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Old 5th June 2012, 01:50 PM   #23671
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Quote:
Originally Posted by simon7000 View Post
Gee now I can quote you out of context as saying when you parallel resistors only the lowest value counts!
I'm going to have to hurt you...

What is inherently interesting in your comment is the concept of lowest value. In the case of proximity effect, the impedance of the paths is dependent on the current in the path as well as the return currents near the path. If for example, you parallel five 1 ohm resistors side by side, and put the return conductor next to one, the resistance will be frequency dependent. At dc, it will be 200 milliohms. As frequency goes up, the resistance will begin to climb to a value of 1. Eventually, even that resistor will start to proximity as well as skin.

edit: it must also be noted that because the 5 resistors were planar by construction, each resistor will see a different magnetic field caused by the currents within. Even with the return conductor far away, the center and edge resistors will behave differently at frequency. A truly good resistor composite would be all 5 arranged in a symmetrical fashion along the edge of a circle, and the return current going down the exact center (common centroid) of the composite (or via a braid external to the entire resistor construct). That will give the most frequency independent resistor possible using five resistors.
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Very nice piece!

ES
Thanks. It's an interesting exercise to put in 1000 words something that a drawing can easily show..

j

Last edited by jneutron; 5th June 2012 at 02:11 PM.
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Old 5th June 2012, 01:57 PM   #23672
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On of my pet bugaboos is verities such as "Electricity always takes the path of least resistance."

Which just ain't so. You just came close as you know the difference between impedance and resistance, but I did feel the need to point the issue out.
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Old 5th June 2012, 02:02 PM   #23673
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Originally Posted by simon7000 View Post
On of my pet bugaboos is verities such as "Electricity always takes the path of least resistance."

Which just ain't so. You just came close as you know the difference between impedance and resistance, but I did feel the need to point the issue out.
We share that bugaboo. In actuality, the current density profile is entirely dependent on the reactance of the path.

For the purposes of this dialogue, it is the concept of frequency dependent path that is important, specifically the entities responsible for that frequency dependence. Actual computational analysis of the current distribution using the analytic equations is not something for the weak of heart. Having an understanding of the physics helps a lot, and design/test/evaluation is key...test being a combination of test equipment and ears..and evaluation being the noggin.

j

ps..the "path of least resistance", while not entirely accurate, is an important concept for the layman. It helps people avoid electrocution or being hit by lightning, without having to teach them maxwell's equations first.. While we can bristle at the inaccuracy, it serves a very useful purpose..

Last edited by jneutron; 5th June 2012 at 02:15 PM.
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Old 5th June 2012, 02:26 PM   #23674
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Originally Posted by gpapag View Post
(Please elaborate in 20 words)
George
pfft. Clearly, that leaves me out..

j
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Old 5th June 2012, 02:36 PM   #23675
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Huh?? that was tongue in cheek...nothing true about it at all..



That on the other hand, is an accurate depiction of rf and solid copper busswork. And it wasn't oxide in threading...rf doesn't penetrate to the bolts, it's all surface.

They were changing the geometry of the conductors to alter impedance and prop velocity, that's all.

Same thing happens in solid state microwave hybrids. Since the small signal parameters of the semi's can only be close, the traces many times require tuning, either stubs or actual blobs of silver epoxy planted on the traces in historically useable locations. That technique was unfortunately, an "art", as it was not possible to apply a smith chart to the problem.

j
micro dc and associated issues can provide a mushy bit of a 'bed', with respect to the complex LCR of that micro elevated DC (or unwanted AC parameters), and this skews the loading and propagation of the given RF. That's All I was saying, regarding the Oxide issue.

I may state it differently, and we get into clarity and communications error..but I think (hope) you get my communication, here.

Issues of bad grounding cause subtle re-routing of RF (bleed, etc),that is running and propagating where design did not place it. So, due to aging, etc,this must be addressed as part of the potential set of issues in the given tuning attempt. Thus a good whack on the bus bar, for that alone, if not the other reason(s). That's my feeble understanding, one might say, having never dealt directly with such issues. I tend to stay away from RF, but have looked at it, as one has to -if they do audio.

Last edited by KBK; 5th June 2012 at 02:54 PM.
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Old 5th June 2012, 02:52 PM   #23676
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Originally Posted by KBK View Post
I may state it differently, and we get into clarity and communications error.
What you've stated has no meaning to me.

I understand the rf, I understand the em theory, I understand tuning, I understand current distribution.

Your verbage, I do not understand..

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.but I think (hope) you get my communication, here.
No. Sorry.

RF bleed appears somewhat close to the concept of an enclosure starting to broadcast externally, for example, when a cover plate gasket has lost ground continuity... removing the plate, cleaning the gasketed surfaces, then replacing it and re-torquing the holding screws is a common enough fix to a bleed problem.. Sometimes, people mistakenly believe they actually did something internally, when all they did was clean the gaskets..

j

Last edited by jneutron; 5th June 2012 at 02:56 PM.
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Old 5th June 2012, 03:06 PM   #23677
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I tend to see it as...

..regarding Maxwell, It is not specifically the math that counts.

The observation and the understanding came before and outweigh the mathematical descriptors. The math may allow other things to be seen or understood but cannot stand in place for personal observation and logic applied to analysis.

A core point that not many consider: the place in the human mind that the thought patterns erupt from, those that become words within the mind as expression of thought, is considerably more intelligent than the words formed. this is a natural state that has to and does exist, once one considers for a few minutes. the abstract into the concrete logic formation, that deeper parameter is smarter than, more intelligent than the words. Obvious. Therefore, the text can never outweigh logic and intuitive thought, as it flows into expression of thought and logic. The communicative aspect is the failure point. But is is all we have, so we use it, this clumsy tool.

The old 'the map is not the territory' problem, for some. which indicates that it is, for the larger part, categorically insane to use books of prior data to center all descriptors in searching for answers in all unknowns, or to project all prior/extant text... as solution for all unknowns.

It is a good place to start (OOO), but ultimately, the logic of the base parameter behind the text itself says to the literate: To understand that knowledge flows and changes and the book will not be permanent or be the full understanding, ever.

Engineers... are specifically taught that it is in permanence. For they execute along lines of logic that are like that of a policeman. They enforce the 'law', they build within known parameters.

Theoretical and exploratory sciences... say that it is going to be an overturn. It is a matter of eventuality. (or addendum that change the perspective/view/conditionals strongly)

Within the issue of complex unknowns, the matter of eventuality is what can loom. The notion of logic and observation... is to correctly make those distinctions.

And as they say: 'good luck with that'.

Last edited by KBK; 5th June 2012 at 03:16 PM.
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Old 5th June 2012, 03:10 PM   #23678
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Old 5th June 2012, 03:13 PM   #23679
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Originally Posted by KBK View Post
I tend to see it as...

..regarding Maxwell, It is not specifically the math that counts.
Which is all fine and dandy. As I've stated, the absolute accuracy of a tenet is sometimes not as important as the message it conveys.

Unfortunately, putting phrases such as "micro dc", "micro elevated dc", "loading and propogation" into a sentence does not make it a coherent thought. It is indeed, a sentence structure more resembling that of an explosion in a thesaurus factory for engineers.

The concept of tuning by hammer, and bleed caused by cover gasket grounding issues are indeed valid, but they are independent concepts. Lumping them together is also a non-sequitor..

j
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Old 5th June 2012, 03:22 PM   #23680
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Originally Posted by jneutron View Post

j

ps..the "path of least resistance", while not entirely accurate, is an important concept for the layman. It helps people avoid electrocution or being hit by lightning, without having to teach them maxwell's equations first.. While we can bristle at the inaccuracy, it serves a very useful purpose..
Darwin had a better explanation and you don't even need to know it to participate!
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