Cordless telephone

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 handover, various advanced features, such as data-transfer and even, on a limited scale, international roaming. In these 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 pretty 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 over several 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 sits in its cradle. A jazz musician named Teri Pall invented a version of the cordless phone in 1965 but could not market her invention as its two-mile range caused radio signals to interfere with aircraft. She sold her rights to the cordless phone in 1968 to a manufacturer who modified it for practical use.[1] George Sweigert, an amateur radio operator and inventor from Cleveland, Ohio, is largely recognized as the father of the cordless phone.[2] Google Patents link. [1] He submitted a patent application in 1966 for a "full duplex wireless communications appartus"[sic]. The U.S. Patent and Trademark Office awarded him a patent in June 1969 (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 pe

sonnel, to improve battlefield communications for senior commanders. He was also licensed as W8ZIS and N9LC in the amateur radio service. He also held a First Class Radiotelephone Operator's Permit issued by the Federal Communications Commission. 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 rented 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 1968 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). Filed 03/11/1974, Douglas G. Talley and L Duane Gregory applied for and were granted (08/02/1977) US Patent 4039760 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. In the 1980s, a number of manufacturers, including Sony, introduced cordless phones for the consumer market. Typically, they used a base station that was connected to a telephone line and a handset with a microphone, speaker, keypad, and telescoping antenna. The handset contained a rechargeable battery, typically NiCd; the base unit was powered by household current, typically via an AC adaptor. The base included a charging cradle, which was generally a form of trickle charger, on which the handset rested when not in use. Some cordless telephones now utilize two rechargeable AA or AAA cells in place of the more expensive traditional proprietary telephone batteries. Since the 1980s, several companies have entered the cordless-phone market: VTech, Uniden, Philips, Gigaset and Panasonic. They advertise many new features,[which?] a few provided by the phone and most provided by the network.