Characteristic Impedance

Question 1

Opposition to the transfer of energy in a cable, measured at the input when its length is infinite

Answer 1

characteristic impedance (Zo)

Also known as surge impedance and intrinsic impedance.

Question 2

What does it mean if a line is terminated in its Zo?

Answer 2

The line is called non-resonant, resistive, or flat line.

Question 3

In a lossless transmission line, how are voltage (V) and current (I) related?

Answer 3

V and I are constant in phase.

Question 4

How do V and I behave in a line with loss?

Answer 4

They are reduced exponentially.

Question 5

What is the formula for characteristic impedance (Zo) of a transmission line?

Answer 5

Zo = Z / Y

Where Z is series impedance and Y is shunt admittance.

Question 6

What does the formula Zo = (R + jωL) / (G + jωC) represent?

Answer 6

The characteristic impedance of a transmission line.

Question 7

What is the nature of Zo for a purely resistive line?

Answer 7

Zo = RL

Question 8

What is the nature of Zo for a purely inductive line?

Answer 8

Zo = 0 + jωL

Question 9

What is the nature of Zo for a purely capacitive line?

Answer 9

Zo = 0 - jωC

Question 10

What is the significance of the propagation constant (δ)?

Answer 10

It determines the variation of current and voltage with distance along a transmission line.

Question 11

What does α represent in the propagation constant?

Answer 11

Attenuation constant (dB/uL, Neper/uL)

Question 12

What does β represent in the propagation constant?

Answer 12

Phase shift / phase delay constant (˚/uL, rad/uL)

Question 13

What is the formula for time delay (td) in a transmission line?

Answer 13

td = L * C

Question 14

What happens when a signal reaches the load in a transmission line?

Answer 14

Signals may be totally absorbed, partially absorbed, or not absorbed (total reflection).

Question 15

The relationship of the reflected signal to that of the incident signal.

Answer 15

reflection coefficient (Γ)?

Question 16

What is the range of values for the reflection coefficient (Γ)?

Answer 16

-1 ≤ Γ ≤ 1

Question 17

What is the characteristic impedance of a matched line?

Answer 17

Zo = ZL and Γ = 0

Question 18

What is the characteristic impedance for a short-circuited line?

Answer 18

Zo = 0 and Γ = -1

Question 19

What is the characteristic impedance for an open-circuited line?

Answer 19

Zo = infinite and Γ = 1

Question 20

What is the equation for the standing wave ratio (SWR)?

Answer 20

SWR = (1 + |Γ|) / (1 - |Γ|)

Question 21

What happens to the voltage in a mismatched line?

Answer 21

There will be maximum and minimum voltage.

Question 22

How is the impedance of an infinitely long section of cable determined?

Answer 22

Using the characteristic impedance of the cable.

Question 23

What two parameters are used to calculate the time delay in a delay line?

Answer 23

Inductance and capacitance.

Question 24

What is the formula for the propagation speed (V) in a transmission line?

Answer 24

V = 1 / √(LC)

Question 25

What parameters are needed to find the characteristic impedance of a coaxial line?

Answer 25

* Inside diameter of the outer conductor * Diameter of the inside conductor * Dielectric constant

Question 26

What does the term 'electrical length' refer to?

Answer 26

The length of a transmission line in relation to the wavelength of the signal.

Question 27

Fill in the blank: The characteristic impedance for a balanced transmission line is calculated with the formula Zo = _____

Answer 27

√(L/C)