CHAPTER 2 - Conveying Power at Radio Frequency
32
This means that, at any instant in time, the signal that we observe at the generator end V
S
, and the
signal at the end of the power line V
L
, have a very little phase difference. This is shown in Figure
2.2-2.
Figure 2.2-2 Phase Difference between Generator and Load Signals for a 100km power line
This small phase difference over such a large distance is due to the fact that the speed at which our
signal changes is much lower than the speed at which is propagates.
However, if we made our transmission line much longer, then we would increase the phase
difference between V
S
and V
L
considerably. If, for instance, our line was of such a length that, by the
time the signal appeared at the load end, the generator's signal had gone through a quarter of its
period, we would see a 90⁰ phase shift between V
S
and V
L
at any instant in time.
This is shown in Figure 2.2-3.
Figure 2.2-3 Phase Difference between Generator and Load Signals for a 1500km power line
To find the length over which our signal suffers a 90⁰ delay, we simply need to multiply the speed of
light by a quarter of the period as shown by equation (2.2-1).
Conquer Radio Frequency
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