For the continuous signal an analogue bandpass filter is applied to isolate the range of TVM frequencies between 1,600–2,640 Hz. Within this, each of the four 1,700/2,000/2,300/2,600 Hz carrier-frequencies are tested for the presence of a frequency-modulated 25.68 Hz signal. The 25.68 Hz signal is necessary for the track-circuit function and for the activation of relays within the train TVM430 equipment. The data bits themselves are frequency modulated at 0.64 Hz intervals between 0.88 Hz and 17.52 Hz.
