Electromagnetic Waves

Project

Time-domain pulse reflections


Overview

Work in assigned project groups. 

The objective of this project is to simulate and measure time-domain pulse reflections.

NOTE: Use the Project Report Template

IN NO CASE may code or files be exchanged between students, and each student must answer the questions themselves and do their own plots, NO COPYING of any sort! Nevertheless, students are encouraged to collaborate in the lab session.



Part 1: Measurements

  • Pulse reflection measurements:
  • Organize the pulse reflection experiment as shown below

  • Spring 2019 setup using equipment in open lab area:
  • zz
    Fig 001a
    zz
    Fig 001b
    zz
    Fig001c
     
  • Connect a 10-dB attenuator to the input of both scope channels as shown above (to create 50 ohm input impedance at the scope).
  • Also make sure the scope probes are set to 1:1 as shown above. 
  • Set Channel 1voltage scale to 500 mV/div, set Channel 2 at 500 mV/div, and time to 50 ns/div as shown above
  • Connect the cables as shown with the 25 foot long cable connected between the tee on the pulse generator and the tee on the channel 2 input of the oscilloscope as shown.  A shorter cable connects the pulse generator tee to the channel 1 input of the scope. 
  • As shown above, at channel 2 of the oscilloscope, two tees are used to add a pair of 50 ohm terminations in parallel with the channel 2 input 10 dB attenuator.  These three 50-ohm impedances effectively terminate the cable in 16.7 ohms when the two terminations are combined in parallel with the 50 ohm attenuator impedance.
  • Similarly the 50 ohm impedance of the attenuator at scope channel 1 along with the 50 ohm impedance of the signal source, result in a net Thevenin source impedance of 25 ohms driving the long cable. 
  • Set the pulse generator for  pulse waveform, 1 MHz frequency, 40 ns pulsewidth, 8.4ns rise/fall time as shown above.
  • adjust the signal generator amplitude  so you have a 2 V peak pulse when the signal generator is connected to channel 1 of the oscilloscope, including the two 10 dB attenuators, and all other terminations/connectors/cables/etc. above   Also, adjust the offset voltage of the signal generator so that the baseline of your waveform is at zero volts.
  • Set the oscilloscope display as above, and the pulses should appear fairly similar to Fig 001b above
  • Save the plot on a thumb drive for your report, especially noting the peak voltages of the first 2 pulses on each channel


  • Detach the two 50-ohm terminations from the tee on channel2, and obsrve the reflections on the two wavefoms.
  • what happened to the reflections and why?
  • Save the plot without reflections for your report
  • What is the measured velocity of the pulses in the line, expressed as a fraction of the speed of light, such as 0.4c? 
  • The oscilloscope traces should be nearly the same as your simulation below!

  • Part 2: Simulation

    Start the software:

  • From a Linux terminal, ADS should be available in the  menu (Applications::ElecEngineering::KeysightAdvancedDesignSystem)
  • From a PC terminal, you must first open a remote Linux session, then proceed as for a Linux terminal
  • For snapshots use the Linux menu Applications::Graphic::Ksnapshot and select the option to take a legible snapshot of a window rather than a full screen snapshot.
  • Note: (the following note may not be valid after 2009) 
  • If you find that you have printing problem, see if you have a file ".XprinterDefaults" in your home directory. Move this file to ".XprinterDefaultsOld", and restart ADS ... it will write a new copy of this file that should enable printing.
    if this does not work, move your current ".XprinterDefaults" file to ".XprinterDefaultsOld", and try downloading .XprinterDefaults to your home directory. (To download you may need to hold down the "shift key" while you click on the link.) Select the LPDEST printer by File-->PrintSetup-->Options and select Default Printer ($LPDEST) on default_queue
  • FIRST: create a folder/directory in your home directory named apps and a subfolder in apps named ads
  • After ADS starts you should get a starting window similar to this (navigate into your apps/ads folder):


  • Click the help menu item in the upper right (MenuBar::Help) and read through the on-line manuals (see the help tab in ADS), for particular questions it is usually best to use the help index from the ADS window MenuBar::Help to search the manuals.
  • Note: there might be a bug with the main help items, in that you may need to have a web browser such as fireffox open before help will appear in the browser window .
  • Load and run the pulse example as follows:
  • Download the 7zap archive as follows:
  • x

  • You should find a new directory RFcourse2012_pulse1a_wrk created in apps/ads

  • Run ADS and open the new RFcourse2012_pulse1a_wrk workbook by double-clicking it

  • Go down through the directory tree to pulse1/schematic and double click that schematic file, and the following schematic should appear.  (1 mil = 1/1000 inch)


  • Double-click the transmission line and look at the variables in the pop-up menu. 
  • Use the mouse to select the variables and observe the changing description at the bottom of the pop-up.
  • Double-click the "gear" icon (shown below) in the upper right of the window to simulate.

    z

  • The data plotting window should appear.
  • Click the "rectangular plot" icon (shown below) in the left of the new popup window to get a plotting grid by dropping the plotting box in the visible area.

    z

  • In the pop-up window:

    Select DataSet -> V1 -> Add
    Select DataSet -> V2 -> Add
    Select DataSet -> Vsrc -> Add

  • Click OK at the bottom of the popup
  • Drop a second plotting box in the visible area, and in the pop-up window:
  • Select DataSet -> V1 -> Add
  • Click OK, and the following Time-domain plot should appear.

  • Save your schematics and plots before exiting ADS


  • xx
    Fig 003

  • Save a snapshot of your new schematic and paste it into your report.
  • (SEE BELOW FOR THE REPORT TEMPLATE)
  • Make sure that your plots, component values, legends, axes, and fonts are legible in your report!

  • Run the simulation and plot the voltages at the input and output  of the transmission line, and add 4 markers to show the pulse voltages of the first two pulses at the input and output of the transmission line as shown below:
  • xx
    Fig 004

  • Save a snapshot of your input/output pulses as shown above, with markers added,  and paste it into your report.
  • Compute Gamma 1 from the component values on the schematic (reflection coefficient at 1st reflection, at interface between source and transmission line)
  • Does the simulated voltage agree with your computed reflection coefficient?
  • Compute Gamma 2 from the component values on the schematic (reflection coefficient at the reflection at far end of line, at the load)
  • Compute Gamma 3 from the component values on the schematic (reflection coefficient at input, after "round-trip" return)
  • At the input of the line, for the first pulse reflection, what is the reflection coefficient Gamma1? 
  • At the input of the line, for the first pulse reflection, what is the incident pulse voltage, reflected pulse voltage, and total voltage? 
  • At the output of the line, for the first output, what is the reflection coefficient Gamma2? 
  • At the output of the line, for the first pulse output, what is the incident pulse voltage, reflected pulse voltage, and total voltage?

  • Save your schematics and plots before exiting ADS


    Report Data


    NOTE ReportTemplate: Use the Project Report Template 

      YOU MUST ADD CAPTIONS AND FIGURE NUMBERS TO ALL FIGURES!! 

    Copyright 2010-2019 T. Weldon

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