Assessment of coaxial cable for frequency-division-multiplex transmission by means of a c.w.-burst test signal

A c.w.-burst signal is shown to have certain advantages over both pulse and normal c.w. techniques in the testing of coaxial cables intended for long-distance frequency-division-multiplex systems. The burst is made long enough to integrate the effect of reflections over a length of cable, yet sufficiently short to enable connector and termination reflections to be distinguished from those in the cable itself by means of an Ascan oscilloscope display. It is possible, in fact, to measure the v.s.w.r. of any segment of the cable by means of a suitable choice of burst length and observation time. An analysis is presented of the relationship between such a backscattered signal and the perturbation in the forward transmission with systematic irregularities of cable impedance. The effect of jointing practical drum lengths to form a repeater length of cable is discussed, and the analysis is illustrated by reference to the standard 9.5mm cable over the frequency range 10¿100MHz.