In a simple charged transmission-line pulse generator (animation, right) a length of transmission line such as a coaxial cable is connected through a switch to a matched load "R"L at one end, and at the other end to a DC voltage source "V" through a resistor "R"S, which is large compared to the characteristic impedance "Z"0 of the line. When the power supply is connected, it slowly charges up the capacitance of the line through "R"S. When the switch is closed, a voltage equal to "V"/2 is applied to the load, the charge stored in the line begins to discharge through the load with a current of "V"/2"Z"0, and a voltage step travels up the line toward the source. The source end of the line is approximately an open circuit due to the high "R"S, so the step is reflected uninverted and travels back down the line toward the load. The result is that a pulse of voltage is applied to the load with a duration equal to 2"D"/"c", where "D" is the length of the line, and "c" is the propagation velocity of the pulse in the line. The propagation velocity in typical transmission lines is within 50% of the speed of light. For example, in most types of coaxial cable the propagation velocity is approximately 2/3 the speed of light, or 20 cm/ns.