Signal transmission system for a technical installation having a region exposed to radiation, in particular for a nuclear power plant (2) having a containment (6), wherein a modulator (26) for converting an analogue measured value (K), which is provided by an associated sensor (8), into a PWM signal (D) is arranged inside the region exposed to radiation, a demodulator (38) for reconstructing the measured value (K) from the PWM signal (D) is arranged outside the region exposed to radiation, the modulator (26) is implemented using radiation-hardened circuit technology, preferably analogue circuit technology, and comprises an adaptable measured value normalization means (18), a sawtooth generator (14) and a comparator (16), and the demodulator (38) is connected to the modulator (26) via a signal transmission line (34) DC-isolated from the output of the comparator (16).