3-53. The impedance presented to the input terminals of the transmission

line is not merely the resistance of the wire in series with the impedance of

the load. The effects of series inductance and shunt capacitance of the line

itself may overshadow the resistance, and even the load, as far as the input

terminals are concerned.

3-54. To find the input impedance of a transmission line, determine the

impedance of a single section of line. The impedance between points K and L,

in figure 3-16, view B, can be calculated by the use of series-parallel

impedance formulas, provided the impedance across points M and N is

known. But because this section is merely one small part of a longer line,

another similar section is connected to points M and N. Again, the impedance

across points K and L of the two sections can be calculated, provided the

impedance of the third section is known. This process of adding one section to

another can be repeated endlessly. The addition of each section produces an

impedance across points K and L of a new and lower value. However, after

many sections have been added, each successive added section has less and

less effect on the impedance across points K and L. If sections are added to