ee's please reply - (or those who think think they may know)

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Art Greenberg wrote:

The klystrons were used as local oscillators for the receiver. In the smaller units, the magnetron was excited by a solid state modulator circuit, but in the larger (25KW and up) commercial marine units I worked on (Decca, Furuno, Kelvin Hughes) the modulators where "valves", aka tubes ;)
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It never occurred to anybody that a semiconductor device could replace a vacuum tube for any purpose other than as a rectifier until Shockley came up with the idea in the mid-1940s of the transistor, and he couldn't have done that without a great deal of research into the nature of semiconductors, which research was the result of a need in radar development for low-inductance components.
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Tom Watson wrote:

This is, in fact, done in some cases. I recall one 50KW broadcast transmitter wherein a colleague of mine had to replace the tuning coils. Instead of paying a small fortune to the manufacturer for what he needed, he made his own out of ordinary copper water pipe - exactly because the very high currents involved were carried on the surface of the coil "winding" anyway. Note that this is not even particularly high frequency stuff, the AM broadcast band running from about 500-1500 Khz.
Interestingly, he had to do this because the station had purchased a used transmitter (50KW broadcast transmitters are NOT cheap) but it was tuned to the wrong frequency. He reengineered it himself by changing the aforementioned coil and a few other parts and got the thing to sit right on the frequency they needed. As I understand it, they passed FCC proof-of-performance handily.
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On Fri, 15 Jun 2007 20:33:23 -0500, Tim Daneliuk

And this is exactly the reason why smaller coils and cavities are often silver plated copper. the whole thing doesnt need to be silver, just the skin.
dickm
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than gold but electricity as well.
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Tom Watson wrote: | There have been a number of responses so far, many of which | reference the "skin effect" - why the hell do we continue to | produce wire that has a core of the same conductive capacity as the | surface, at great cost, when we might manufacture a wire of a | cheaper core material, with the surface conductor at optimum.?
It's already been/being done. Check out wire for electrified fences at your local farm store. Mild steel core with copper exterior. I used it for building VHF transmit/receive antennas.
One more thing: VHF antennas work better when (a) wire diameter is increased and (b) the wire is polished mirror bright.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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wrote:

I remember building 40M antennas out of Copperweld wire. A steel core with a copper skin. You had to be careful with that stuff. Cut the ties holding the coil of wire together and, BOING, like letting go of a spring, you were immediately standing in the middle of a tangled mess of wire that you didnt dare kink. It would take hours to untangle.
dickm
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dicko wrote:
| I remember building 40M antennas out of Copperweld wire. A steel | core with a copper skin. You had to be careful with that stuff. | Cut the ties holding the coil of wire together and, BOING, like | letting go of a spring, you were immediately standing in the middle | of a tangled mess of wire that you didnt dare kink. It would take | hours to untangle.
SOP was to tie one end around a tree and the other end around a car bumper (remember when we could do that?) and let the car creep foreward until the tightness could be either heard (twunggg) or felt.
When the wire was snipped (next to the knots) it would stay as straight as you please. :-)
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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At 60 Hz, the skin depth is inches (and wire a fraction of an inch across is the norm). At higher frequencies, you see silver-plated wire and most CATV cable is copper-plated iron for the central wire. So, common wire products DO use less conductive materials in the core.
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In high frequency situations we don't Tom. Conductors for such things as radio towers are often hollow core conductors.
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Tom first off.... I've seen them plate aluminum wire with copper and copper cores plated with carbon. Cost not performance the factor... Secondly as much BS as there is electrons flow the path of least resistence but basically it's the whole hose principle..... Current is the controlling factor. Put a 20g wire under 20A and watch it fail.
Copper will easily be cheaper then "gold" plating the wire. and essentually you'll find plenty of it (gold plated) where humidity and environment is a factor to oxidation and corrosion more so then low current loads like Scada data leads or Hi-Def Audio circuitry.

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At DC the entire volume of the conductor is carrying current, not just the surface. The DC resistance of a conductor is: R = [bulk resistivity] x [length] / [cross sectional area] In the above area is independent of geometry. It works for round, square, triangular, etc. If current only flowed on the surface the above equation would have the wire circumference in it instead of area.
For AC skin depth is a factor as others have already pointed out. Changing the geometry of the conductor, from a rod to a sheet, is one remedy for this. Litz wire is another and it is good for up to about 1MHz IIRC.
Art

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wrote:

Experimenting with light weight conductors is always being done. But the holy grail is room temp super conductor. The skin effect does happen but at the diameter of the conductors generally used it is not a problem (DC current). The electrons are forced in a random pattern similar to the way photons travel within the suns deepest layers changing from atom to atom within the conductor, but with a very limited area.
But as Davis Estep once told me in my beginning of my tech career, either it is forward biased or not.
It works or it does not.
Not an EE, but a eclectic electronic technician of over 25 years.
Mark (sixoneeight) = 618
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[snipped for brevity]

Please add some more information:
1) define 'thick' ('thickness' can be manipulated via the increase in voltage carried.... jack up the voltage high enough, and I can push a whack of power through a wire the size of a human hair.) 2) at what frequency, or range of frequencies?
r
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IIRC in 6th grade science class I learned that the energy travels on the outside of the wire.

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wrote:

This is _very_ well understood. If an "EE" doesn't understand this, I can only assume they've spent their life working on 60Hz kit and never gone near a radio.
Electrons go everywhere. At low frequencies, a substantial number are in the middle of the conductor, and that might be a thick conductor.
If you consider a high frequency though, there's an exponential (i.e. gradual) fall off with depth. This leads to "skin effect" and is why VHF radios used to use Litz wire (many strands, so much more "surface to diameter" ratio) and why VHF / UHF uses silver plating on the surface of conductors. Above UHF, it's mostly waveguides rather than conductors.
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Hello Tom, You're post has brought out some erudition on the subject of electical engineeering. If this keeps up I suspect our NG will be discussing entropy and a deeper understanding of gravity, with respect to woodworking of course. Joe G
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Tom Watson wrote:

Wow, small things can occupy small minds. I know fer shure this's the first place I'd ask a fisics kwestion!
Pop`
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I've had a bit of time to refine my understanding of the real world problem that engendered this inquiry.
We are trying to run a carrier in a trough that is 1/2" wide by 3/4" deep. This carrier will feed five LED arrays that are composed of 54 Watts each.
The maximum length of the run is 100 feet.
I was worried that the wire would have to be of such a size that it would not fit, and, more importantly, the connectors would not fit, in the available volume.
It seems to be the case that I need not have worried.
BTW - my apologies for the apparent disparagement of engineers in my post. I was actually responding to one person, but tarred the profession with the same brush.
I have the greatest respect for engineers and deal with them on a more or less daily basis.
That one guy pissed me off and I shot back at him. My apologies to those who were caught in the crossfire.
Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1/On Fri, 15 Jun 2007 19:43:14 -0400,

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Tom Watson wrote:

S'OK Tom - we engineers are not only rather creative - we're a forgiving lot :)
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