Part B (continuation)
3. If a transmission line is terminated by a resistance equal to Z then the transmission line behaves at the source end like a resistor with value Z regardless of the length of the transmission line. Such a transmission is said to be "properly terminated".
4. Signals propagate as waves along transmission lines. When the transmission line is properly terminated the waves are absorbed at the load, but if the transmission line is not properly terminated some or all of the wave power is reflected at the load and propagates back to the source. The propagation velocity c for most transmission lines is about two thirds of the speed of light because of the dielectric properties of the plastic insulation material. For a given frequency f, the wavelength l of a signal propagating along a transmission line is l= c/ f.
5. If the transmission line is much shorter than l/4 and is terminated by a resistance much higher than Z, then at the source end the transmission line looks like the terminating resistance paralleled by the transmission line capacitance which is ~100 picofarads per meter.
6. If the transmission line is much shorter than l/4 and is terminated by a resistance much lower than Z, then at the source end the transmission line looks like the terminating resistance in series with the transmission line inductance which is typically of the order of a few hundred nanohenries per meter.
7. If the transmission line length equals l/4, then at the source end a short circuit termination will look like an open circuit while an open circuit termination will look like a short circuit!
8. If the transmission line is longer than l/4 and terminated by an impedance different from Z, then the apparent impedance at the source end will have a strong frequency dependence and there will be resonances at frequencies which are harmonics of a base frequency that is the inverse of the time it takes a wave to propagate from one end of the transmission line to the other. This complicated frequency-dependent behavior will seriously degrade signals.