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Pagers are inexpensive radio receivers that notify the user of the existence of a message. The simplest versions simply provide an indication as the presence of a message (beep, light, etc); the user must then call a mailbox to get the message contents. More sophisticated pagers can actually convey simple messages, ranging from a telephone number to call to an alpha-numeric display several lines long. Receive only pagers do not have any response capability, only receive capability.
The typical system functions by having a high-powered transmitter send signals to the subscribers. This allows the use of relatively inexpensive receivers having only moderate sensitivity. It also means that a pager is most commonly only useful in a local geography, such a major metropolitan area.
Traditional paging bands have been at 50 MHz, 200 MHz, and more recently at 900MHz. Emphasis is on low cost, low current consumption for long battery life, and 1 V operation.
A typical solution will use inexpensive discrete transistors as LNA, mixer, gain stage, and oscillator. Cascode front ends are popular as they give excellent stability and insensitivity to input antenna configuration, important considerations for portable, miniature receivers that may be placed in a variety of environments. In major metropolitan areas, pagers may incorporate a front end PIN diode attenuator to reduce receiver sensitivity, thus eliminating distortion due to saturation.
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