Experimental Test of Propagation-Parameter Calculations for Shielded Balanced Pair Cables

A method for calculating propagation parameters of uniform cables is presented in Ref. 1. The method depends on algorithms for determining the charge densities on the wires and shield, and this is presented in Ref. 2. For the shielded balanced pair (SBP) in particular, a computer program has been written to carry out the required calculations. To test the method, three different SBP cables were fabricated and, with the cables laid straight, their attenuation and phase-shift per length were measured over a broad range of frequencies and then compared with calculated values. The results of this experimental test are presented in this paper. The three cables were constructed to conform to the SBP model. In this model, the two wires are identical, they are straight and parallel, and they are symmetrically located inside a cylindrical, metallic shield of uniform thickness. Also, the dielectric material separating the wires and shield is homogeneous and isotropic. A cross section of an ideal SBP is shown in Fig. 1. The first cable is an untwisted version of a standard twisted-pair cable built by Western Electric, called the 754E. This cable deviates somewhat 627