The development of a precision termination for 0.375-inch polythene-disc-insulated coaxial cable

The uses of a precision termination (simulator) in pulse and bridge testing of disc-insulated coaxial cable are outlined and related to the accuracy of match required. A procedure to determine the average cable impedance law with sufficient exactness is described, and a known approximation is used both to illustrate this law and to discuss the departure of local cable impedances from the average. Thus the adjustment facilities necessary in a practical simulator are determined. Details are given of some theoretical networks having the required response, and the course of development from a first laboratory circuit to final prototype is indicated. The measured responses are discussed and the significance of various amendments to the circuit values to achieve the highest accuracy is explained. It is concluded that the design is well suited to the general requirements of pulse testing and to the accurate determination of end impedances to about 0.05 ohm. In bridge testing, similar accuracies in both real and imaginary parts may be obtained between 50 kc/s and 8 Mc/s.