TC 9-64 _________________________________________________________________________
3-73. A plot of these new voltages produces the solid curve shown in
figure 3-22, view B. For reference, the curve from T7 is drawn as a dotted
line. The solid curve has exactly the same shape as the dotted curve, but has
moved to the right by the distance X. Another plot at T9 would show a new
curve similar to the one at T8, but moved to the right by the distance Y.
3-74. By analyzing the points along the graph just discussed, you should be
able to see that the actions associated with voltage changes along an RF line
are as follows:
All instantaneous voltages of the sine wave produced by the generator
travel down the line in the order they are produced.
At any point, a sine wave can be obtained if all the instantaneous
voltages passing the point are plotted. An oscilloscope can be used to
plot these values of instantaneous voltages against time.
The instantaneous voltages (oscilloscope displays) are the same in all
cases except that a phase difference exists in the displays seen at
different points along the line. The phase changes continually with
respect to the generator until the change is 360 degrees over a certain
length of line.
All parts of a sine wave pass every point along the line. A plot of the
readings of an AC meter (which reads the effective value of the voltage
over a given time) taken at different points along the line shows that
the voltage is constant at all points (see figure 3-22, view C).
energy arriving at the end of the line is absorbed by the resistance.
VELOCITY OF WAVE PROPAGATION
3-75. If a voltage is initially applied to the sending end of a line, that same
voltage will appear later some distance from the sending end. This is true
regardless of any change in voltage, whether the change is a jump from zero
to some value or a drop from some value to zero. The voltage change will be
conducted down the line at a constant rate.
3-76. Recall that the inductance of a line delays the charging of the line
capacitance. The velocity of propagation is therefore related to the values of L
and C. If the inductance and capacitance of the RF line are known, the time
required for any waveform to travel the length of the line can be determined.
To see how this works, observe the following relationship:
Q = IT
This formula shows that the total charge or quantity is equal to the current
multiplied by the time the current flows. Also--
Q = CE
This formula shows that the total charge on a capacitor is equal to the
capacitance multiplied by the voltage across the capacitor.
3-77. If the switch in figure 3-23 is closed for a given time, the quantity (Q) of
electricity leaving the battery can be computed by using the equation
Q = IT. The electricity leaves the battery and goes into the line, where a
charge is built up on the capacitors. The amount of this charge is computed
by using the equation Q = CE.
3-24
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