GB514997A - Improvements in or relating to resistance elements - Google Patents

Abstract

514,997. Impedance networks. COLLARD, J. May 12, 1938, No. 14133. [Class 40 (iii)] In a network, e.g., an attenuator, that is required to have constant impedance over a wide frequency range and comprising resistances that exhibit shunt capacity C and inductance L at high frequencies, the effect of such capacity and inductance is eliminated by a suitable relationship between L, C and R and by making L/R the same for all such resistance elements. In particular L/C=¢R<2> and reactive elements are added to produce substantially pure resistance. Fig. 1 is a section of the attenuator of Specification 362,472, but A and B at high frequencies can be represented by Fig 2, having L and C. By making L/R the same for all resistances and L/C =¢R<2> (as by adding parallel capacity) the network is designed to have substantially constant attenuation. Since the characteristic impedance of the network is no longer resistive, the input should be shunted by the network of Fig. 3, the elements L, C being chosen to give a resistive impedance in conjunction with the attenuator. Where R, Fig. 3, itself exhibits inductance and capacity, C and L must be modified in value, Fig. 4 (not shown). The resistances may have reactive impedances added to render them independent of frequency, e.g., RLC, Fig. 5, may be in series with R and L or in series with LC, Fig. 6, or a network such that Z1Z2=R<2>, Fig. 7, may be added. Stray shunt capacity of leads may be eliminated by. adding series inductance Figs. 8, 9, 10 (not shown).