Some time ago the block diagram above was the result of an hour thinking and scribbling. Aim is to create an Echolink node via Tetra. In fact it’s not a big deal to connect a DMO mode Tetra radio via an interface to the internet. Much bigger is the challenge to let the Tetra set connect to a node of your choice. Because it’s not possible to send DTMF via Tetra (in DMO). Unfortunately Echolink needs DTMF to accept commands.
But Tetra offers another option: Peripheral Equipment Interface, also known as PEI. A Tetra radio pushes out a lot of data via the serial interface. So theoretically this could offer an opportunity. If it’s possible to capture ‘SDS’ messages (Short Data Service) at the PEI interface, for example an Arduino board could turn this into a DTMF tone. And that DTMF tone can then be injected into the analog sound stream to provide the correct commands for Echolink. In that case SVXLink at a Raspberry Pi as node application offers great possibilities.