Thursday, January 12, 2012

Pager portable, lightweight receiver of coded radio signals


Pager
Pager
Pagers notify their owners that someone is trying to contact them, usually by beeping or vibrating. The liquid crystal display can display short messages or telephone numbers.

Pager, portable, lightweight receiver of coded radio signals that indicates to its user that a message is waiting or someone is trying to get in touch. When people want to page someone—that is, contact a person via the person’s pager—they telephone a paging service company, which then sends wireless radio signals to the pager. These signals, in turn, alert the pager’s user by triggering a tone or a vibration. Most pagers can also deliver brief messages on liquid crystal displays. Because pagers do not rely on telephone wires, a page can be transmitted from a central location and received anywhere within the range of the transmitting tower (see Wireless Communications). Pagers make their users easy to contact, even if the user is away from a telephone. As a result, pagers help increase productivity and improve responsiveness to emergencies and to business and personal requests.
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HOW A PAGER WORKS
A page is the coded radio signal sent from a transmitter to the pager. Pages usually begin with the dialing of a telephone number to the user’s paging service provider, a company that maintains the paging transmitters and radio equipment. Placing a telephone call to the service provider enables the caller to access a computerized terminal. The caller hears a tone or receives instructions on how to page a subscriber. If the caller wants to leave a telephone number for the paged party to call, the caller can enter that number. Pressing the telephone’s pound (#) or star (*) key informs the paging terminal that the message is complete.
The paging terminal automatically determines which pager corresponds to the telephone number dialed. It then routes a signal to one or more radio transmitters located throughout the paging service area. The area can vary; some services are local, while others are networked together via satellite to cover larger regions.
Pagers monitor specific radio frequencies used by the service providers. The transmission of the page is encoded so that only the intended recipient of the page can receive and decode the message. If the pager is switched on and is within range of the radio tower, the pager will recognize the coded signal. The pager then converts the signal to data, alerting the owner that a page has been sent with a beep, tone, or vibration. Most pagers have liquid-crystal displays that can show the number of the calling party, or short messages. The owner of the pager can telephone the paging party, or call the paging company to retrieve other messages.
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HISTORY
The use of radio signals to perform one-way notifications began in the 1920s and 1930s. During the same period, mobile radio systems were being developed for police dispatch and public safety services. These early systems broadcast messages to all receivers on the band, and they could not be used to contact a specific party.
Paging later developed from a one-to-many dispatch service into a system for reaching a single address that corresponded to one pager. Pagers in the 1960s and 1970s were simple devices that used a tone or vibration to alert the subscriber to call a single predetermined number to get the message. Communications satellites are commonly used to route pager connections throughout the United States, and in 1998 a satellite failure temporarily silenced millions of pagers across the United States. Pager connections were transferred to another satellite to restore service.
Innovations in computer technology have improved pagers, making them smaller, more affordable, and loaded with new features. Modern pagers have screens that can display numbers or short messages, and they can store those messages for future referral. Pager users can subscribe to special services that broadcast information such as stock market quotations and up-to-the minute sports scores. The next generation of pagers will include the ability to acknowledge reception of a page and respond with a short, predetermined message.

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