Pager
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Paging is still in use today by organisations who need to send urgent information to people quickly and cheaply.
Paging was invented in 1956 at St Thomas hospital in London to alert doctors attending emergencies. Since then, paging has evolved in sophistication and today millions of messages are transmitted to people needing fast reliable messaging communications.
In the world of paging there are two distinct categories of system in operation. There are on-site paging systems that are used in hospitals to convey the same urgent information when invented in 1956. The other is wide area paging, which offers similar features as on-site paging, but provides the radio coverage across the whole of the UK rather than in just one hospital building.
At the heart of these paging systems are three types of paging message. The first is the alert message where the pager provides an audible alert, coining the phrase, ‘beep’ or ‘beeper’. The user who receives a beep message would contact the switch board or control room to get the message. This type of message uses a tone pager.
Second, is the number message where the pager will beep and display a number message for the user to call. The number message provides more flexibility over the alert message if more than one person wants to get hold of you.
The number messages can be up to 20 digits in length and can represent information other than telephone numbers. Some popular examples would be 925 (finished work), 1426 0142 representing a NGR grid reference.
The final message type is the word message, where the pager will beep and display a word message of up to 1000 characters. In this type of message any information or action can be conveyed to the user and acts much like a text message on a mobile telephone.
Unlike any other present day radio network, the paging network sends the messaging information to all the wireless transmitters simultaneously. This means that one message can be sent to many people at the same time if they share the same pager alert number. This is referred to as a ‘paging broadcast’, and is one of the key factors why businesses and emergency organisations continue to use paging today.
Common paging protocols include Telocator Alphanumeric input Protocol (TAP), FLEX, ReFLEX, POCSAG, Golay and NTT. Past paging protocols include Two-tone and 5/6-tone.
In the United States, pagers typically receive signals using the FLEX protocol in the 900MHz band. Commercial paging transmitters typically radiate 1000 watts of effective power, resulting in a much wider coverage area per tower than a mobile phone transmitter, which typically radiates in the neighborhood of 0.6 Watt per channel.
Although 900MHz FLEX paging networks tend to have stronger in-building coverage than mobile phone networks, commercial paging service providers will work with large institutions to install repeater equipment in the event that service is not available in needed areas of the subscribing institution's buildings. This is especially critical in hospital settings where emergency staff must be able to reliably receive pages in order to respond to patient needs.
Other radio bands used for pagers include the 400MHz band, the VHF band, and the FM commercial broadcast band (88-108MHz). Other paging protocols used in the VHF, 400MHz UHF, and 900MHz bands include POCSAG and ERMES. Pagers using the commercial FM band receive a subcarrier, called the Subsidiary Communications Authority, of a broadcast station.
