3-84. This final equation is used for finding the time required for a voltage

change to travel a unit length, because L and C are given in terms of unit

length. The velocity of the waves may be found by the following equation,

where D is the physical length of a unit:

D

D

v=

Or v =

T

LC

3-85. This is the rate at which the wave travels over a unit length. The units

of L and C are henrys and farads, respectively. T is in seconds per unit length

and V is in unit lengths per second.

3-86. As previously discussed, an infinite transmission line exhibits a definite

input impedance. This impedance is the characteristic impedance and is

independent of line length. The exact value of this impedance is the ratio of

the input voltage to the input current. If the line is infinite or is terminated

in a resistance equal to the characteristic impedance, voltage and current

waves traveling the line are in phase. Recall the following equations:

ET = LI

IT = CE

To determine the characteristic impedance or voltage-to-current ratio, use the

following procedure:

Divide the equations:

ET = LI and IT = CE

ET

LI

=

IT

CE

E

Multiply the result by

I

E2T

LIE

=

I2T

CEI

Simplify:

E2

L

=

I2

C

Take the square root:

E

L

=

= Z0 (characteristic impedance)

C

I

3-87. A problem using this equation illustrates how to determine the

characteristics of a transmission line.

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