3-26This final equation is used for finding the time required for a voltage change to travel a unit length,since L and C are given in terms of unit length. The velocity of the waves may be found by:Where: D is the physical length of a unitThis is the rate at which the wave travels over a unit length. The units of L and C are henrys andfarads, respectively. T is in seconds per unit length and V is in unit lengths per second.DETERMINING CHARACTERISTIC IMPEDANCEAs previously discussed, an infinite transmission line exhibits a definite input impedance. Thisimpedance is the CHARACTERISTIC IMPEDANCE and is independent of line length. The exact valueof this impedance is the ratio of the input voltage to the input current. If the line is infinite or is terminatedin a resistance equal to the characteristic impedance, voltage and current waves traveling the line are inphase. To determine the characteristic impedance or voltage-to-current ratio, use the following procedure: