I'm pretty sure that cost still dictates magnetron transmitters in recreational (marine) and virtually all commercial radars. I spot-checked a few Furuno and Raymarine units between 4KW and 60KW, and they use magnetrons. I wasn't able to find any on-line references to klystron based units. I also wasn't able to find any on-line product brochures or other evidence of commercially available all solid-state radars, which surprises me greatly.
Back when I was a little closer to this, in the early 90s, there was work being done to put together all solid-state radar transmitters. But the transistors of that era were unable to do make very high peak power pulses needed for high resolution returns. There was discussion of using signal processing techniques in both the transmitter and receiver to compensate for longer pulse durations. But at the time, that kind of processing was costly. It certainly should be much more in reach today.
I was able to find a few items on-line that talk about military solid-state radar dating to as early as 1992, and a report about an FAA test of a solid-state ASR in 1994.
| 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. :-)
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 ;)
Just bear in mind that lightning is an electroSTATIC phenomenon not electroMAGNETIC one. It's been way to many years since I actually had to know anything about this stuff, but IIRC, the behaviors of electrostatics are governed by rather different mathematics than electromagnetics (which are described by Maxwell's Equations). So ... what you see at the museum is not exactly the same thing under discussion here. It's still fun to watch though :)
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.
the '60s and Gerard K. O'Neill designed a system that would transmit power from orbit in gigawatt quantities.
Using it for cell phones and the like, one might be able to have a local charger in one's car or on one's desk that charges the phone without having to plug it in, but having all cell phones charged from a central power transmitter is unlikely in the extreme.
Tom's trying to oversimplify a complicated question and then produce an engineering design based on that oversimplified analysis.
Electrons in a conductor flow wherever the electromagnetic field in the conductor causes them to flow. At DC levels the field is more or less uniform throughout the conductor so they'll move more or less uniformly through the entire cross section. At AC levels where skin effect becomes an issue the electrons will flow more heavily near the surface than at the center, with the details depending on the geometry, the frequency, and the current.
The trouble with his notion of using "thin coatings" is that there still has to be enough cross sectional area to carry the current. At 60 Hz AC levels, trying to use a "thin coating" for household wiring doesn't gain you anything--the diameter of a solid conductior is much less than the skin thickness and making the conductor a shell wouldn't reduce the amount of conductive material needed, it would just make the conductor more costly to manufacture and more difficult to handle. In substations at very high currents the diameter of the conductor becomes large relative to the skin thickness and it becomes beneficial to use his "thin coating" in the form of tubular busbars. This is also done in the aforementioned aluminum clad steel transmission lines, however in that case the hollow center is in effect filled with the steel structural element.
As for his electrical engineer friend, EEs don't generally deal with electrons unless they're designing vacuum tubes, they deal with fields--for the distribution of electrons in a conductor he'd really have to ask a solid state physicist.
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.
I marked the thread with an OT because I'm trying to be helpful and Tom apparently forgot to do it.
But, as regards the reasoning, I have to agree with Tom. For many years there were some really, really bright people working on heavier than air flight Da Vinci, for one) ... and a couple of bicycle mechanics from Ohio share the honors with a Latin American bon-vivant for solving the basic problems.
While Goddard gets much of the credit for space flight, a lot of very intelligent Chinese had solved most of the problem centuries earlier ... but never finished up.
It's hard to point at any single area of life and say 'IF there was an answer THESE people would know what it is.' I can say it ... but it's hard to keep a straight face.
I do rather suspect that enough research would reveal that the question has already been considered since one of the areas engineers are often found considering is price.
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
tjwats>I had a conversation with a friend of mine today who has a masters in
I've never seen busbars much thicker than that, even in DC systems.
I used to work in telephone exchanges, back in the days of Strowger etc. _Lots_ of power was needed to run an exchange, all distributed at 50V DC. The bus bars were copper strip, about 1/2" from memory and up to 12" wide. Generally the thickness was standard everywhere, but the width was proportional to the current for that citcuit. For a really big feed, such as the one from the battery room downstairs, these busbars would be paralleled up and spaced slightly apart. Mainly this was done for ease of mechanically forming busbars, as two 1/2" strips are easier to install than one 1" strip. It also meant thought that skin effect wouldn't have been a problem, even at 50Hz.
It isn't. You might generate lightning by a static phenomenon, but if a current flows (ie there's a flash) then it will also generate the magnetic effects.
There's also the question of Tesla coils, which are AC anyway. Most of the museum "lightning demonstrations" you see are done with Teslas, rather than an electrostatc machine. Except in Boston though, where they still have that huge Van de Graaff generator that's sometimes used for "geek in a cage" shows.
Wading in very late on this discussion, but the answer to virtually every question of the general form "why don't they do ..." is very simple. "Money".
And, in the specific instance you raise, Tom, the answer is "In the situations where it makes economic sense to do so, they *do*, and have, for _many_ years."
One of the more common examples is 'hollow tubes' used at RF frequencies. One can't get much cheaper than air for a 'core material'. It's amazing how much RF energy at even AM radio frequencies that, say
1/2" copper water tubing can carry.
Most high-power microwave waveguides -- which are nothing more than a thin layer metal surrounding an air core -- *are* _GOLD_ plated. Have been, for
*decades*. For exactly the reasons you the designers of _not_ considering.
'Solid' conductors made of dissimilar materials introduce a raft of other engineering issues. Differing 'coefficient of expansion' in the materials can introduce _major_ stresses, contributing to *GREATLY* reduced life-span. If you reduce the 'cost' by 20%, but the life-span is reduced by 50% you _are_ at a net loss.
In addition, 'bi-metallic' conductors are *MUCH* more expensive to manufacture than ones of monolithic construction. There is a lot more to building wire than just the 'cost of materials'.
And, the fact remains, that at 'power line' frequencies, the 'skin effect' is minimal, except on _very_ large cables.
The _killer_ is that "very large" cables are a _bad_choice_ *economically*. One can move the same amount of energy over a *smaller* cable, by simply using a higher voltage. Which is more efficient for other reasons as well.
In short, the question you raise is a "solved problem". The physics haven't changed in the last 50 years, although manufacturing techniques have. And folks like the E.P.I. _do_ keep an eye on developments in the manufacturing arts. If a 'solution' comes along that is _cheaper_ than present methodologies, they *WILL* jump on it.
Example: substations and switchyards use a lot of rigid hollow-tube 'wiring'. For *short* runs, where you don't have 'parabolic sag' issues, it is more effective than conventional wire. Over longer spans, however, conventional 'solid core' wire strands "win", because of the 'adaptability' and consequent less frequent need for support structures.
Summary: Your 'bright idea' is *well-known* in the industry, and has been used for many _decades_ in contexts where it makes economic sense to do so. You don't see much about it, because it is such _common_practice_ in the areas where it is economically viable that nobody bothers to talk about it -- it *is* just the way 'everybody does it'.
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