Walkie-talkie
From Wikipedia, the free encyclopedia
A walkie-talkie (more formally known as a handheld transceiver) is a hand-held, portable, two-way radio transceiver. Originally developed for the Canadian government during the Second World War by Canadian Donald L. Hings, similar designs were created for other armed forces, and after the war, walkie-talkies spread to public safety and eventually commercial and jobsite work after the war. Major characteristics include a half-duplex channel (only one radio transmits at a time, though any number can listen) and a push-to-talk switch that starts transmission. Typical walkie-talkies resemble a telephone handset, possibly slightly larger but still a single unit, with an antenna sticking out of the top. Where a phone's earpiece is only loud enough to be heard by the user, a walkie-talkie's built-in speaker can be heard by the user and those in his immediate vicinity. Hand-held transceivers may be used to communicate between each other, or to vehicle-mounted or base stations.
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[edit] History
The first radio receiver/transmitter to be nick-named "Walkie-Talkie" was the backpacked Motorola SCR-300, created by an engineering team in 1940 at the Galvin Manufacturing Company (fore-runner of Motorola). The team consisted of Dan Noble, who conceived of the design using frequency modulation, Henryk Magnuski who was the principal RF engineer, Marion Bond, Lloyd Morris, and Bill Vogel.
Motorola also produced the hand-held AM SCR-536 radio during World War II, and it was called the "Handie-Talkie" (HT). The terms are often confused today, but the original walkie talkie referred to the back mounted model, while the handie talkie was the device which could be held entirely in the hand (but had vastly reduced performance). Both devices ran on vacuum tubes and used high voltage dry cell batteries. (Handie-Talkie became a trademark of Motorola, Inc. on May 22, 1951. The application was filed with the U.S. Patent and Trademark Office,and the trademark registration number is 71560123. )
The abbreviation HT, derived from Motorola's "Handie Talkie" trademark, is commonly used to refer to portable handheld ham radios, with "walkie-talkie" often used as a layman's term or specifically to refer to a toy. Public safety or commercial users generally refer to their handhelds simply as "radios". Surplus Motorola Handie Talkies found their way into the hands of ham radio operators immediately following World War II. Motorola's public safety radios of the 1950s and 1960s, were loaned or donated to ham groups as part of the Civil Defense program. To avoid trademark infringement, other manufacturers use designations such as "Handheld Transceiver" or "Handie Transceiver" for their products.
Al Gross also worked on the early technology behind the walkie-talkie between 1934 and 1941, and is sometimes said to actually have invented it.
Donald Hings was formally decorated for the invention of the walkie-talkie and its significance to the war effort.[1] Hing's model C-58 "Handy-Talkie" was in military service by 1942, following a secret R&D effort that began in 1940. The C-58 was in turn based on a civilian model originally developed by him in 1937.
Following World War II, Raytheon developed the SCR-536's military replacement, the AN/PRC-6. The AN/PRC-6 circuit uses 13 tubes (receiver and transmitter); a second set of 13 tubes is supplied with the unit as running spares. The unit is factory set with one crystal and may be changed to a different frequency in the field by replacing the crystal and re-tuning the unit. It uses a 24 inch whip antenna. There is an optional handset H-33C/PT that can be connected to the AN/PRC-6 by a 5 foot cable. A web sling is provided.
In the mid-1970s the Marine Corps initiated an effort to develop a squad radio to replace the unsatisfactory helmet-mounted AN/PRR-9 receiver and receiver/transmitter hand-held AN/PRT-4 (both developed by the Army). The AN/PRC-68 was first produced in 1976 by Magnavox, was issued to the Marines in the 1980s, and was adopted by the US Army as well.
[edit] Developments
Since even a powerful commercial walkie-talkie is limited to a few watts of power output and a small antenna (the physical size of the package limits both battery capacity and antenna size), hand-held communication range is typically quite short, not exceeding the line-of-sight distance to the horizon in open areas, and very much less in built-up areas, within buildings, or underground. Many radio services permit the use of a repeater which is located at some high point within the desired coverage area. The repeater listens on one frequency and retransmits on another, so that reliable hand-held to hand-held unit range can be extended to a few score miles (kilometers) or further, using repeaters linked together.
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. *
Walkie-talkies for public safety, commercial and industrial uses may be part of trunked radio systems, which dynamically allocate radio channels for more efficient use of limited radio spectrum.
