Very interesting theory. I am teaching SWR at present to my third year college students. Could be a good discussion point since they have already studied power factor. However, SWR can exist with a purely resistive mismatched load, so it needs a bit of modification to take all into account.
73 Nigel ve3id --- In Repeater-Builder@yahoogroups.com, "Bob Witte K0NR" <[EMAIL PROTECTED]> wrote: > > --- In Repeater-Builder@yahoogroups.com, "kb9bpf" <kb9bpf@> wrote: > > > > Since I'm way more into RF than industrial power distribution, I've > > always been able to think of "power factor" on the electrical power > > grid in terms similar to antenna system reflections, which are > > commonly measured in terms of SWR. After all, both are AC systems > > where the voltage and current bear a phase relationship to each > > other. > > > > When they are perfectly in phase the power factor is 1.0, and a 60-Hz > > SWR meter would measure 1:1. When they are out of phase (power factor > > <1) that SWR meter would read greater than 1:1. I suspect, though I > > haven't done the math or looked up the specific matahematical > > definition of power factor, that it would be direcly proportional to > > the reciprocal of the power factor. And as we know, when that happens > > the power generating end has more difficulty delivering power > > efficiently to the load. > > > > A while back I was doing some analysis of power factor to understand > it better and I found that it has a lot in common with SWR. Both are > focused on the issue of power transfer, so I guess we shouldn't be > surprised. The thing they really have in common is for max power with > AC signals, the voltage and current need to be in phase (phase angle > of zero). > > For linear systems with nice sine waves, PF = cos (phase angle) > where phase angle = the angle between voltage and current sinusoids > > Wikipedia has a good explanation of PF at > http://en.wikipedia.org/wiki/Power_factor > > Play around with some typical circuits and you'll find that an SWR of > 1 also has voltage and current in phase. Again, not a surprise since > it represents the best power transfer. > > This is from memory, so the usual disclaimers apply :-) > > 73, Bob K0NR >
