It was already known before that there was still development on POCSAG paging at the east side of our borders. And because there were very promising descriptions on the website of Aachen University (RWTH) PD1AEF and PE2KMV decided to cross the border on April 19th. It the Institute of High Frequency Technology we’ve received a friendly welcome by Ralf DH3WR, one of the drivers of the new development.
In a tour across different rooms and with a lot of questions and answers we’ve gained knowledge about the stunning simplicity of the hardware and the ingenious new software running the new paging network. Hardware has been reduced to a single Raspberry Pi with a PTT circuit and of course a transmitter at 439.9875 MHz (with 4.5 kHz deviation). This RPi runs Raspbian and the application ‘Unipager’. At the background Unipager connects to a core server and is the driver for the transmitter. At the front site Unipager offers a (local) webpage to do some basic configuration and enables direct entry of (test) messages.
The core server is part of the bigger picture. Multiple transmitter sites log in to a core server acting as a central part to connect all the different transmitters. The core system manages user accounts, transmitter groups, message rubrics and time slots. Via the Unipager interface you can send (test) messages using the local transmitter. But the core webpage gives the option to use other transmitter sites or groups of transmitter sites. By grouping transmitters a basic filtering of messages can be done and messages can be directed into certain geographical areas. As an example it’s not usefull to transmit a dutch local weather bulletin via all transmitters in Germany.
The real power of the new german pagernetwork is hidden in the possibility to send messages from (nearly) every thinkable source via an API to the core server to be transmitted via (selected) transmitter groups. This offers the opportunity to keep the existing dutch application (for instance the propagation warning by PE1ITR).
Because of our enthusiasm Ralf DH3WR immediately offered to create accounts for us so we could start straight away. The installation of Linux based applications is nowadays a walk in the park thanks to Github and Debian repositories. The Arduino hardware was disconnected and the old ‘GASCOP’ Slice of Pi was dug up. Because the Unipager application delivers a different waveform than Gascop, the opamp at the Slice of Pi PCB had to be removed. Instead input and output on the socket got connected a bit unconventionally by a jumper wire.
The RTL dongle at the picture above is not related to the DAPNET configuration: the same Pi also acts as ADS-B receiver.
At the same day of the Aachen visit PD1AEF and PE2KMV had their POCSAG transmitters running and were linked to the German network!