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A cordless telephone or portable telephone replaces the handset cord with a radio link. The handset communicates with a base station connected to a fixed telephone line. The range is limited, usually to the same building or some short distance from the base station. The base station attaches to the telephone network the same way a corded telephone does. The base station on subscriber premises is what differentiates a cordless telephone from a mobile telephone. Current cordless telephone standards, such as PHS and DECT, have blurred the once clear-cut line between cordless and mobile telephones by implementing cell handoff (handover); various advanced features, such as data-transfer; and even, on a limited scale, international roaming. In specialized models, base stations are maintained by a commercial mobile network operator and users subscribe to the service. In 1994, digital cordless phones in the 900 MHz frequency range were introduced. Digital signals allowed the phones to be more secure and decreased eavesdropping—it was relatively easy to eavesdrop on analog cordless phone conversations. In 1995, digital spread spectrum (DSS) was introduced for cordless phones. This technology enabled the digital information to spread in pieces among multiple frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on the cordless conversations. Unlike a corded telephone, a cordless telephone needs mains electricity to power the base station. The cordless handset is powered by a rechargeable battery, which is charged when the handset is stored in its cradle. ==History== A jazz musician named Teri Pall invented a version of the cordless phone in 1965 but could not market her invention, as its range caused its radio signals to interfere with aircraft communications. In 1968, she sold her rights to the cordless phone to a manufacturer who modified it for practical use.〔(Patently female: from AZT to TV dinners : stories of women inventors and their breakthrough ideas, Ethlie Ann Vare, Greg Ptacek )〕 In 1966, George Sweigert submitted a patent application for a "full duplex wireless communications appartus". He was awarded in June 1969〔 DUPLEX RADIO COMMUNICATION AND SIGNALING APPARATUS FOR PORTABLE TELEPHONE ... G. H. SWEIGERT〕〔(Google Patents link )〕 He (see below: ''Patents''). Sweigert, a radio operator in World War II stationed at the South Pacific Islands of Guadalcanal and Bougainville, developed the full duplex concept for untrained personnel, to improve battlefield communications for senior commanders. Sweigert was an active proponent for directly coupling consumer electronics to the AT&T-owned telephone lines in the late 1960s. (This was banned at the time; most telephones were made by Western Electric and leased to the customer by AT&T.) The Carterfone coupler, a crude device for interconnecting a two-way radio with the telephone, led to the reversal of the Federal Communications Commission ban on direct coupling of consumer equipment to phone lines (known as the landmark Carterfone decision) on June 26, 1968. The original cordless phones, like the Carterfone, were acoustically (not electrically) connected to the Public Switched Telephone Network (PSTN). In 1977, Douglas G. Talley and L Duane Gregory were granted for a duplex voice communication link including controls therefore as provided between a base station connected directly to a telephone line of a telephone exchange and a mobile unit consisting of a small, compact cordless telephone instrument containing transmitter, receiver and control circuits powered by a rechargeable battery pack. A single logic tone is transmitted and detected for all logical control for ring signals, on-hook and off-hook signals and dial pulses. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cordless telephone」の詳細全文を読む スポンサード リンク
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