FIELD: electronic engineering. SUBSTANCE: filter is built up of two partial filters TF1 and TF2 whose discrimination ratios are variable by means of discrimination-ratio control circuit (CORR), so as to form, for example, approximately inverting filter for time-varying transmission channel which enables both non-decimating mode of operation when polling frequency corresponds to rate of characters and decimating one when polling frequency satisfies count theorem by means of ON/OFF operations. Wiring between ratio multipliers 31-41 of circuits of frequency filters TF1, TF2 and partial correlators 80-90 of ratio control circuit (CORR) is invariant relative to mode-of- operation change-over operations. EFFECT: reduced quantity of switches or selector switches. 2 cl, 2 dwg
