TC 9-64 _________________________________________________________________________
transmission line. Thus, the behavior of a finite line may be quite different
from that of the infinite line.
Reflection of DC Voltage from an Open Circuit
3-90. The equivalent circuit of an open-ended transmission line is shown in
figure 3-24, view A. Again, losses are to be considered as negligible, and L is
lumped in one branch. Assume that (1) the battery in this circuit has an
internal impedance equal to the characteristic impedance of the transmission
line (Zi = Z0); (2) the capacitors in the line are not charged before the battery
is connected; and (3) because the line is open-ended, the terminating
impedance is infinitely large.
3-91. When the battery is connected to the sending end as shown in figure 3-
24, view A, a negative voltage moves down the line. This voltage charges each
capacitor, in turn, through the preceding inductor. Because Zi equals Z0, one-
to E/2 (view B). When the last capacitor in the line is charged, there is no voltage
across the last inductor and current flow through the last inductor stops. With no
current flow to maintain it, the magnetic field in the last inductor collapses and
forces current to continue to flow in the same direction into the last capacitor.
Because the direction of current has not changed, the capacitor charges in the
same direction, thereby increasing the charge in the capacitor. Because the
energy in the magnetic field equals the energy in the capacitor, the energy
transfer to the capacitor doubles the voltage across the capacitor. The last
capacitor is now charged to E volts and the current in the last inductor drops to
zero.
3-28
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