Abstract: A resonant circuit for extracting a signal at a bit frequency from a data flow, at a clock frequency lower than microwave frequencies. The circuit has good frequency, selectivity and stability even under varying operative conditions, and in particular at varying temperatures. The circuit includes a G-shaped strip line section, which has an appropriate length to resonate at a predetermined range of frequencies, and is applied on an amorphous quartz substrate. The extraction system includes the above resonant circuit, a data flow input circuit, and an output circuit for amplifying the extracted signal.