A sensor measures the current in high frequency pulses (e.g., pulses having fast rise times) that are transported on coaxial transmission lines. The sensor includes an entrance coaxial conductor and an exit coaxial conductor that are interconnected by a continuous inner conductor. The outer conductors of the two coaxial conductors are interrupted and are interconnected by a sensing resistor with a substantially constant resistance. An output sensor coaxial conductor has an inner conductor electrically connected to a first end of the sensing resistor and has an outer conductor connected to a second end of the sensing resistor. Tapered ferrite cores are placed around the three coaxial conductors proximate the connections to the sensing resistor. Preferably, the sensing resistor is a tubular resistor formed on a dielectric cylindrical tube. The sensor is enclosed within a continuous conductive housing.