Pulses In Transmission Lines

Purpose

To demonstrate the reflection of pulses in terminated and unterminated transmission lines and to determine the speed of an electromagnetic wave in the transmission line.
 

Equipment

Oscillator, dual trace scope, 100 feet of 50 ohm cable, shorting and 50 ohm terminators.

 

Setup Time

5 min.

Images

k8-32

Description

An oscillator produces pulses at a rate of about 8 Mhz, which are input into the transmission line. The scope is triggered externally and the pulse is displayed on the top trace of the dual trace scope. The pulse at the end of the transmission line is displayed on the bottom trace. For a short section of transmission line the input and output pulses line up. Using 100 feet of transmission line the delay is about 150 ns; for this cable v/c is approximately 0.67 so the wave time is about 1.5 nanosecond per foot.To see reflections, use only the top trace. The far end can be left open, shorted, o
 

References

H. P. Stabler, Apparatus Notes: Pulses on a Transmission Line with a Tektronix 545A Oscilloscope, AJP 29 #2, ix-x (1961). Ronald I. Rank, Speed of a Pulse in a Transmission Line, TPT 7, 344-345 (1969). ◙D. J. Martin, Wave propagation in dispersive and attenuation media: A delay line simulation of plasma waves, AJP 48, 473-477◙(1980). Operating Instructions, Short Wave Radio Demonstration Apparatus, Cenco No. 080435, Cenco Scientific Co., Chicago, IL. Lecture Demonstration Photographs and description of Demonstration.