GB583873A - Improvements in electric impedance networks - Google Patents

Abstract

583,873. Impedance networks. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. April 21, 1944, No. 7481. [Class 40 (iii)] [Also in Groups XXXV and XXXVI] The attenuation or phase constant of a fourterminal network is varied, while its characteristic impedance remains constant or varies according to a desired law, by axially shifting an inner set of conductors' with respect to an earthed outer sheath, the inductances and capacitances of the network being thereby simultaneously modified. A low-pass . filter or delay network comprises series inductance residing in coils 3 and shunt capacity between inner and outer cylindrical conductors 4<1>, 2, the outer conductors 2 projecting inwards from the earthed outer screen 1. The coils 3 and condenser plates 4<1> may be carried by an ebonite rod 5 with screwthreaded end members 8, 8<1>, so that rotation of the outer screen 1 causes relative axial movement. The coils 3 ma,y be varied in pitch and diameter so that the inductance, as affected by coupling with the annular closed conductors 2, varies with axial movement according to any desired law, and the condenser plates 3 may be shaped for a similar purpose. Preferably, the ratio L /C and consequently the nominal impedance is held constant while the product LC and consequently the cut-off frequency is varied. The termination may be mid-series or mid-shunt, Figs. 3, 4 (not shown). For very high frequencies, the coils may be replaced by straight strips of foil which may be shaped.