Standalone prototype of a POCSAG base station:
Linksys NSLU2 computer on the right, Debian Linux installed on the 512M USB memory stick, cheap USB hub and USB serial adapters from DealExtreme, connected to the Internet using a Siemens GPRS module (on top of Motorola radio, flat-rate multi-SIM data). Dials up automatically when powered on and redials the connection if it drops.
POCSAG modem in the top right corner, Atmel microcontroller, original design by N2RVQ. Motorola GM340 transceiver transmitting on 144.975 MHz.
ATI Wireless Corporate programmable pager receiving the paging messages and saying "beep". There's another receiver (FT-7800) on the background monitoring the 512 bps (yes, bits per second) transmissions.
The tiny computer runs a transmitter client, which polls a pair of central servers for new messages which should be transmitted. Another server runs a DX cluster client which uploads DX spots using an HTTP JSON API to the servers. The servers authenticates both the transmitter clients and the message sources using HMAC-SHA1.
http://oh7lzb.blogspot.com/2010/03/project-pocsag-paging-network.html
