The power factor case is "semantically" different than the SWR case in the following way: With SWR, energy is flowing in both directions at near the speed of light. If the reflected signal is the exact same frequency as the forward signal (as in the case where it is a reflection of a signal at a particular frequency, then there will be points along the line where the forward and reflects will be in phase and point along the line where they will be out of phase. SWR is a ratio of the max voltage to the min voltage. If there is no reflection, there is nothing to add or subtract, and so the max and min voltage will be the same. The ratio (SWR) is therefore 1:1. If all energy is reflected, the minimum will be zero, so that ratio of the max to the min will be infinite.
Now if I simultaneously measure a power line at 10 different point in a mile, I would detect no significant difference in power factor between the points. This is because the voltage anywhere on the wire is the same (san some IR drop), and the current into one end in the same as the current flowing out the other end. Therefore, the angle between the voltage and current waveforms wil be the same all aong the run. ...Well, not exactly: 60 Hz has a period of 16.7ms. On quarter wavelength is roughly where transmission line effects become significant. One quarter of a period is at 60Hz is 4.17ms. If c=2.98x10^8 meters per second, it would travel 1241.7km in a quarter cycle. (Actually, it is slightly less due to the relative delectric constant of air being slightly higher than that of a vacuum.) If the distance between the source and the load is significantly less than this, no significant steady-state effects will be observable. (Transient effects such as spikes could be seen if a power line broke in a windstorm.) If I were to measure our power line at points much further apart (say thoudands of miles) we could indeed measure a difference because what happens is sufficiently delayed with respect the other points. Thus the adjective "semantically". When we talk about power factor the tacit assumption is that the same voltage exists at all locatons of the wires and that the current in equals the current out (i.e. that we are talking about distances much much smaller than a quarter wavelength). When we talk about SWR (or more correctly VSWR) we tacitly assume we are talking about transmission lines of the order of or longer than a quarter wavelength. Jeff Condit
