Figure 1
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Figure 1 |
At time t = 0 the switch in Figure 1 closes. Sketch the wave form Vo.
The line length, L is 3 meters. The velocity of propagation on the line is the velocity of light 3x108 meters/sec.
Answer
At t = 0 the switch closes and the transmission line looks like a 50 ohm resistor since there is no information about the 75 ohm termination. There is only a forward traveling wave present. At t=0,( and for the first 20 nsec) the input voltage is just due to the forward traveling wave (incident wave). Vo = 5V.The time it takes to travel 3 meters is,
Td = L/v = 3/3x108 = 10 nsec.The reflected wave returns after 20 nSec (round trip delay). The amplitude of the reflection is determined by the reflection coefficient.The reflection coefficient = 0.2. Therefore, 1 V is reflected. (5*0.2) After 20 ns the reflected wave returns and adds to the incident wave. 5+1=6
