Dodge Durango Forum II

Yup! Learned all about EM effect when I went through my electronics classes.

Big Al
al-east@earthlink.net

What happens is a strong enough "moving" magnetic field close enough to the wiring will induce current flow exactly the same way a transformer works (in this case the phone wires are acting like a transformer's secondary windings). While the induced current flow isn't "normally" enough to cause an electrical problem (we're talking milliamps here unless it happens to be the EM associated with a nuke blast - which can easily induce 100s of amps and blow out all kinds of electrical equipment), the problem arises because the "frequencies" also passed across with that current flow can cause all kinds of interference with data transmissions.

Newer computer systems are even more susceptible to this effect because, where the data transmission passes through POTS (Plain Old Telephone System) wiring, it has to be "unloaded" to achieve the higher transmission rates used today! In simple terms that means, "no filters allowed", which "would" take out the interference but would also limit how fast the line can transmit data.

This comes into play because, to achieve those higher transmission rates, the data is encoded using a variable frequency scheme where changing data bits are represented by changing frequencies. The filters normally used for POTS, to give you a good "clean" voice signal while talking, would filter out a large part of those data frequencies because they'd appear to be just line noise. If you've ever had occasion to actually "listened" to a live data transmission you know that's exactly what it sounds like!

Now if you had fiber optics from your computer to the telephone company's DCO (Dial Central Office), you'd never have to worry about such interference. Of course the phone companies aren't in any hurry to replace their old copper wires because they're still making gobs of money using them. Until such time as they can see a higher return for the investment of putting in fiber, it just ain't gonna happen!

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