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Old 10th April 2007, 10:08 PM   #41
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'Best you find a decent physics instructor for this ...

The presence of a current flow in a wire (or shield or screen) does have an effect on any incoming electromagnetic influences (like external EMF noise, internal thermal and internal electrical resistance and capacitance) ... the activity of the radiation of the external source being diminished by this static or dynamic current flow or charge on the wire, thus the total impedence of the wire, end to end is reduced because of the presence of the current flow or charge.

This all takes place at the atomic and sub-atomic level. Because of the dynamic or static "surplus" of electrons (the wire in a charged state), and the resistance to increasing or decreasing current flow in the form of any signal traveling down the wire is improved, mostly because of reduced effective resistance to this changing current flow (any signal). Also effected is the overall capacitance of the wire in relation to the surrounding insulation and and the influence of other local conductors (with a very, very complicated explaination involving static verses dynamic capacitance, influences of any current flow near by in other conductors and the distance thereof, etc.).

Simpler: electrons flow better down a charged wire or shield, resulting improved impedence to the signal.
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Old 10th April 2007, 10:21 PM   #42
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Default sounds like pure BS, I'm afraid!

You made the statement - what are your sources? Where do you get this stuff from? It sounds like the marketing blurb from someone attaching AA cells to his cables.

It is full of inconsistencies "..takes place at the atomic level ..."

EVERYTHING does!

Do you think that signal transmission down cables is a function of electron flow?

Signals in cables can approach the speed of light.

Electron flow is in inches /sec.
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Old 11th April 2007, 12:55 AM   #43
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" ... Do you think that signal transmission down cables is a function of electron flow? Signals in cables can approach the speed of light. Electron flow is in inches /sec. ..."

Yes. Actually under the right conditions, electrons can flow at much faster than inches / sec., more like 60% of the speed of light.

Now, if a conductor is completely devoid of available, surplus electrons (no static charge at all), then it will take considerable time for a small flow of electrons to both electrify the conductor and reach the other end, but that is the point I am trying to make re: the "active" shield or screen ... But if the electrons have then flowed onto and electrified the conductor to a reasonable level, a few volts potential, then the signal, which can be additional electrons or reduced or more deficient state (oscilating between + and - relative), then electron or signals can flow at a much higher speed, in the case of copper wire, as much as 60% of the speed of light.

Sources: http://en.wikipedia.org/wiki/Neutral...legraph_system ... http://en.wikipedia.org/wiki/Quiescent_current ... http://en.wikipedia.org/wiki/DSLAM (Speed and Distance and "... The most common DSLAMs are housed in a telco-grade chassis, which is supplied with (nominal) 48 Volts DC. ..." In part, in order to hold a charge on the signal wires) ... http://en.wikipedia.org/wiki/Ivor_Ca...smission_lines ... http://en.wikipedia.org/wiki/Ivor_Catt#Electron_spin ... etc.
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Old 11th April 2007, 02:37 AM   #44
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Though I usually get pretty good info from Wikipedia, those references are about the worst I've seen. The quiescent current one is meaningless babble. Catt isn't taken seriously by the physics community for good reasons, ones that the many intelligent letters to WW following his articles clearly stated. DC current flow shouldn't affect other signals, in fact, like ripples in a pond, you can have a multitude of unrelated currents passing through a conductor, with no effect on each other. The whole purpose of driven shields is to place zero volts across the dielectric at any instant in time, negating whatever capacitance there is, and eliminating dielectric absorption. That allows one to work at very high impedance with near zero cable losses. We're talking voltage only in the shields, with minimal current flow, since one end is probably left open. Currents flowing in shields are generally a bad thing, since they indicate problems with ground integrity. BTW, it's tough to get near the speed of light with signals- look at cable velocity factor that's published for any serious coax. The speed of electrons is slow, but completely irrelevant to the matter. Not sure what reference to cite, but a good start might be the three volumes of The Feynman Lectures on Physics. Not impossible difficult, but still a reasonably complete foundation, at least the 3% I can grasp
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Old 11th April 2007, 07:28 AM   #45
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Quote:
Originally posted by Conrad Hoffman
The whole purpose of driven shields is to place zero volts across the dielectric at any instant in time, negating whatever capacitance there is, and eliminating dielectric absorption. That allows one to work at very high impedance with near zero cable losses. We're talking voltage only in the shields, with minimal current flow, since one end is probably left open. Currents flowing in shields are generally a bad thing, since they indicate problems with ground integrity.

yeap - the buffer is only feeding the capacitance of the cable....and that current is REALLY small....so we need only to follow voltage at any time (phase following and amplitude following)...
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