Key Topic 66: Transmission Lines

Question 1

3-66J1: What is the meaning of the term velocity factor of a transmission line?

A. The ratio of the characteristic impedance of the line to the terminating impedance.
B. The velocity of the wave on the transmission line divided by the velocity of light in a vacuum.
C. The velocity of the wave on the transmission line multiplied by the velocity of light in a vacuum.
D. The index of shielding for coaxial cable.

Answer 1

B. The velocity of the wave on the transmission line divided by the velocity of light in a vacuum.

Question 2

3-66J2: What determines the velocity factor in a transmission line?

A. The termination impedance.
B. The line length.
C. Dielectrics in the line.
D. The center conductor resistivity.

Answer 2

C. Dielectrics in the line.

Question 3

3-66J3: Nitrogen is placed in transmission lines to:

A. Improve the “skin-effect” of microwaves.
B. Reduce arcing in the line.
C. Reduce the standing wave ratio of the line.
D. Prevent moisture from entering the line.

Answer 3

D. Prevent moisture from entering the line.

Question 4

3-66J4: A perfect (no loss) coaxial cable has 7 dB of reflected power when the input is 5 watts. What is the output of the transmission line?

A. 1 watt.
B. 1.25 watts.
C. 2.5 watts.
D. 5 watts.

Answer 4

A. 1 watt.

Question 5

3-66J5: Referred to the fundamental frequency, a shorted stub line attached to the transmission line to absorb even harmonics could have a wavelength of:

A. 1.41 wavelength.
B. 1/2 wavelength.
C. 1/4 wavelength.
D. 1/6 wavelength.

Answer 5

C. 1/4 wavelength.

Question 6

3-66J6: If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot transmission line fed by a 100 watt transmitter?

A. 70 watts.
B. 50 watts.
C. 25 watts.
D. 6 watts.

Answer 6

D. 6 watts.