GB502615A - Improvements in or relating to electric wave filters for thermionic valve amplifiers and the like - Google Patents

Abstract

502,615. Impedance networks. PERCIVAL, W. S. Sept. 22, 1937, No 25698. Addition to 475,490. [Class 40 (iii)] A filter comprises a plurality of half-sections of different type which are matched over the pass-band, and terminated at one end by the characteristic impedance and having at the other end an impedance equal to a full shunt reactance, so that the impedance at that end is constant over the pass-band. The invention is approached from a filter (according to the parent Specification) having identical halfsections, Fig. 1a, and terminated by a full shunt reactance C, D. The sections A, B are replaced by a low-pass filter E, Fig. 2, and preferably, the band-pass of the whole network is the upper two-thirds of the range of the low-pass filter E; a slight mis-match between sections E, F is compensated by varying 13, 14 or by raising the impedance of E. In modifications, the half-sections B, C, Fig. 1a, may be replaced by M-derived half-sections from which the series capacities have been eliminated, giving a # arrangement cf inductances 15, 16, 17, Fig. 4; the # arrangement of inductances may be replaced by a T, and the constant-k halfsection A of Fig. 1a by a low-pass filter L, Fig. 5; the constant low-pass filter L of Fig. 5 may be replaced by a mid-shunt termination M, Fig. 6; and the T connected inductances of Fig. 6 may be replaced by a # connection, Fig. 9 (not shown). The capacities of the network are preferably the inter-electrode capacities of associated valves, Fig. 8 (not shown. Transformers may be incorporated in the network to enhance the effect of low interelectrode capacities if desired, Fig. 11 (not shown). The filters according to the invention have the advantage of fewer tuned circuits than the filter of, e.g. Fig. 1a.