Patent GB-524547-A (GB)
Title: Improvements in wide band coupling systems for electric circuits
IPC: H03H7/01
Filed: 1939-04-18
Abstract: 524,547. Impedance networks. HAZELTINE CORPORATION. April 18, 1939, No. 11715. Convention date, April 22, 1938. [Class 40 (iii)] In a circuit, comprising a source coupled to a load, whose admittance is limited by series inductance with or without series or shunt capacitance, a two-terminal or four-terminal network, including a dead-end (resistanceterminated) filter is inserted for the purpose of making the admittance great and of uniform modulus over a wide range of frequencies. The invention is applicable for securing maximum current from a voltage-regulated generator, such as a moving coil, having small resistance and appreciable inductance, or for coupling a current-responsive load to a generator. Thus a generator E 1  of oscillatory voltage, Fig. 1, feeding a current-responsive element I 1 , may have an inductive impedance Ln which, in the absence of the network 7, causes the response at I 1  to be non-uniform. The inductance Lm may be a mid-series terminal arm of a constant -k low-pass filter terminated at Ro by a dead end or resistance which approximately matches its image-impedance characteristic in the pass range ; the filter may have an m-derived midseries or mid-shunt termination at 9, 9. to facilitate matching. The Specification indicates, Fig. 2 (not shown), the effect of giving various values to Ln, and shows that when Ln = ŒLm, the mid-series resistance arm, so that the network has a full-series.or full-shunt termination, the modulus of the admittance of the circuit is approximately constant and equal to Ro. The degree of approximation is impaired by imperfect matching with Ro at the (right-hand) dead end of the filter 7, and can be improved by increasing the number of sections in the filter. The low-pass filter 7 may be replaced by a multi-band filter, or an m-derived section (Fig. 3, not shown) which may be combined with an mm<SP>1</SP> or doubly m-derived terminal section (Fig. 4, not shown). The network may be adapted to an external reactance which includes capacitance in series with the inductance Ln, (Fig. 5, not shown). Instead of being adjacent to one another the source E 1  and receiver I 1  may be located at different points in the resultant network, so that they are separated by a fourterminal portion of it. This arrangement may be used for dealing with an external series inductance, (Figs. 6a, 6c, not shown), or series inductance and shunt capacitance, (Figs. 7a, 7c, not shown), or vice versa, (Figs. 8a, 8c, not shown). In further examples (1) a generator is connected through a constant -k section to a receiver which in turn is connected through a second constant -k' section to a terminating resistance, Fig. 9 (not shown), (2) constant - k low-pass section coupling a generator to a load is arranged in conjunction with an mderived dead-end section so as to complement a series capacitance, Fig. 10 (not shown) or both series capacitance and series inductance, Fig. 11 (not shown). The Specification tabulates the impedance properties of various combinations of television and audiofrequency transmitters and receivers so that the appropriate embodiments of the invention may be selected. Specifications 475,490, 524,548 and 524,549 are referred to.