TC 9-64 _________________________________________________________________________
Figure 3-16. Characteristic Impedance
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
3-16
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