Coaxial Impedance Standards

The "mile of standard cable" was for a long time the basis for rating the transmission qualities of telephonic apparatus and networks. 1 , 2 The title of this paper suggests that a return to the old standard has been accomplished. This is true in a restricted sense, but with important differences. The standards here described consist of varying lengths of a rigid coaxial transmission line structure. Their sole function is to supply primary references of resistance, inductance, capacitance and conductance which are numerically comparable to typical unknowns encountered in laboratory cable measurements. Unlike the mile of standard cable, the rigid coaxial is simple structurally, its physical constants and dimensions may be determined accurately, and precise formulae are available for translating these properties into electrical constants at any frequency. It is thus an excellent means for the objective--calculable radio-frequency laboratory standards of R, L, G, and C of the restricted numerical range needed to calibrate the bridge networks used in measurements on the short lengths of cable available to the cable development engineer. Because developmental cables are not usually available in the longer lengths on which the secondary constants of attenuation, phase, and characteristic impedance may be measured directly, laboratory measurements on a cable sample are usually confined to determination of the four distributed primary parameters or constants. From these the secondary constants may then be calculated.