Lyle:
Don't have much timme but:
(1) If you take "standard" wave equations using very complex math, then, set the frequencies at or near zero, most of the complicated stuff falls out. I recall doing so in an exercise in one of my "RF type" classes in school.
If I understand you correctly, you are assserting that every conductor is a waveguide, and I agree. Again, at very low frequencies ("low" and "high" here are relative; "low" could mean less than a gHz, while "high" could mean more than, etc. It's all in the point of view, at least in this context); at low frequencies, so many terms in the complex wave equations become so small that almost no error accrues if one simply crosses them out. In the exercise I mentioned above, I began with wave equations and, at "DC frequencies", wound up with Ohm's Law. (For example, what is the period of a DC signal? If T=1/f, and f=0, as in DC, then, using "plain math", it is "undefined". Using limits, T->infinity, and so forth).
If I did not state that the current produces the fields, I apologize, since it is the flow of current in any circuit which produces "work"; voltage is a potential and cannot "flow", etc. Any other errors in semantics, etc., I apologize for. Just don't have a lot of time to write whole books here any more, nor to proofread as carefully as I should. I depend upon working practitioners such as you to point out the details and keep it all straight, eh?
I have also heard of the systems which use existing power lines IN THE HOME as a home network. This is feasible; in fact, I have helped to design some systems like this, which distribute POTS signals, TV signals, data signals, etc. One sticky problem is that the home is ususally powered by a 220v to 110v transformer, where the 110v is obtained by a split 220v secondary. Approximately 1/2 of the 110v circuits in the house are wired to one half of the secondary, and the reamining 1/2 to the other half of the secondary. The tough part for the home distribution is "jumping" a signal from one of the secondaries to the other without special wiring (if one is allowed to attach special stuff to the transformer or perhaps the incoming lines, well, who knows? FCC regs would not allow that in the past but perhaps that has changed now....)
This is also often "botched"; for example, in a home I once owned, if certain lights burned out, other lights would come on at half brilliance; once, a ground fault caused the 220v electric stove to malfunction in an entertaining manner: when the oven was turned on, the lights in the mud room and one upstairs bathroom would turn on at low brilliance! In another home, when I attempted to connect the basement (which I had correctly wired to code and had inspected to verify this) to the existing wiring, I got about a 0.1 megaton fusion phenomenon for perhaps a millisecond, until enough copper vaporized to stop it. Still don't know quite how the electricians who did the upstairs managed THAT one.
But I digress. The thing is, there are some companies who seem to be seriously claiming to be able to send data over long distances, including the last mile, via standard power distribution nets. And they are claiming VERY high data rates; they seem to have demonstrated, in limited trials (where have I heard about THOSE before!), that they can send hundreds of mbytes, and they claim gbytes are posible. I guess we will just have to wait and see.
Anyone can claim anything, as we all know.
Nice to hear from you again.
Larry
you said:
"There are existing schemes where narrowband signals can be broadcast around one's home on the
power lines. There were(are?)music set-ups where a speaker is plugged into the wall and plays
music from the base system. Don't know exactly how they operate"
They use modulated RF carrier, then demodulate at the speaker. Some work quite well but there is ALWAYS some degradation when the transmitter is on one half of the 220v secondary and the receiver(s) on the other; sometimes complex compensation can overcome this well enough, though. |
