> > Electricity confuses me. I have two TV sets connected to one cable. They can be tuned to different channels at the same time with no problem. They tell me at the cable company that
> > up to four TV's will work fine even with four different stations.
> >
> > I have four telephones connected to one telephone line. If you talk on one, nobody can use the others.
>
> That's because the TV stations that go through the cable ALL come in at once, at different frequencies, and your TV set just tunes in to one and throws away the others. On the phone line, however, there's only one frequency range you can use, whether it be for a phone call or to put your computer online. Do them at the same time, and you're using the same bandwidth space and garbling each other.
>
> > My new printer has a fax machine and it answers every call after the third ring and won't let me talk on the phone until it assures itself that the call didn't come from another fax.
>
> Would you rather it did? If you answered the phone when it was a fax, your voice and whatever background noise the phone picked up would garble the fax signal, resulting in a...well...INTERESTING looking fax receive.
>
> > My answering machine doesn't answer until the 4th ring, so it won't work unless I unplug the printer.
>
> The woes of cross-manufacturer incompatibility.
> Nothing to be confused about here; the companies that designed the two machines just picked numbers out of a hat, and you happened to get two brand devices that don't seem to work well together.
>
> > I looked at the cable TV coax and it has a single conductor surrounded by a grounded shield. The telephone wire has four insulated conductors.
>
> The coax cable is coax. The telephone cable is copper. There's a VAST difference in the range of frequencies those wires will reliably conduct, and how. It also makes a difference how the wire is used. Your TV cable is intended for one-way communication only. Your phone cable needs to be two way. But the thing about copper is, you can't go two directions at the same time; hence, you need at LEAST two wires, one for sends and one for receives. Coax, interestingly, will reliably conduct signals in both directions on the one wire. Fiber optic cable is expensive, brittle, and hard to repair, but it can conduct a whole heck of a lot of information and doesn't cause electromagnetic interference -- so there are certain circumstances, usually for trunk lines, where that's the best choice.
>
> The capabilities of each wire type all boil down to raw physics, and the choice to use one over the other for particular applications depends on capability, cost, politics, durability, and the availability of the particular technologies at the time of the need for them.

I'll have to think about that for a while to fully understand it. It sounds like you would never need more than two wires, one in each direction, but if you used different frequencies for telephone, computer, fax, etc., you could use them all on the same two wires. But then the phone company would only sell one line per household, and that would hurt their business. I'll bet I wind up with two lines. My youngest son, who is a contractor and operates his business out of his home, has two lines already. Anyway, thanks for the explanation.
Howard