GB1219563A - Improvements in or relating to noise reduction insignalling circuits - Google Patents

Abstract

1,219,563. Limiters; interference suppression. SOUND SYSTEMS Ltd. 11 Nov., 1968 [9 Aug., 1967], No. 36580/67. Headings H3T and H4L. A noise suppression arrangement comprises a limiter in which the limiting level is a function of the input signal, coupled to a relatively low-Q frequency selective circuit, followed by an amplitude gate which clips signals below a first level and also above a second level, followed by a relatively high-Q frequency selective circuit; the second clipping level of the amplitude gate is a function of the input signal thereto, but may have a substantially fixed limit (Fig. 1, not shown). The limiter may be of the type described in Specification 1,219,562, in which diodes 4, 5, Fig. 2, are connected back-to-back in the signal path between input terminal 1 and output terminal 7, a signalderived bias being applied to the common terminal A by means of amplifier 10, voltagedoubling rectifiers 11, 12 and smoothing circuit 13, 14, 15. The amplitude gate is a modification of this circuit, in which amplifier 10 is replaced by two amplifiers 17, 18, diodes D1, D2 being connected in the series path between the amplifiers to block the passage of signals below a first level; diodes D3, D4 are connected in shunt with the signal path and shortcircuit it to earth for signals above a second level, the two levels being obtained by suitable choice of diodes.