Visualizing standing waves along the two parallel conducting pipes using household electronic appliances

Abstract

This paper describes an experiment to visualize the voltage standing wave pattern along two parallel terminated conducting pipes using a home VCR and TV modulator as a transmitter, a small dipole antenna as a detector, and a computer with a TV card as a receiver. Students can observe the periodic variation of red color intensity on a PC monitor or TV screen while the dipole antenna scans the RF modulated video signals along the two parallel conducting pipes. The measurement of relative voltage (electric field) intensity is carried out by computing the red color component of a captured video image using simple R, G, B channel analysis. The resultant voltage standing waves achieved in open-circuited termination experiments at various applied UHF channels are discussed in terms of incoming waves, reflecting waves, and conducting loss of the transmission line. The measured wavelengths and computed phase velocities of the standing waves are plotted as a function of UHF carrier frequencies. A short-circuit terminated experiment is conducted and compared with an open-circuited case. The interleaving standing wave patterns of the two contrasting data sets in the short- and open-circuited termination experiment results demonstrate the boundary conditions predicted by field theory.