|
Richard Harrison wrote:
Ian, G3SEK wrote: "Hopefully you will agree that an IDEAL INDUCTANCE does not ever have different currents at its two terminals and does not radiate either." Sorry to disappoint you, but adequate demonstration has already shown different currents in and out of a loading coil. I won`t claim it was an ideal inductor. In that case you have nothing to discuss with me. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Tom Donaly, KA6RUH wrote:
": how do you take the gradient of the current at a point on a transmission line?" Not sure I understand the question. Gradient is the rate of change and that`s the derivative of the current at a given point. Over a certain path it is the difference between the path ends and can be averaged for the path. For convenience, Kraus has collected transmission line formulas. I`m not a typist so I`ll just say they are near the end of the new edition, page 890. In the 1950 edition they can be fornd on pages 506 and 507, also near the end of the book. Work out your own example. Best regards, Richard Harrison, KB5WZI |
Ian
Would you please describe for me the physical arrangement of an IDEAL inductance. I cannot visulise such a thing as I only have seen 'coiled ' inductors ,where each coil has a scientific and analytical relationship to its adjacent coils which thus CREATE an inductance and without which an 'inductance' cannot occur. I don't want to enter the augument that is ensuing on this thread but just want to be sure that there is not an inductance available that is not generated by proximity to other items including its own content (wire length) Using chemical terms, is it an element or a compound if you get my drift , since you later mention that 'inductance.' has a "fundamental physical property................." that does not change regardles of a proximity situation. i.e. Self sufficient.? TIA Art "Ian White, G3SEK" wrote in message ... Cecil Moore wrote: I want you to stop and think a moment, about how an IDEAL INDUCTANCE behaves in an antenna. (Sorry to shout, but every time I type "ideal inductance" quietly, you seem to read something else :-) Ian, please take your own advice. It's pretty obvious that you are thinking about an IDEAL INDUCTANCE in terms of a lumped circuit analysis which is invalid when analyzing a STANDING-WAVE ANTENNA. It makes life easier to compartmentalize your scientific world-view in that way.... but it is deeply, fundamentally wrong. In reality, all true scientific knowledge joins up seamlessly - that's how we *know* it's true! If we can't see how it joins up, that means we still have work to do. Dividing it into compartments that don't join up is lazy and will always lead you false. A fundamental physical property like inductance doesn't change its behaviour depending on the situation it finds itself in. If you cut the antenna wire and insert an ideal, lumped inductance, that inductance will behave in exactly the same way as it does in any other circuit. If you really looked hard at the math of antennas considered as transmission lines, you would find there is no problem whatever about inserting an ideal inductance, with no difference in current between its two terminals. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Tom Donaly wrote:
Cecil Moore wrote: Heh, heh, so you don't believe there is a current drop between the current maximum point and current minimum point on a transmission line with reflections? Seems to me going from 2 amps at a current maximum to 0.1 amps at a current minimum is a measurable drop in total current. Next, Cecil, you're going to be talking about a "current gradient" and a "scalar current field." Here's a question for you, Cecil, and Richard Harrison, and Yuri, too: how do you take the gradient of the current at a point on a transmission line, and, if were possible to do so, what is the physical significance of the result? A total current gradient obviously exists on a transmission line with current minimums and maximums. You can locate those points with a simple pickup loop. The current gradient is caused by the superposition of forward and reflected current waves as described in any transmission line textbook. "Taking the gradient" seems to me to be unnecessary and just a logical diversion away from the qualitative conceptual discussion. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Ian White, G3SEK wrote:
Cecil Moore wrote: Ian, please take your own advice. It's pretty obvious that you are thinking about an IDEAL INDUCTANCE in terms of a lumped circuit analysis which is invalid when analyzing a STANDING-WAVE ANTENNA. It makes life easier to compartmentalize your scientific world-view in that way.... but it is deeply, fundamentally wrong. Would you mind providing some real-world proof of your argument or are you satisfied just to play games in your mind? In reality, all true scientific knowledge joins up seamlessly - that's how we *know* it's true! If we can't see how it joins up, that means we still have work to do. Dividing it into compartments that don't join up is lazy and will always lead you false. Most of our models involve shortcuts. For instance, the shortcut equations for small loops do NOT work for large loops. Your lumped circuit shortcuts don't work for distributed networks. When anything in the circuit is an appreciable percentage of a wavelength, the lumped circuit model doesn't work. That's why the distributed network model was invented. A fundamental physical property like inductance doesn't change its behaviour depending on the situation it finds itself in. If you cut the antenna wire and insert an ideal, lumped inductance, that inductance will behave in exactly the same way as it does in any other circuit. It won't behave at all in reality because an ideal, lumped inductance exists only in the human mind, not in reality. If you want to play mind games, be my guest, but please don't try to pass your mental musings off as reality. The question is not whether your mental current changes through an ideal, lumped inductance existing only in your mind. The question is whether the current changes through a real-world bugcatcher coil that exists in reality. If you really looked hard at the math of antennas considered as transmission lines, you would find there is no problem whatever about inserting an ideal inductance, with no difference in current between its two terminals. An ideal inductance doesn't exist in reality so you are just playing games in your mind. Every real-world coil has a phase shift, i.e. a delay. A phase shift is all that is required for the superposed currents at each end of the coil to be different from each other. You seem to be saying that the phases of the forward and reflected currents don't change through a one-foot diameter, one-foot long bugcatcher coil made from 60 feet of wire? All I can say is, "Get real!" -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Richard Harrison wrote:
Jimmie wrote: "Coiling the wire has nothing to do with how it does or does not radiate,---." Good. Just leave your antenna rolled up. Best regards, Richard Harrison, KB5WZI That's exactly what's done in some "frequency independant" antennas. You can do it with logarithmic spirals or the Archimedean kind, take your pick. 73, Tom Donaly, KA6RUH |
Richard Harrison wrote:
Tom Donaly, KA6RUH wrote: ": how do you take the gradient of the current at a point on a transmission line?" Not sure I understand the question. Gradient is the rate of change and that`s the derivative of the current at a given point. Over a certain path it is the difference between the path ends and can be averaged for the path. For convenience, Kraus has collected transmission line formulas. I`m not a typist so I`ll just say they are near the end of the new edition, page 890. In the 1950 edition they can be fornd on pages 506 and 507, also near the end of the book. Work out your own example. Best regards, Richard Harrison, KB5WZI Thank you, Richard, you just made my point. 73, Tom Donaly, KA6RUH |
wrote:
Ian Would you please describe for me the physical arrangement of an IDEAL inductance. I cannot visulise such a thing as I only have seen 'coiled ' inductors ,where each coil has a scientific and analytical relationship to its adjacent coils which thus CREATE an inductance and without which an 'inductance' cannot occur. I don't want to enter the augument that is ensuing on this thread but just want to be sure that there is not an inductance available that is not generated by proximity to other items including its own content (wire length) Using chemical terms, is it an element or a compound if you get my drift , since you later mention that 'inductance.' has a "fundamental physical property................." that does not change regardles of a proximity situation. i.e. Self sufficient.? TIA Art "Ian White, G3SEK" wrote in message ... Cecil Moore wrote: I want you to stop and think a moment, about how an IDEAL INDUCTANCE behaves in an antenna. (Sorry to shout, but every time I type "ideal inductance" quietly, you seem to read something else :-) Ian, please take your own advice. It's pretty obvious that you are thinking about an IDEAL INDUCTANCE in terms of a lumped circuit analysis which is invalid when analyzing a STANDING-WAVE ANTENNA. It makes life easier to compartmentalize your scientific world-view in that way.... but it is deeply, fundamentally wrong. In reality, all true scientific knowledge joins up seamlessly - that's how we *know* it's true! If we can't see how it joins up, that means we still have work to do. Dividing it into compartments that don't join up is lazy and will always lead you false. A fundamental physical property like inductance doesn't change its behaviour depending on the situation it finds itself in. If you cut the antenna wire and insert an ideal, lumped inductance, that inductance will behave in exactly the same way as it does in any other circuit. If you really looked hard at the math of antennas considered as transmission lines, you would find there is no problem whatever about inserting an ideal inductance, with no difference in current between its two terminals. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek Can you visualize a point mass, Art? An ideal inductance isn't a point mass, but according to the textbooks, one is the mathematical analogue of the other. 73, Tom Donaly, KA6RUH |
Cecil Moore wrote:
Tom Donaly wrote: Cecil Moore wrote: Heh, heh, so you don't believe there is a current drop between the current maximum point and current minimum point on a transmission line with reflections? Seems to me going from 2 amps at a current maximum to 0.1 amps at a current minimum is a measurable drop in total current. Next, Cecil, you're going to be talking about a "current gradient" and a "scalar current field." Here's a question for you, Cecil, and Richard Harrison, and Yuri, too: how do you take the gradient of the current at a point on a transmission line, and, if were possible to do so, what is the physical significance of the result? A total current gradient obviously exists on a transmission line with current minimums and maximums. You can locate those points with a simple pickup loop. The current gradient is caused by the superposition of forward and reflected current waves as described in any transmission line textbook. "Taking the gradient" seems to me to be unnecessary and just a logical diversion away from the qualitative conceptual discussion. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- You and Richard need a refresher course in electromagnetics. I hope Yuri doesn't fall into the same trap. 73, Tom Donaly, KA6RUH |
Cecil Moore wrote:
wrote: Would you please describe for me the physical arrangement of an IDEAL inductance. Art, picture a dimensionless point in your mind. Define that point as an inductance without dimensions, without capacitance, and without resistance. There is your "IDEAL inductance" and exists ONLY in the human mind and certain computer models. Since it is dimensionless, the current into the point and the current out of the point are the same current because they are the same point and, of course, the dimensionless point is traversed instantaneously. Now, without modification, extend that dimensionless concept to a one-foot diameter, one-foot long bugcatcher coil, wound with 60 feet of real-world wire. Assert that the bugcatcher coil has virtually identical characteristics to that previous dimensionless point in your mind. Use a computer model's dimensionless inductor feature to prove your point. That's the present "physical arrangement". :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- There are lots of ways to make inductors, (coils, transmission lines, meander lines, etc.) but there is only one inductance. 73, Tom Donaly, KA6RUH |
"Cecil Moore" wrote in message ... wrote: Would you please describe for me the physical arrangement of an IDEAL inductance. Art, picture a dimensionless point in your mind. Define that point as an inductance without dimensions, without capacitance, and without resistance. I'll stop right there, Dimensionless objects which relies on proximity effects is beyond my ken. To use this as an aproach of dimensional devices with NEC to prove something is like building on sand This is like using complex circuitry and ignoring connection lines that radiate. In mathematics we use a mythical addition of root minus one as a sort of gimmic to solve a problem but we always remove the gimic before the real world answers are given, yet you want to keep the gimmic, ala an imaginary thing which is dimensionless and thus has zero proximity effects even tho proximitry effects is what generates inductance in a dimensionless form. And you want me to use this imaginary dimensionless aproach with NEC which deals with the real world where inductance cannot be dimensionless ? This is where the coil argument started since the field density inside a coil is more than that at any point physically and dimensionaly outside the coil which leads to lumped load errors. I am hoping that Ian will address the question in a more serious way and not as a way to buttress a personal agenda. I suppose I should have made it a seperate posting so it would not be perceived in taking sides e.t.c. Actually I modelled the coil to real world dimensions with a NEC program with copious segments that supplied current levels at multiple points around each turn to get my answers which this thread now suggests that NEC answers could me incorrect thus I am following the thread but not partaking in it. My personal belief is that making EZNEC a part of the debate is a mistake since it contains boundaries that most NEC computor do not have and the coil problem is outside its useable boundaries or imposed limits.If a lumped load is viewed as dimensionless then a computor can be excused as supplying a dimensionless response which can evoke a 'garbage in....' type comment. Like most technical things there is nothing wrong with the use of items such as EZNEC within the limits prescribed by Roy and the coil question is outside the useable limits of the EZNEC program. This response is not meant to be personal to anybody or any program mentioned Art There is your "IDEAL inductance" and exists ONLY in the human mind and certain computer models. Since it is dimensionless, the current into the point and the current out of the point are the same current because they are the same point and, of course, the dimensionless point is traversed instantaneously. Now, without modification, extend that dimensionless concept to a one-foot diameter, one-foot long bugcatcher coil, wound with 60 feet of real-world wire. Assert that the bugcatcher coil has virtually identical characteristics to that previous dimensionless point in your mind. Use a computer model's dimensionless inductor feature to prove your point. That's the present "physical arrangement". :-) -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Tom Donaly wrote:
You and Richard need a refresher course in electromagnetics. I hope Yuri doesn't fall into the same trap. As usual, zero technical content from you. Tom, here's a "circuit" for you. +--------------------------------+ | | source Load | | +--------------------------------+ The source is delivering 200 watts in the form of V=100V and I=2A in phase. The load is 4050 ohms. Using your circuit model, you assert that the current through the source is equal to the current through the load since it is a series circuit. Yet, if the current through the 4050 ohm resistor were actually 2.0A, the power to the load would be about 16,000 watts, thus violating the conservation of energy principle. Is there a current drop from the source to the load? Of course! Does this violate Kirchhoff's laws? Of course not! Why doesn't your circuit model work? Because the wires between the source and the load are 1/4WL of 450 ohm ladder-line thus rendering the circuit model invalid for the application. YOUR CIRCUIT ANALYSIS MODEL DOES *NOT* WORK ON DISTRIBUTED NETWORK PROBLEMS!!! -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Tom Donaly wrote:
There are lots of ways to make inductors, (coils, transmission lines, meander lines, etc.) but there is only one inductance. Have you ever seen the equivalent circuit of a transmission line presented with "only one inductance"? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Wed, 20 Oct 2004 04:49:52 GMT, "
wrote: Actually I modelled the coil to real world dimensions with a NEC program with copious segments that supplied current levels at multiple points around each turn to get my answers which this thread now suggests that NEC answers could me incorrect thus I am following the thread but not partaking in it. Hi Art, Read the thread where it is correctly described and stick with a winner. After all, the difference between the point inductor, and the helical one offers barely half a dB difference in the outcome. No one here could possibly measure that spread accurately (about the quarter of the width of an S-Meter's needle). 73's Richard Clark, KB7QHC |
On Wed, 20 Oct 2004 00:16:49 -0500, Cecil Moore
wrote: Does this violate Kirchhoff's laws? Of course it does, several times. |
Like most technical things there is nothing wrong with the use of items
such as EZNEC within the limits prescribed by Roy and the coil question is outside the useable limits of the EZNEC program. Art, in EZNEC version 4.08 by using HELIX definition menu in WIRES you can define real coil, with segments. I did that at the beginning of this thread using 10m quarter wave loaded antenna showing the difference in the current at the coil ends and also what happens when you move the coil from 1/2 to 3/4 way up from the feed point. That correlates close to modeling of loading inductance by using stub and what was found by measurements in reality. If one insists in modeling loading coil as inductance with zero physical size, then you get W8JI results (same current at the ends) There is a progress, even if some still can't swallow it. 73 Yuri, K3BU.us |
Richard Clark wrote:
Read the thread where it is correctly described and stick with a winner. After all, the difference between the point inductor, and the helical one offers barely half a dB difference in the outcome. The difference in the outcome of the currents is way more than half a dB. It's more like 12 dB. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Richard Clark wrote:
Cecil Moore wrote: Does this violate Kirchhoff's laws? Of course it does, several times. Got news for you, Richard. The current drop from a current loop to a current node is NOT a violation of Kirchhoff's laws. It is a characteristic of distributed networks. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Wed, 20 Oct 2004 09:17:57 -0500, Cecil Moore
wrote: a violation of Kirchhoff's laws. that's right |
Richard Clark wrote:
Cecil Moore wrote: a violation of Kirchhoff's laws. that's right The current in a series loop is NOT constant when the loop is a reasonable percentage of a wavelength and there are reflections present. Please provide proof that violates Kirchhoff's laws. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
On Wed, 20 Oct 2004 09:34:39 -0500, Cecil Moore
wrote: Please provide proof that violates Kirchhoff's laws. Read your own post for proof. |
Tom Donaly wrote:
"You and Richard need a refresher course in electromagnetics." This Richard agrees a refresher course could help. I no longer read the Proceedings of the IRE for fun. It`s been over 50 years since I last darkened the halls of academia. I remember a few things. One hangup I see here is the rule that the current in a series circuit is always the same everywhere. True for circuits small in terms of wavelength. False for unmatched (not terminated in Zo) circuits of a size significant in terms of wavelength. The standing-wave antennas of this thread are less than 1/4 wavelength, but they`re still significant in terms of wavelength with or without loading coils. They are open-circuited and make a big reflection from their open-circuited ends. This reflection causes a current which varies from zero at the open-circuit end to something substantial back a ways from the open-circuit. Between substantial and zero is a current drop. My favorite author. F.E. Terman depicts this current distribution in a dipole (two 1/4-wave antennas back to back) in Fig. 23-2 on page 866 of his 1955 edition. For a whip worked against ground, the current distribution is either half of the dipole representation. Look at Fig.23-2. Anyone can see the current drops to zero at the antenna tips. Loading coils won`t change that. Coils added to bring total antenna inductance to resonance with its capacitance occupy space. Current through a loading coil takes time to traverse the coil. By the time current has made the trip through the coil, current arriving from the source is out of phase to some extent with that arriving through the coil. The delays in transit to both ends of the coil are likely not equal. The inequality in phase results in a difference in volts, amps, and impedance at the two coil ends. Recall, we are discussing r-f, traveling as a wave from both terminals of a generator. It is not d-c emerging from one battery terminal and entering another. Cecil is exactly correct in his characterization of how waves supeerpose to produce standing-wave variations in voltage, current, and impedance in the total series circuit. Proof has been offered by modeling, and measurement. You may accept or reject the observations of others. You could also make your own. Best regards, Richard Harrison, KB5WZI |
Yuri
I was relying on statements from Roy in the past where close spaced wires causes errors. In a inductance coil each wire is in close proximetry to other wires in the coil that undergo voltage changes Thus by his statements his limited number of segments available could cause errors. It was for this reason my modelling picture was the image of a real coil with close spaced coils und unlimited segments available which when increased did not change the supplied.results, the test for finality in modeling. One of the reasons I chose this aproach was when modeling critically coupled coils, lumped loads which are imaginary and dimensionless gave problems with critically coupled distances from the center line of a coil ie inside the coil, to distances to outside the coil in a single plane, as well as the capacitive coupling provided by the length and shape of the coil To me it was important for the program to do it's job with a real life coil without any intrusions and assumptions imposed by the operator. If a program has limitations imposed then it is a sign that human overuling intervention is required to prevent the program from running amuck. But as I stated earlier, I have no intention of getting involved in this thread with its infighting when I respect some people from both camps.and where as previously stated by a poster some responses are posed like a language but are non decipherable Art "Yuri Blanarovich" wrote in message ... Like most technical things there is nothing wrong with the use of items such as EZNEC within the limits prescribed by Roy and the coil question is outside the useable limits of the EZNEC program. Art, in EZNEC version 4.08 by using HELIX definition menu in WIRES you can define real coil, with segments. I did that at the beginning of this thread using 10m quarter wave loaded antenna showing the difference in the current at the coil ends and also what happens when you move the coil from 1/2 to 3/4 way up from the feed point. That correlates close to modeling of loading inductance by using stub and what was found by measurements in reality. If one insists in modeling loading coil as inductance with zero physical size, then you get W8JI results (same current at the ends) There is a progress, even if some still can't swallow it. 73 Yuri, K3BU.us |
Richard Clark wrote:
"Read your own post for proof." An antenna loading coil may have unequal current ingress and egress without violating Kirchoff`s law the same way a speaker matching transformer or pi-network does. The input and output impedances are different, though the power input and output are nearly the same. Best regards, Richard Harrison, KB5WZI |
Tom Donaly wrote:
Next, Cecil, you're going to be talking about a "current gradient" and a "scalar current field." Here's a question for you, Cecil, and Richard Harrison, and Yuri, too: how do you take the gradient of the current at a point on a transmission line, and, if were possible to do so, what is the physical significance of the result? 73, Tom Donaly, KA6RUH The standing wave current profile along, for example, a quarter wave radiator is a cosine function. The gradient then would be the derivative of the cosine function which is a -sine function. 73, ac6xg |
Richard Clark wrote:
Cecil Moore wrote: Please provide proof that violates Kirchhoff's laws. Read your own post for proof. If you think my postings provide proof of a violation of Kirchhoff's laws, you simply do not understand distributed network systems and analysis. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Jim Kelley wrote:
The standing wave current profile along, for example, a quarter wave radiator is a cosine function. The gradient then would be the derivative of the cosine function which is a -sine function. Yep, the feedpoint is at a current loop (max). The open end of the quarter wave radiator is obviously at a current node (min). There are electrically 90 degrees of signal between the current loop and the current node on a standing-wave antenna or on a transmission line with standing waves. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
I was relying on statements from Roy in the past where close spaced wires
causes errors. Roy outlined the limitations as far turns spacing for minimum error, but for the purpose of illustration, the HELIX menu is a big help in modeling or studying the effect of loading coils. In my original example I tried to obey the limitations and wanted to demonstrate that EZNEC can model real life coils and display the current distribution across them. This is especially important when modeling parasitic beams with loaded elements. 73 Yuri |
Cecil Moore wrote:
Tom Donaly wrote: You and Richard need a refresher course in electromagnetics. I hope Yuri doesn't fall into the same trap. As usual, zero technical content from you. Tom, here's a "circuit" for you. +--------------------------------+ | | source Load | | +--------------------------------+ The source is delivering 200 watts in the form of V=100V and I=2A in phase. The load is 4050 ohms. Using your circuit model, you assert that the current through the source is equal to the current through the load since it is a series circuit. Yet, if the current through the 4050 ohm resistor were actually 2.0A, the power to the load would be about 16,000 watts, thus violating the conservation of energy principle. Is there a current drop from the source to the load? Of course! Does this violate Kirchhoff's laws? Of course not! Why doesn't your circuit model work? Because the wires between the source and the load are 1/4WL of 450 ohm ladder-line thus rendering the circuit model invalid for the application. YOUR CIRCUIT ANALYSIS MODEL DOES *NOT* WORK ON DISTRIBUTED NETWORK PROBLEMS!!! -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- You still don't get it, Cecil, which is o.k. since I didn't expect you to. I don't doubt that Yuri can find a coil that exhibits a different current at one end than at the other; I have an antenna that exhibits the same behavior, and I made it that way on purpose. However, the term "current drop" as used by Yuri was wrong. There is no place for it in electromagnetic theory, and if you had known enough theory to understand that, you wouldn't have answered as you did. 73, Tom Donaly, KA6RUH |
Cecil Moore wrote:
Tom Donaly wrote: There are lots of ways to make inductors, (coils, transmission lines, meander lines, etc.) but there is only one inductance. Have you ever seen the equivalent circuit of a transmission line presented with "only one inductance"? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- I don't hook equivalent circuits up to my antennas, Cecil, and I'm surprised that you do. Most of the transmission lines I've ever dealt with had one inductance which the theorists wouldn't think was as important as the inductance per unit length. Besides, you missed the point again. 73, Tom Donaly, KA6RUH |
Richard Clark wrote:
On Wed, 20 Oct 2004 04:49:52 GMT, " wrote: Actually I modelled the coil to real world dimensions with a NEC program with copious segments that supplied current levels at multiple points around each turn to get my answers which this thread now suggests that NEC answers could me incorrect thus I am following the thread but not partaking in it. Hi Art, Read the thread where it is correctly described and stick with a winner. After all, the difference between the point inductor, and the helical one offers barely half a dB difference in the outcome. No one here could possibly measure that spread accurately (about the quarter of the width of an S-Meter's needle). 73's Richard Clark, KB7QHC Hi Richard, you've hit the nail squarely on the head. The validity of the whole argument boils down to whether or not you can safely neglect the effects of the physical dimensions of the inductor on the behavior of the antenna. It looks to me as if you can, but some of the other fellows on this newsgroup seem to be as much interested in characterizing Tom Rauch as a rat as they are in verifying some antenna effects due to the properties of real loading coils. 73, Tom Donaly, KA6RUH |
A good way to check the validity of an EZNEC helix model is to create
the helix by itself, run a wire from one end of the helix to the other right through the middle of the helix, and put a source in the middle of the wire. Specify a low enough frequency that the helix will be small in terms of wavelength. I've found the source reactance to compare quite favorably with the reactance of the inductance calculated by Reg's program for the same physical dimensions. The self resonant frequency comes out quite close, also. The Q should be in the same ballpark, provided wire loss is included in the model, although radiation will lower it some in the EZNEC model. (The source resistance with wire loss set to zero is the radiation resistance. As long as it's much lower than the resistance with wire loss included, the effect of radiation will be small. If it's not much lower, reduce the frequency.) As I mentioned before, EZNEC doesn't model proximity effect (significant only when the turns are pretty closely spaced) but I don't think Reg's program includes proximity effect, either. Roy Lewallen, W7EL |
Richard Harrison wrote:
Tom Donaly wrote: "You and Richard need a refresher course in electromagnetics." This Richard agrees a refresher course could help. I no longer read the Proceedings of the IRE for fun. It`s been over 50 years since I last darkened the halls of academia. I remember a few things. One hangup I see here is the rule that the current in a series circuit is always the same everywhere. True for circuits small in terms of wavelength. False for unmatched (not terminated in Zo) circuits of a size significant in terms of wavelength. The standing-wave antennas of this thread are less than 1/4 wavelength, but they`re still significant in terms of wavelength with or without loading coils. They are open-circuited and make a big reflection from their open-circuited ends. This reflection causes a current which varies from zero at the open-circuit end to something substantial back a ways from the open-circuit. Between substantial and zero is a current drop. My favorite author. F.E. Terman depicts this current distribution in a dipole (two 1/4-wave antennas back to back) in Fig. 23-2 on page 866 of his 1955 edition. For a whip worked against ground, the current distribution is either half of the dipole representation. Look at Fig.23-2. Anyone can see the current drops to zero at the antenna tips. Loading coils won`t change that. Coils added to bring total antenna inductance to resonance with its capacitance occupy space. Current through a loading coil takes time to traverse the coil. By the time current has made the trip through the coil, current arriving from the source is out of phase to some extent with that arriving through the coil. The delays in transit to both ends of the coil are likely not equal. The inequality in phase results in a difference in volts, amps, and impedance at the two coil ends. Recall, we are discussing r-f, traveling as a wave from both terminals of a generator. It is not d-c emerging from one battery terminal and entering another. Cecil is exactly correct in his characterization of how waves supeerpose to produce standing-wave variations in voltage, current, and impedance in the total series circuit. Proof has been offered by modeling, and measurement. You may accept or reject the observations of others. You could also make your own. Best regards, Richard Harrison, KB5WZI Hi Richard, current is the same everywhere in a series circuit only when you can neglect the length of the components. Network theory is supposed to be an abstraction that is close to being accurate only at low frequencies and short dimensions. So, I agree with you. I don't agree with the term "current drop" because, even in a transmission line, current, or more properly, current density, doesn't act like a potential of any sort to which you could ascribe a "drop." You probably think this is nitpicking. I don't think it is, any more than Yuri having a fit over how much the shape of the current is changed in a short, inefficient antenna by a slight change in where the current bends, ie whether it's at the beginning or end of the loading coil. 73, Tom Donaly, KA6RUH |
Jim Kelley wrote:
Tom Donaly wrote: Next, Cecil, you're going to be talking about a "current gradient" and a "scalar current field." Here's a question for you, Cecil, and Richard Harrison, and Yuri, too: how do you take the gradient of the current at a point on a transmission line, and, if were possible to do so, what is the physical significance of the result? 73, Tom Donaly, KA6RUH The standing wave current profile along, for example, a quarter wave radiator is a cosine function. The gradient then would be the derivative of the cosine function which is a -sine function. 73, ac6xg Jim, current, in a wire, is the total current density integrated across a cross section of the wire. It's a vector, as is the current density. Now tell me, how do you take the gradient of a vector? David K. Cheng, in his book Field and Wave Electromagnetics, defines the gradient operation this way: "We define the vector that represents both the magnitude and the direction of the maximum space rate of increase of a scalar as the gradient of that scalar." He wrote "scalar," not "vector," Jim. You and the rest of the boys are acting as if current had magnitude but no direction, whereas it has both. 73, Tom Donaly, KA6RUH |
Cecil Moore wrote:
Jim Kelley wrote: The standing wave current profile along, for example, a quarter wave radiator is a cosine function. The gradient then would be the derivative of the cosine function which is a -sine function. Yep, the feedpoint is at a current loop (max). The open end of the quarter wave radiator is obviously at a current node (min). There are electrically 90 degrees of signal between the current loop and the current node on a standing-wave antenna or on a transmission line with standing waves. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- You're both wrong for reasons I've given in another post. 73, Tom Donaly, KA6RUH |
Tom Donaly wrote: Jim Kelley wrote: Tom Donaly wrote: Next, Cecil, you're going to be talking about a "current gradient" and a "scalar current field." Here's a question for you, Cecil, and Richard Harrison, and Yuri, too: how do you take the gradient of the current at a point on a transmission line, and, if were possible to do so, what is the physical significance of the result? 73, Tom Donaly, KA6RUH The standing wave current profile along, for example, a quarter wave radiator is a cosine function. The gradient then would be the derivative of the cosine function which is a -sine function. 73, ac6xg Jim, current, in a wire, is the total current density integrated across a cross section of the wire. It's a vector, as is the current density. Now tell me, how do you take the gradient of a vector? David K. Cheng, in his book Field and Wave Electromagnetics, defines the gradient operation this way: "We define the vector that represents both the magnitude and the direction of the maximum space rate of increase of a scalar as the gradient of that scalar." He wrote "scalar," not "vector," Jim. You and the rest of the boys are acting as if current had magnitude but no direction, whereas it has both. 73, Tom Donaly, KA6RUH Not sure why you don't like gradients, Tom. I'm sure Mr. Cheng is undoubtedly correct, but I'm just as sure he didn't intend that sentence as any sort of definition of the term "gradient". That's something you have apparently read into it. The gradient in our case (since you proposed the question) would be expressed as the superposition of forward and reverse currents, with magnitude and phase (or direction if you prefer) written as a function of either position or angle *along* the radiator. It's nothing fancy. Honest. It's simply the rate of change of current as a function of position. The gradient across the radiator at any given point along the radiator could then be determined using some additional parameters - if someone were really that interested in it (which I'm not). 73, ac6xg |
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EZNEC doesn't model proximity effect (significant only when the
turns are pretty closely spaced) but I don't think Reg's program includes proximity effect, either. Roy Lewallen, W7EL ====================================== Yes it does! But you can forget it. It doesn't matter except when calculating efficiency. It has no affect on how the thing works which is what you are all so-aggressively fighting about. You'll soon be using assault weapons. Program "Loadcoil" also includes the ALL-IMPORTANT COIL CAPACITANCE (which I suspect Eznec does not - I never use it) - the existence of which the whole set of you block-heads, so-called electrical engineers, appear to be entirely ignorant. We ARE dealing with alternating currents. Oh Boy - I enjoyed typing that! ;o) ---- Reg, G4FGQ |
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