POCSAG & FLEX pager decoding

Web Page Last Updated: 9 MAY 98

Latest program revision: 0.005
See note at bottom of page about future updates.

General Description

This page describes how to receive POCSAG & FLEX pager messages on your PC type computer with a radio scanner and an appropriate interface circuit hooked to your serial port. The basic idea is that your interface causes a stream of serial port interrupts that represents the incoming paging data stream received on your scanner. The receive program (which runs only under DOS) examines this interrupt stream in order to reconstruct the paging data and show the transmitted messages on the screen (or put them in a log file). The program currently supports POCSAG, FLEX, and to some extent ReFLEX modes.

A more precise description of program features, functions, revision history, and problems can be found in the program information section.

The program can run with either a simple single op-amp 2 level FSK interface (Hamcomm type) or a more complicated 4 level FSK interface. More details can be found in the interface information section. The Hamcomm type interface is commercially available, and is used by quite a number of commercial & shareware programs to receive all kinds of digital traffic. If you are a radio hobbyist then there is a good chance you already have such a Hamcomm type interface sitting around; if not it is very easy to build one yourself. The Hamcomm interface will allow you to test this program without having to go to the trouble of building of the 4 level FSK interface. The only disadvantage is that you will completely miss FLEX messages transmitted on phases B & D.

Finally, take a look at the flex information section if you would like to find out more about the FLEX protocol.

If you decide you like what you see, click POCFLEX.ZIP (about 115k) to download a ZIP package. This package contains copies of the web pages on this site (they serve the function of a manual), the interface schematic GIF files, the program source code (written using Borland C++), and an executable version of the program. That should be all the information you need to start receiving FLEX messages on your own.

Note: this program is freeware. That means absolutely free; there is no "registered version"; and I as the author don't want your money.

Legal Stuff

Caution: It is your responsibility to be aware of and in compliance with any laws concerning the interception of radio messages in your country.

FLEX and ReFLEX are Motorola trademarks.


I would like to thank everyone who has sent in suggestions, information, or pointed out what I've screwed up in the program. In particular I would like to thank the person who pointed out U.S. Patent #5555183 to me, and I would also like to thank the person who explained how to derive the correct POCSAG capcodes.

Send me Mail

(While I still know how my program works)

Future Updates

I am guessing that future program updates will occur a lot less frequently now that the worst program bugs have been found. What the program really needs now is an extensive rewrite in order to add new features (such as allowing you to scroll back through received messages). Additionally, I also want to put up some more digital scanning related information on this web page. With all of this it may take a few weeks (or longer) to get POCFLEX version 1.0 done. I'm sure you don't want to keep looking at this page, so I'll post a message to rec.radio.scanner when version 1.0 comes out.