walkie-talkie

A walkie-talkie (more formally known as a handheld transceiver) is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald L. Hings, radio engineer Alfred J. Gross, and engineering teams at Motorola. Similar designs were created for other armed forces, and after the war, walkie-talkies spread to public safety and eventually commercial and jobsite work. Major characteristics include a half-duplex channel (only one radio transmits at a time, though any number can listen) and a "push-to-talk" (PTT) 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 the user's immediate vicinity. Hand-held transceivers may be used to communicate between each other, or to vehicle-mounted or base stations.

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Military

Military organizations use handheld radios for a variety of purposes. Modern units such as the AN/PRC-148 Multiband Inter/Intra Team Radio (MBITR) can communicate on a variety of bands and modulation schemes and include encryption capabilities.

Amateur radio

Walkie-talkies (also known as HTs or "handheld transceivers" ) are widely used among amateur radio operators. While converted commercial gear by companies such as Motorola are not uncommon, many companies such as Yaesu, Icom, and Kenwood design models specifically for amateur use. While superficially similar to commercial and personal units (including such things as CTCSS and DCS squelch functions, used primarily to activate amateur radio repeaters), amateur gear usually has a number of features that are not common to other gear, including:

• Wide-band receivers, often including radio scanner functionality, for listening to non-amateur radio bands.
• Multiple bands; while some operate only on specific bands such as 2 meters or 70 cm, others support several UHF and VHF amateur allocations available to the user.
• Since amateur allocations usually are not channelized, the user can dial in any frequency desired in the authorized band.
• Multiple modulation schemes: a few amateur HTs may allow modulation modes other than FM, including AM, SSB, and CW,and digital modes such as radioteletype or PSK31. Some may have TNCs built in to support packet radio data transmission without additional hardware.

A newer addition to the Amateur Radio service is Digital Smart Technology for Amateur Radio or D-STAR. Handheld radios with this technology have several advanced features, including narrower bandwidth, simultaneous voice and messaging, GPS position reporting, and callsign routed radio calls over a wide ranging international network.
As mentioned, commercial walkie-talkies can sometimes be reprogrammed to operate on amateur frequencies. Amateur radio operators may do this for cost reasons or due to a perception that commercial gear is more solidly constructed or better designed than purpose-built amateur gear.

Personal use

The personal walkie-talkie has become popular also because of the U.S. Family Radio Service (FRS) and similar unlicensed services (such as Europe's PMR446 and Australia's UHF CB) in other countries. While FRS walkie-talkies are also sometimes used as toys because mass-production makes them low cost, they have proper superheterodyne receivers and are a useful communication tool for both business and personal use. The boom in unlicensed transceivers has, however, been a source of frustration to users of licensed services that are sometimes interfered with. For example, FRS and GMRS overlap in the United States, resulting in substantial pirate use of the GMRS frequencies. Use of the GMRS frequencies (USA) requires a license; however most users either disregard this requirement or are unaware. Canada reallocated frequencies for unlicensed use due to heavy interference from US GMRS users. The European PMR446 channels fall in the middle of a United States UHF amateur allocation, and the US FRS channels interfere with public safety communications in the United Kingdom. Designs for personal walkie-talkies are in any case tightly regulated, generally requiring non-removable antennas (with a few exceptions such as CB radio and the United States MURS allocation) and forbidding modified radios.

A Motorola FRS radio with labeled parts

Most personal walkie-talkies sold are designed to operate in UHF allocations, and are designed to be very compact, with buttons for changing channels and other settings on the face of the radio and a short, fixed antenna. Most such units are made of heavy, often brightly colored plastic, though some more expensive units have ruggedized metal or plastic cases. Commercial-grade radios are often designed to be used on allocations such as GMRS or MURS (the latter of which has had very little readily available purpose-built equipment). In addition, CB walkie-talkies are available, but less popular due to the propagation characteristics of the 27 MHz band and the general bulkiness of the gear involved.
Personal walkie-talkies are generally designed to give easy access to all available channels (and, if supplied, squelch codes) within the device's specified allocation.
Personal two-way radios are also sometimes combined with other electronic devices; Garmin's Rino series combine a GPS receiver in the same package as an FRS/GMRS walkie-talkie (allowing Rino users to transmit digital location data to each other) Some personal radios also include receivers for AM and FM broadcast radio and, where applicable, NOAA Weather Radio and similar systems broadcasting on the same frequencies. Some designs also allow the sending of text messages and pictures between similarly equipped units.
While jobsite and government radios are often rated in power output, consumer radios are frequently and controversially rated in mile or kilometer ratings. Because of the line of sight propagation of UHF signals, experienced users consider such ratings to be wildly exaggerated, and some manufacturers have begun printing range ratings on the package based on terrain as opposed to simple power output.
While the bulk of personal walkie-talkie traffic is in the 27 MHz area and in the 400-500 MHz area of the UHF spectrum, there are some units that use the 49 MHz band (shared with cordless phones, baby monitors, and similar devices) as well as the 900 MHz band; in the US at least, units in these bands do not require licenses as long as they adhere to FCC power output rules. A company called TriSquare is, as of July 2007, marketing a series of walkie-talkies in the United States based on frequency-hopping spread spectrum technology operating in this frequency range under the name eXRS (eXtreme Radio Service—despite the name, a proprietary design, not an official allocation of the US FCC). The spread-spectrum scheme used in eXRS radios allows up to 10 billion virtual "channels" and ensures private communications between two or more units.

Recreation

Low-power versions, exempt from licence requirements, are also popular children's toys such as the Fischer Price Walkie-Talkie for children illustrated in the top image on the right. Prior to the change of CB radio from licensed to "permitted by part" (FCC rules Part 95) status, the typical toy walkie-talkie available in North America was limited to 100 milliwatts of power on transmit and using one or two crystal-controlled channels in the 27 MHz citizens' band using amplitude modulation (AM) only. Later toy walkie-talkies operated in the 49 MHz band, some with frequency modulation (FM), shared with cordless phones and baby monitors. The lowest cost devices are very simple electronically (single-frequency, crystal-controlled, generally based on a simple discrete transistor circuit where "grownup" walkie-talkies use chips), may employ superregenerative receivers, and may lack even a volume control, but they may nevertheless be elaborately decorated, often superficially resembling more "grown-up" radios such as FRS or public safety gear. Unlike more costly units, low-cost toy walkie-talkies may not have separate microphones and speakers; the receiver's speaker sometimes doubles as a microphone while in transmit mode.

An inexpensive children's walkie-talkie.

An unusual feature, common on children's walkie-talkies but seldom available otherwise even on amateur models, is a "code key", that is, a button allowing the operator to transmit Morse code or similar tones to another walkie-talkie operating on the same frequency. Generally the operator depresses the PTT button and taps out a message using a Morse Code crib sheet attached as a sticker to the radio; however, as Morse Code has fallen out of wide use outside amateur radio circles, some such units either have a grossly simplified code label or no longer provide a sticker at all.
In addition, personal UHF radios will sometimes be bought and used as toys, though they are not generally explicitly marketed as such (but see Hasbro's ChatNow line, which transmits both voice and digital data on the FRS band).

Specialized uses

In addition to land mobile use, walkie-talkie designs are also used for marine VHF and aviation communications, especially on smaller boats and aircraft where mounting a fixed radio might be impractical or expensive. Often such units will have switches to provide quick access to emergency and information channels.
Intrinsically safe walkie-talkies are often required in heavy industrial settings where the radio may be used around flammable vapors. This designation means that the knobs and switches in the radio are engineered to avoid producing sparks as they are operated.