Guard's Train Radio Interface (GTRI)

The scope was to provide an extra audio channel throughout the train for the guard to be able to monitor the radio communication between the driver and the train controller. Due to the lack of trainlines, the audio from the radio is superimposed on an 200 kHz FM modulated carrier, which then is applied to the “normal” audio trainline in the driver’s cab and then received and demodulated in the guard’s cab.


In addition, the GTRI provides functionality for the train controller to make public announcements via the onboard PA system and for a passenger to communicate with the train controller via the passenger emergency intercom.

Main features:
In total, 5 microcontrollers were used, one master and four slaves,
communicating via the I2C bus. The purpose of the slaves is to provide
additional digital I/O.
The 200 kHz carrier is derived from the master microcontroller and modulated/demodulated with phased locked loops.
The unit provides audio to a separate speaker for the monitor function.

Outcome of the project:
8 trial units were built and they were extensively tested, together with modified radio equipment, on two trainsets (V-set and Tangara). All the specified functions were proved to be working. However, the project appears to been abandoned in favour of the future digital radio system.