Applicability of coaxial cables at picosecond range timing

Timing performances of conventional coaxial cables like RG 223 and RG 58 were studied. The effects of timing pulse shape, cable bandwidth, ambient fluctuations and physical stress were as input parameters. Pulse delays and shapes were studied using a time interval counter and a fast digital oscilloscope. Delay as a function of frequency was studied with resonance method and phase delay measurements. Effects of ambient factors and physical stress were studied at a frequency of 5 MHz using a phase comparator capable of resolving 10 fs. The results revealed that conventional tick pulse is not anymore usable below 1 ns if the cable delay has to be well known. Environmental effects may change the cable delay up to 100 ps. Therefore, as a first approximation the pulse shape has to be changed to fit the properties like bandwidth and velocity dispersion of cables. Cos² pulse or RF-burst may help but finally one has to use optical cables.