2025-12-10
Transmission Line Construction
The transmission lines in these experiments are made from commonly available small diameter magnet wire spaced apart with plastic straw insulators. By selecting AWG number or spacing, a large range of TEM impedances can be produced. Graph 1 shows the calculated TEM impedance for balanced open-wire lines made for several different wire gauges using the standing equation
\(Z_0=276\cosh ^{-1}(\frac s d)\) where s is conductor diameter, d is spacing between conductors
commonly used in textbooks and handbooks, as previously described.
Figure : Calculated 2-Wire balanced line impedances assuming TEM propagation for several different AWG wire sizes. A 754 ohm line is also shown as a limit for twice the impedance of free space if lines are considered independent and each 377 ohm TM.
Many of the experiments use spacers made from plastic straws and 3D printed end-plug fasteners to help maintain desired spacing along a span.
Figure : 3D printable plastic plugs secure line conductors in position at each end of a short piece of plastic drinking straw. A small amount of glue is not required but can be used to make this permanent.