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A walkie-talkie is a portable, bi-directional radio transceiver, first developed for military use. Major characteristics include a half-duplex (only one of receive or transmit at a time) channel and a push-to-talk switch that starts transmission. The typical physical format looks like a telephone handset, possibly slightly larger but still a single unit, with an antenna sticking out of the top.
Prior to the change of CB radio from licensed to un-licensed status, the typical walkie-talkie available in retail stores in North America was limited to 100 milliwatts of power on transmit and the 27 MHz CB channels. Other walkie-talkies were licensed for police and commercial bands, typically in the 49 MHz range, where the first cordless phones were also assigned.
The first radio receiver/transmitter to be nick-named walkie-talkie was the Motorola SCR-300 invented by Henryk Magnuski in 1940. Motorola also produced the SCR-536 radio during the war, and it was called the "Handie-Talkie".
The personal walktie-talkie has now become popular again with the Family Radio Service. FRS operates in the GMRS band, which is itself used for business walkie-talkies.