Walkie-talkie
A walkie-talkie, more formally known as a handheld transceiver (HT), is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald Hings, radio engineer Alfred J. Gross, Henryk Magnuski and engineering teams at Motorola. First used for infantry, similar designs were created for field artillery and tank units, and after the war, walkie-talkies spread to public safety and eventually commercial and jobsite work. Typical walkie-talkies resemble a telephone handset, with a speaker built into one end and a microphone in the other (in some devices the speaker also is used as the microphone) and an antenna mounted on the top of the unit. They are held up to the face to talk. A walkie-talkie is a half-duplex communication device. Multiple walkie-talkies use a single radio channel, and only one radio on the channel can transmit at a time, although any number can listen. The transceiver is normally in receive mode; when the user wants to talk they must press a "push-to-talk" (PTT) button that turns off the receiver and turns on the transmitter. Some cellular telephone networks offer a push-to-talk handset that allows walkie-talkie-like operation over the cellular network, without dialling a call each time. However, the cellphone provider must be accessible. Some units have additional features such as sending calls, call reception with vibration alarm, keypad locking, and a stopwatch. Smaller walkie-talkie are also very popular among young children. In line to the ITU Radio Regulations, article 1.73, a walkie-talkie is classified as radio station/land mobile station. Handheld two-way radios were developed by the military from backpack radios carried by a soldier in an infantry squad to keep the squad in contact with their commanders. Probably the first patent owner (patent filled on 20 May 1935, granted on 19 March 1936) was the engineer Henryk Magnuski from Poland, who later worked since 1939 on Motorola's first walkie-talkie (a hand-held radio transceiver SCR-536).