Four level FSK interface

for pager data decoding

With this interface and decoding software, you can decode ERMES, FLEX, POCSAG and some other pager systems (not only pagers, depending on used SW). This interface is not new, but is redesigned to more professional form. You need only +5 V for power supply easily available from keyboard or PS/2 connector or somewhere from PC (or directly from scanner). Voltage inverter on board make necessary negative voltage. On input is trimmer for setting sensitivity.

FLEX, POCSAG, ACARS, MOBITEX, ERMES
Software required: PDW

FLEX, POCSAG frequencies: 138 - 174MHz, 279 - 286MHz, 929 - 932MHz
Software required: WINFLEX v.1.0

ERMES frequencies: 169.400 - 169.825 MHz
Software required: ERMES v.4c (source code included)

Picture from PDW decoding program (confidential parts illegible)

Interface construction details

Schematic diagram:

Signal response picture:

On first picture is showed response on signal from generator (100 mVp sinus @ 1 kHz) measured on outputs at serial connector. Second picture is response on real 4-level ERMES signal from my scanner.

Component placing and PCB pictures:

PCB size is 68 x 33 mm (print in 300DPI)

And pictures of real interface:

Construction notes:

- Component holes are 0.8 mm, for trimmer and screw terminals 1.0 mm
- Interface need signal output from discriminator !
- There are four wire bridges on board, solder before IC's !