The use of surface acoustic wave devices for a European train control system (ETCS) as a stationary transponder is shown. The Surface Acoustic Wave (SAW)-device in such a system acts as a local coherent oscillator for the balise. We show the design and analysis of the dynamically programmable SAW delay line. We use one single phase unidirectional transducer (SPUDT) for coupling the electromagnetic wave received by an antenna to the acoustic wave and vice versa. (For the test system we built a tag with 8 switchable reflectors and one additional fixed reflector as reference bit.) The switchable reflectors are designed as split finger transducers which are connected via bond wires to hybrid circuitry. This circuitry consists of capacitors and inductors for matching, and GaAs-FETs for switching. Measurements with this programmable hybrid SAW-delay line show dynamic range of 25 dB between “ON” and “OFF” reflectors with good reproducibility