Characteristic impedance contnd
This presentation is the property of its rightful owner.
Sponsored Links
1 / 23

Characteristic Impedance Contnd. PowerPoint PPT Presentation


  • 69 Views
  • Uploaded on
  • Presentation posted in: General

Characteristic Impedance Contnd. Air Dielectric Parallel Line Coaxial Cable. Where: D = spacings between centres of the conductors r = conductor radius. Velocity Factor. The speed at which an energy is propagated along a transmission line is always less than the speed of light.

Download Presentation

Characteristic Impedance Contnd.

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Characteristic impedance contnd

Characteristic Impedance Contnd.

  • Air Dielectric Parallel Line

  • Coaxial Cable

Where: D = spacings between centres of the conductors

r = conductor radius


Velocity factor

Velocity Factor

  • The speed at which an energy is propagated along a transmission line is always less than the speed of light.

  • Almost entirely dependant upon the dielectric constant

  • Propagation velocity of signal can vary from 66% (coax with polyethylene dielectric) to 95%(air).


Velocity factor and propagation velocity

Velocity Factor and Propagation Velocity


Response of line

Response of Line

  • CONDITIONS

  • Step Impulses

  • Assume lossless line and infinite length with Zo equal to characteristic impedance of the line

  • Discuss:

    -Reflections along a line of finite length that is:

    a.) Open at point of termination (end of line)

    b.) Shorted at point of termination

    c.) Matched load at point of termination


Open circuited line

Open Circuited Line

  • Switch is closed and followed by a surge down line.

  • How much of the source voltage appears across the source? (V/2)

  • What is the state of voltage and current at the end of the line?

  • For what time frame do the initial conditions exist? (2T)

  • What is the relative direction of incident and reflected current?(opposite)


Short circuit line

Short Circuit Line

  • What is the state of voltage at the source prior to 2T? (V/2)

  • What is the state of voltage and current when the surge reaches the load? (V=0 and I depends on system characteristics)

  • What is the direction of incident and reflected current? (same)


Pulse input to transmission line

Pulse Input To Transmission Line

  • With a matched line the load absorbs energy and there is no reflection

  • Open circuit has positive reflections

  • Short Circuit has negative reflections

  • REFLECTION COEFFICIENT(Gamma)

    - Open circuit line > gamma = 1

    - Matched line > gamma = 0

    - Short circuit line > gamma = -1


Gamma and reflection coefficient

Gamma and Reflection Coefficient


Traveling waves along a line

Traveling Waves Along A Line

  • Assume a matched line and a sinusoidal signal source.

  • Traveling wave

  • After initial conditions a steady state situation exists.

  • Signal will appear the same as the source at any point on the line except for time delay.

  • Time delay causes a phase shift ( one period = 360 degrees)


Length of line wavelength phase shift

Length of Line/Wavelength/Phase Shift


Standing waves

Standing Waves

  • Assume a transmission line with an open termination, a reasonably long line and a sinusoidal source

  • After initial reflection the instantaneous values of incident and reflected voltage add algebraically to give a total voltage

  • Resultant amplitude will vary greatly due to constructive and destructive interference between incident and reflected waves


Standing waves contnd

Standing Waves contnd.

  • Reminder: A sine wave applied to a matched line develops an identical sine wave except for phase.

  • If the line is unmatched there will be a reflected wave.

  • The interaction of the two travelling waves (vr and vi) result in a standing wave.

  • SWR = Vmax/Vmin


Sample question

Sample question

  • What length of RG-8/U (vf = .66) would be required to obtain a 30 degree phase shift at 100 Mhz?


  • Login