GB528133A - Phase-correcting low-pass electric wave filters - Google Patents

Abstract

528,133. Impedance networks. HAZELTINE CORPORATION. April 27, 1939, No. 12691. Convention date, May 18, 1938. [Class 40 (iii)] In a phase-correcting network, the phase shift is a multiple of # at selected points in the working range; the phase characteristic is approximately linear except in the neighbourhood of the cut-off frequency; the network is terminated by shunt capacitance, so that it may be used in conjunction with the interelectrode capacity of a thermionic valve; and there is a small negative mutual inductance between elements of the filter. The low-pass network shown in Fig. 1b, in which the series inductances L, L have mutual inductance M, is equivalent to two constant-k half-sections having mid-shunt outer terminations and separated by an m-derived tee section with negative inductance in the shunt arm, Fig. la (not shown). In the m-derived section, m is chosen to be greater than 1, and the phase lag is 2 # at the cut-off frequency and # at an intermediate frequency dependent on m. The use of two m-derived sections, Fig. 1d (not shown) gives a phase shift which is a multiple of # at two selected frequencies in the pass range, and a similar result is given by the network shown in Fig. 2A, where the inductances L1, L1 are mutually coupled. The inductance 45 may be omitted if the two selected frequencies are suitably rotated. The inductance L2 may be coupled to L1, L1, Fig. 3a (not shown). A valve 10, Fig. 4, having interelectrode capacitance represented in two parts 12, 13 may be coupled to a valve 11, whose input capacitance is represented at 14, 15, through a circuit equivalent to that shown in Fig. 1 b and comprising inductances 18, 19 corresponding to L, L, while the parts 13, 14 of the interelectrode capacitances correspond to Cl, Cl and the capacitance 20, corresponding to C2, comprises at least in part the capacitance between the inductances and earth. The mutual inductance M is provided by a link circuit 21. The input shunt impedance of this coupling is maintained by a dead-end filter 12, 16, 17, 26 of the kind described in Specification 524,548. A grid leak resistance 22 and blocking condensers 23, 24 are provided.