nt and reflected wave added, while the weakest sound (minimum intensity) occurred where the incident and reflected sound opposed each other. 16 In a properly terminated line, there are no reflections. Vref = 0 and substituting this value into Equation 2.2.37 gives VSWR = CHAPTER 2.2 Transmission lines Example 2.2.9 transmission line. Calculate the reflected power as In Figure 2.2-12, the incident voltage measured along the a percentage of the incident power. transmission line is 100 V and the reflected voltage Given: VSWR = 1.07, Z = 50 S measured on the same line is 10 V. What is its VSWR? Required: Reflected power as a percentage of inci- dent power Solution Using Equation 2.2.37 Solution Using Equation 2.2.38a VSWR = 0.034 Since power is proportional to V2 2.2.11.7 VSWR and reflection coefficient Pref = (0.034)2 x = Pinc = 0.001 Pinc VSWR is related to the voltage reflection coefficient by = 0.1% of Pinc From the answer to Example 2.2.11, you should now VSWR = realise that: a load with an SWR of 1.07 is a good terminating load; (2.2.38) there are hardly any reflections when a transmission line is terminated with such a load; the transmission line is likely to behave like an infi- nitely long line. (2.2.38a) 2.2.11.8 Summary of Section 2.2.11 Example 2.2.10 If a transmission line is not properly terminated, re- What is the VSWR of a transmission system if its re- flections will occur in a line. These reflections can aid or flection coefficient Tv is 0.1? oppose the incident wave. In high voltage lines, it is possible for the aiding voltages to cause line insulation Given: 0.1 breakdown. In high current lines, it is possible at high Required: VSWR current points for aiding currents to overheat or even Solution destroy the metallic conductors. The voltage reflection coefficient () can be calcu- Using Equation 2.2.38 lated by voltage voltage wave wave Perfect match occurs when VSWR = |1 This is the Manufacturers tend to use VSWRs when quoting the im- optimum condition and examination of Equation 2.2.38 pedances as