Lab 3. Pulse Propagation and Dispersion

NAME                                

Introduction.

In this experiment you will observe reflection and transmission of incident pulses as they propagate down a coaxial transmission line. Please review Secs. 5.1 through 5.4 of RWVD (SES Sec. 1.7).

You will observe the effects of matched and mismatched termination impedances on the amplitude and sign of the reflected pulses. By measuring the time between the arrival of the incident and reflected pulses, you will calculate the length of the line. By varying the pulse width you will observe the superposition of the incident and reflected pulses.

Control Settings:

Procedure:

1. Carefully measure the time delay between the incident and reflected pulses and use this information to calculate the length of the line. Note that and for the insulating material between inner and outer conductors. Thus the velocity of the pulses is less than the velocity of light (  m/sec).

   Approximate length of line:        m.

   Is your measured length reasonable?        .

2. Using the control settings as a guide, display the incident and reflected pulses on the scope. Terminate the line with the various terminations provided. Below note the type of termination used and carefully draw the incident and reflected (if any) pulses. In the space below this, briefly relate your observations to what you have learned in lecture.

Termination: Short

The reflection coefficient is -1 for this case. Why is the amplitude of the reflected pulse smaller than the amplitude of the applied pulse? 

What is the measured roundtrip attenuation ?

        .

Termination: 50 

Comments: 

Termination: 10 

Measured reflection coefficient:         .

Theoretical reflection coefficient for lossless line:         .

        .

Comments: 

Termination: 100 

Measured reflection coefficient:         .

Theoretical reflection coefficient for lossless line:         .

        .

Comments: 

Termination: Open

With an open termination on the line vary the width of the incident pulse and observe the effect of this change on the waveform displayed on the scope. Draw the waveform below and explain briefly what has happened.

Let a transmission line having characteristic impedance [ ], attenuation constant and length l [m] be terminated in a load resistor [ ].

Let [V] be the amplitude (magnitude) of the incident pulse at the generator, and [V] be the amplitude (magnitude) of the reflected pulse at the generator. The reflection coefficent at the load is . Therefore, the measured reflection coefficient magnitude at the generator is:

From your measurements of for an open circuited load, use the above equation to calculate the attenuation constant          .