The History of the Two-Way Pager
An interesting device, released a little too late
In the 90s, pagers were popular: They were cheap, lightweight, and had a very long battery life. But at the same time, they were only able to receive messages. There was no transmitter inside the pager, and there was no physical possibility to send any response. The idea of having two-way communication was tempting, and in 1995 the Motorola Tango, the first pager that was able not only to receive but also to send messages, was made.
All pagers from the paging provider listen to the same frequency, let’s say, 930 MHz. Every pager has its own unique ID, called CAP — Channel Access Protocol or RIC — Receiver Identification Code. If the message code is equal to the pager code, the pager saves the message and makes the loud “beep.” That’s it. It’s one-way communication. There is no confirmation sent back. The pager has only the receiver and no transmitter at all. The logic and hardware are extremely simple, and because of that, the pager can work for more than a month from a single AAA battery.
This scheme has several advantages. Firstly, all the messages are sent one after another, on the same frequency, which means that the system can’t be overloaded. If the new message is received by the operator, it will be added to the end of the queue. Secondly, each transmitter tower covers a large area — usually, the antenna is located on the toll building, and a high-power transmitter can be used. This system can provide up to 50 km coverage on the open space or 5–10 km in the city, with relatively simple hardware. In general, this system is cheap and reliable, and because of that, pagers are still in use even now in hospitals and for emergency communication.
But what do we need if we want to send messages from the pager? Engineers created several solutions to implement this:
- The pager is using separated frequencies to get and send messages. The Motorola Talkabout pager, displayed on the photo, is using the 929–942 MHz frequency range to receive data and 896–902 MHz frequencies to transmit. The channel speed can vary from 1600 to 6400 bps, which is enough for text messages — a message can be transmitted or received in less than a second.