I remember a story, on radio plant in Riga, Lituania, they got a party of receivers that did not work at all. Investigation revealed that a lady in warehouse who worked there many years tried what she believed to correct an error: new capacitors were of different color, she thought it is wrong, so she replaced them by other capacitors from different bin.
She knew nothing about picofarads...
It is high probability that is just an urban legend, or an anecdote simply because during soviet times manufacturing quality/process management was low to non existent, so people used to hyperbolise or make jokes about it.
A bit of OT here. Riga is capital of Latvia. Lithuania's capital is Vilnius.
I don't know why but it is very common mistake.
I remember a story, on radio plant in Riga, Lituania, they got a party of receivers that did not work at all. Investigation revealed that a lady in warehouse who worked there many years tried what she believed to correct an error: new capacitors were of different color, she thought it is wrong, so she replaced them by other capacitors from different bin.
She knew nothing about picofarads...
One engineer who worked for my father was red-green colorblind. Not at all good for resistor color codes.
Later, to help get the right transistors manually inserted, the incoming PNPs got painted on the top of the TO92 case with red nail polish. When I designed something with JFETs (very much unappreciated by production) they got painted white or blue depending on the part.
Would that it were for consumer audio electronics, whose control markings become progressively less legible as our vision deteriorates with age. I think it was Adcom who once experimented with white chassis and dark markings, but evidently it had a low spousal acceptance factor, or lacked appeal in some other way.
Jneutron and JCX thanks for this interesting exchange of thoughts. If you could please explain what is the current centroid and how it is related to loop area, I could learn even more,
Vac
Braun Atelier series, early 1980s.
All-White, from the turntable all the way to the loudspeakers.
(horrible)
Scott
Thank you for the inside look.
If I would ask for your opinion as to why it is not performed on lower freq. Ics too? (Multiple choise question)
a. Negligible effects at these freq.
b. Effects are not that dramatic at these freq.
c. Effects are equally important but layout correction not feasible within IC size, due to large dimentions –length, height- required for lower freq.
d. None of the above. (Please elaborate in 20 words)
JC, KBK, jneutron, bcarso, simon, jcx, thanks for responding.
George
This is probably best setup as a wiki...
The current centroid is the average center of the current. Think of a frisbee balancing on a finger. If you have the (mass) centroid of the frisbee directly above your finger, the frisbee is balanced. If the frisbee is off center, it will tip. If you glue a quarter on the edge, you have changed where the centroid is, and it will have a different balance point which you can find by trial and error.
Now think of the current in a uniform conductive cylindrical wire (with the return path for this current at infinity so there are no proximity effects). At DC, the current will flow equally through the entire cross section of the wire. The current centroid will be exactly in the center of the wire. As you increase the frequency of the current, the current will begin to skin (go to the outside of the wire as a result of the lenz effect (law). The current centroid will remain exactly in the center of the wire.
A braid is exactly this...a cylindrical conductor where the current is confined to the outer "surface" of the wire, in this case the outer surface being the wire. Any current flowing in this braid (again, no proximity) will flow uniformly, and the current centroid is exactly in the geometric center of the braid.
A coax puts a wire in the exact same location as the braid's centroid. For this case, both the central core wire and the braid have centroids which are on the exact same line in space, coaxial... So we say this structure has a common centroid.
If the current is flowing equal and opposite for the core and braid, the magnetic fields external to the structure will cancel. This applies to all structures which have a common centroid.
Loop area is defined as the area which exists between the centroids of the "send" wire and the "return" wire. This loop area is what will trap time varying magnetic flux and as a result, a voltage can be induced between the conductors. A coax has no loop area.
What jcx and I have touched on, is the fact that the loop area can be current dependent. A simple example would be a pc board with a long trace that starts and ends with a source and load rca jack an inch apart on the board, with the "hot" trace on the top surface of the board travelling the entire length and back on the top surface, with the current return via a ground plane. At DC, the "hot" current will flow via the entire top trace from the source jack to the load jack, and the current will return via the shortest resistive path, a straight line jack to jack within the ground plane.
Inductively, this loop has the largest area at DC because the send or hot current goes the entire top trace, and the return current takes a much different path, direct. Because current always takes the path of lowest impedance, at DC the ground return will be resistance dominated. As the frequency increases, the inductance along the straight line starts to come into play, and the path of least reactance within the ground plane starts to migrate towards the top trace. The ground current is attempting to bring it's current centroid as close to the centroid of the hot current. If you measure this system's inductance, you will find it is very high at low frequency, and drops as frequency rises.
In the limit, this setup will act like a stripline, high frequency currents will ignore the entire ground plane and travel directly under the top trace.
With wires and coils and electromagnetics, this effect is referred to as the proximity effect. The biggest problem with coils can be seen in the previous example...at dc, the resistance of the ground plane is very small because it's a honkin conductor. But at high frequency, only a very small portion of the copper is actually conducting, most of it does nothing anymore. In coils, this means that the effective resistance is much higher than the dc resistance of the wire.
This will also occur in a chassis.
The important thing to realize is that as the frequency goes up, the current centroids will attempt to get closer to each other lowering the system inductance. Many physical equipment designs do not worry about this effect. I believe JC et al has been successful because they do not ignore it. Perhaps not fully understand it, but use their ears in liu of maxwells equations in entirety.
My apologies for the length...I'll stop here, it's too long already.
j
ps.. going to have to stop editing for clarity, my 15 minutes is gonna run out.
Last edited:
Gee now I can quote you out of context as saying when you parallel resistors only the lowest value counts!
Very nice piece!
ES
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.
Thanks. It's an interesting exercise to put in 1000 words something that a drawing can easily show..
j
Last edited:
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:
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:
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..
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:
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'.
..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:
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
- Status
- Not open for further replies.