What is the meaning of the term velocity factor of a transmission line?

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

The speed of radio waves through a substance is compared to the speed of light in a vacuum, to see the effect of the material on the speed--how much slower. It is called "velocity factor," or a speed of the radio wave propagation.

For more information, please see Wikipedia's article Velocity Factor.

Also, see Electronics Notes site for the article Coax Cable Velocity Factor

Last edited by markadlerdallas. Register to edit

Tags: none

What determines the velocity factor in a transmission line?

(C).   Dielectrics in the line.

The dielectrics is a material that does not let electrical current easily or completely. Can be actually an insulator.

See Wikipedia's article Dielectric

The speed of radio waves through a substance is compared to the speed of light in a vacuum, to see the effect of the material on the speed--how much slower. It is called "velocity factor," or a speed of the radio wave propagation.

For more information, please see Wikipedia's article Velocity Factor.

Also, see Electronics Notes site for the article Coax Cable Velocity Factor

Last edited by markadlerdallas. Register to edit

Tags: none

Nitrogen is placed in transmission lines to:

(D).   Prevent moisture from entering the line

For more information, please see Terra Universal site for the Why use nitrogen to purge moisture?

Also, see Electronic Design site for the article Nitrogen Purging: Manufacturers Eliminate Moisture from Optoelectronic Systems

Last edited by markadlerdallas. Register to edit

Tags: none

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.

The reflected power is the returning of radio signal due to mismatch of the resistance between the transmitter and the antenna. The reflection is measured in dB's, which are on the logarithmic scale--the loss in decibels.

The Effective Radiated Power (Watts) is
ERP = Input power (Watts) X Antenna gain

Since the antenna is a passive device, the output must always be less than the input. Here, however, we are given a 7 dB reflective power, identifying SWR problem.

• dB = 10 log Power Output /Power Input
  but this is for gain calculation =
  

for loss, dB = 10 log (-) Power Output/Power Input

• (-) 7 dB = 10 log (-) 1 Watt/5 Watts
  thus Power Output is 1 Watt

For more information, please see the Mouser site for the pdf document Antenna Basic Concepts

Please see the following calculators:

• Antenna CA calculator Effective Radiated Power (ERP)
  
• All About Circuits Friis Transmission Calculator
  

Last edited by markadlerdallas. Register to edit

Tags: none

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

(C). 1/4 wavelength

For more information, please see Ibiblio site for the well-illustrated Chapter 14 TRANSMISSION LINES

Please see the following calculators:

• Antenna CA calculator Effective Radiated Power (ERP)
  
• All About Circuits Friis Transmission Calculator
  

Last edited by markadlerdallas. Register to edit

Tags: none

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?

(D).   6 watts.

Please see the following calculators:

• Antenna CA calculator Effective Radiated Power (ERP)
  
• All About Circuits Friis Transmission Calculator
  

Last edited by markadlerdallas. Register to edit

Tags: none