POCSAG Decoder V2.00

 

2 Hardware

2.2 PC interface

At discriminator output, we get a stream of bits with about ±1 V width. PC can't process this signal. Using the serial port (RS232), we need signal with ±12 V width. This interface makes the signal compatible with RS232 specifications, so the PC can use it.

Here is the diagram, which is in fact the HAMCOM receiver circuit diagram:

HAMCOM Interface - Receive circuit
Fig. 4 - HAMCOM Receiver

Component Value
IC1 LM 741
R1 - R2 100 K
D1 .. D4 1N 4148
C1 0,1 µF
C2 - C3 10 µF 16V

Please, refer to HAMCOM documents for informations about this circuit.


In HAMCOM interface, the signal is directed to DSR. You can direct it to CTS. You can place a switch to select the output between DSR or CTS.

The table below shows the SUB-D connections.

Signal 25 Points 9 Points
TxD 2 3
RTS 4 7
CTS 5 8
DSR 6 6
GND 7 5
DTR 20 4

This simple circuit is the only one you need to receive data. To send data, you need to complete this diagram with at least the FSK diagram. You can make a complete HAMCOM interface if you place the Transmit Audio and PTT diagram.

To receive, the easiest is to make a board you can put in a SUB-D 25 case. Here is an example:

HAMCOM Printed board
Fig. 5 Printed Circuit - Copper side

Use the LM741 size to get the good size if you print this board.

Components are placed like this:

Components placing
Fig. 6 - Components

Notice that I use a Diode Bridge instead of the four diodes.

Here we are. You get all you need to decode POCSAG messages. I hope this program will be useful for you.


For any information, send me an e-mail
Mail megalak@gulliver.fr
Page made by Bernard GALASSO
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