Assume that the line shown in figure 3-23 is 1,000 feet long. A 100-foot

(approximately 30.5 meter) section is measured to determine L and C. The

section is found to have an inductance of 0.25 millihenry and a capacitance

of 1000 picofarads. Find the characteristic impedance of the line and the

velocity of the wave on the line. The characteristic impedance is--

Z 0 = LC

-3

0.25x10

Z0 =

-12

1000x10

6

Z 0 = 0.25x10

Z 0 = 0.5x10

3

Z 0 = 500Ω

If any other unit length had been considered, the values of L and C would be

different, but their ratio would remain the same as would the characteristic

impedance.

The formula for T is:

T = LC

-3

-12

T = 0.25x10

x1000x10

-12

T = 0.25x10

-6

T = 0.5x10

second

T = 0.5 microsecond

The formula for the velocity of a wave is:

D

V=

T

100 feet

V=

-6

0.5x10

second

6

V = 200x10 feet/second

V = 200,000,00 0 feet/secon d

3-88. Transmission line characteristics are based on an infinite line. A line

cannot always be terminated in its characteristic impedance because it is

sometimes operated as an open-ended line and at other times as a short-

circuit at the receiving end. If the line is open-ended, it has a terminating

impedance that is infinitely large. If a line is not terminated in characteristic

impedance (Z0), it is said to be finite.

3-89. When a line is not terminated in characteristic impedance, the incident

energy is not absorbed but is returned along the only path available--the