back seat of his police car. By the 1930's, radios had increased in range and reliability and could communicate with a base unit. Two-way technology was advanced by the military use of the radios in World War II, resulting in smaller units that could receive and transmit on a number of frequencies. Postwar developments built on the military model, using a base station and portable units to establish a network of radios. As the popularity of the hand-held radios grew, the single channel (simplex) limitation on transmission was solved by using two frequencies (duplex) to make a channel over which speakers could transmit and receive at the same time.
- Two-way radios operate on one or more radio frequencies (RF) and can be tuned to a specific channel rather than operating within a range as larger transmitters do. Their range is limited, allowing one user to operate on one channel without interference from a user in a neighboring area. Most governments, whose public safety departments use two-way radios extensively, assign specific channels to each department so that emergency communications can flow without confusion. Not all radios are made with the same channel choices, though---these are programmed in by the manufacturer. Communication problems such as arose on 9-11 in New York occur when different departments cannot communicate because their radios have been programmed with different sets of RF channels.
- Two-way radios are available in a number of styles and formats. "Walkie-Talkie" radios are small hand-held, battery-powered simplex sets, used for easy communication within a distinct area. Emergency services usually choose the larger duplex or multiplex (multiple channels) hand held sets that are larger and generally are re-charged between shifts in the base unit. Permanent units installed in emergency vehicles. "Base" units are situated at a corporate headquarters or on the dispatch desk. Modern radios are available using analog or digital signals and can have unique capabilities from paging to Internet access.
- Amateur radio buffs build their own two-way radios and have contributed by aiding emergency personnel and bringing news to people isolated by disasters. Two-way radios are convenient and fun as a hobby but their greatest value is in an emergency when dialing a number (even if it's on speed dial) takes time and a group of people requires simultaneous notification.
