two way – a term than carries so much meaning for radio communication. So what does “two way” mean?
two way radio – A two way radio is a radio that can both transmit and receive (a transceiver), unlike a broadcast receiver which only receives content.
Two way radios are available in mobile, stationary base and hand-held portable configurations. Hand-held radios are often called walkie-talkies or handie-talkies. A push-to-talk or Press To Transmit button is often present to activate the transmitter.
A mobile phone or cellular telephone is an example of a two way radio that both transmits and receives at the same time (or full-duplex). It uses two different radio frequencies to carry the two directions of the conversation simultaneously.
Installation of receivers and transmitters at the same fixed location allowed exchange of messages wirelessly. As early as 1907, two way telegraphy traffic across the Atlantic Ocean was commercially available. By 1912 commercial and military ships carried both transmitters and receivers, allowing two way communication in close to real-time with a ship that was out of sight of land.
The first truly mobile two way radio was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police. The Victoria Police were the first in the world to use wireless communication in cars, putting an end to the inefficient status reports via public telephone boxes which had been used until that time. The first sets took up the entire back seat of the Lancia patrol cars.
As radio equipment became more powerful, compact, and easier to use, smaller vehicles had two-way radio communication equipment installed. Installation of radio equipment in aircraft allowed scouts to report back observations in real-time, not requiring the pilot to drop messages to troops on the ground below or to land and make a personal report.
In 1933, the Bayonne, New Jersey police department successfully operated a two way system between a central fixed station and radio transceivers installed in police cars; this allowed rapidly directing police response in emergencies. During World War II hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Nazis.
Early two way schemes allowed only one station to transmit at a time while others listened, since all signals were on the same radio frequency – this was called “simplex” mode. Code and voice operations required a simple communication protocol to allow all stations to cooperate in using the single radio channel, so that one station’s transmissions were not obscured by another’s. By using receivers and transmitters tuned to different frequencies, and solving the problems introduced by operation of a receiver immediately next to a transmitter, simultaneous transmission and reception was possible at each end of a radio link, in so-called “full duplex” mode.