RinZo2/Rout752/1005625/10056ΩProblem 18-6An antenna is known to have a pure resistance of 600 Ω. You want to match it to 50.0 Ωpure resistance. What is the characteristic impedance needed for a quarter-wavematching section?Use this formula:Zo2RinRoutZo26005030,000Zo2(30,000)1/2173ΩThe challenge is to find a line that has this particular Zo. Commercially manufacturedlines come in standard Zo values, and a perfect match might not be obtainable. In thatcase, the closest obtainable Zo should be used. In this case, it would probably be 150 Ω.If nothing is available anywhere near the characteristic impedance needed for aquarter-wave matching section, then a coil-type transformer will probably have to beused instead. A quarter-wave matching section should be made using unbalanced line ifthe load is unbalanced and balanced line if the load is balanced.The major disadvantage of quarter-wave sections is that they work only at specificfrequencies. But this is often offset by the ease with which they are constructed, if ra-dio equipment is to be used at only one frequency, or at odd-harmonic frequencies.What about reactance?Things are simple when there is no reactance in an ac circuit using transformers. But of-ten, especially in radio-frequency circuits, pure resistance doesn’t occur naturally. It hasto be obtained by using inductors and/or capacitors to cancel the reactance out.What about reactance?34118-11A quarter-wave matching section of transmission line.Abbreviations are discussed in the text.