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Current in loading coil, EZNEC - helix
Howdy Antenna NGers,
I took the time to check out the Helix feature in EZNEC 4.08 and modeled the "worst" case - CB whip or 10 m whip with loading coil - helix half way up and then the same helix moved up to 3/4 way up. Things will get more pronounced when more turn, more inductance coil is used and frequencies are lower. Yes, Virginia there is a CURRENT DROP across the loading coil, unless you have more "appropriate" or "scientwific" term for it. Rough dimensions: 1m mast (5 mm copper wire/tubing), 20 cm long coil/helix with 5 cm diameter turns, 5mm wire diameter, 10 turns, spacing 2 cm followed by 1 m whip Resonated at 27.05 MHz With base current 1 A, at the end of mast/start of coil the current is 0.87457 A at the end of coil/start of whip the current is 0.66884 A - a decent drop of 0.20573 A or 20.5 % - not an "EQUAL" (you DC coil believer types!!!) Then I moved the same coil up 50 cm, so the mast was 1.5 m, same coil, followed by .5 m of whip. Again with base current of 1 A, the bottom of the coil had current this time was 0.65479 A, while top of the coil 0.37127 with larger drop of 0.28352 A or 28.3 % - even bigger not "EQUAL" with resonant frequency moving up to 28.7 MHz, which corresponds to REALITY measured, experienced and finally properly (close enough) modeled. Even M0RON (with apologies if there is call like that issued :-) can see the nice current drop across the coil displayed in the VIEW. Thank you Roy (now you believe it?), Cecil, Richard. Now the unbelievers can even model this case themselves and SEE it properly. So ON4UN, K3BU, W9UCW, W5DXP, KB5WZI were and are right. W8JI, G3SEK et al are sooooo wrong :-) Some still persist, some are converted and many will be enlightened. Now if Roy can incorporate elegant way of modeling real life coil/inductance by inputing Inductance L and its physical size and have it calculate things without modeling turns, that would be a winner and a segment saver. So after all, those "dumb" hams pointed out 50 years of misinformation in even ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision" still has it in it) Just watch W8JI to massage his web page and twist out of this one (yet another egg in the face :-) Yuri Blanarovich, www.K3BU.us www.computeradio.us |
Yuri Blanarovich wrote:
Howdy Antenna NGers, I took the time to check out the Helix feature in EZNEC 4.08 and modeled the "worst" case - CB whip or 10 m whip with loading coil - helix half way up and then the same helix moved up to 3/4 way up. Things will get more pronounced when more turn, more inductance coil is used and frequencies are lower. Yes, Virginia there is a CURRENT DROP across the loading coil, unless you have more "appropriate" or "scientwific" term for it. Rough dimensions: 1m mast (5 mm copper wire/tubing), 20 cm long coil/helix with 5 cm diameter turns, 5mm wire diameter, 10 turns, spacing 2 cm followed by 1 m whip Resonated at 27.05 MHz With base current 1 A, at the end of mast/start of coil the current is 0.87457 A at the end of coil/start of whip the current is 0.66884 A - a decent drop of 0.20573 A or 20.5 % - not an "EQUAL" (you DC coil believer types!!!) Then I moved the same coil up 50 cm, so the mast was 1.5 m, same coil, followed by .5 m of whip. Again with base current of 1 A, the bottom of the coil had current this time was 0.65479 A, while top of the coil 0.37127 with larger drop of 0.28352 A or 28.3 % - even bigger not "EQUAL" with resonant frequency moving up to 28.7 MHz, which corresponds to REALITY measured, experienced and finally properly (close enough) modeled. Even M0RON (with apologies if there is call like that issued :-) can see the nice current drop across the coil displayed in the VIEW. Thank you Roy (now you believe it?), Cecil, Richard. Now the unbelievers can even model this case themselves and SEE it properly. So ON4UN, K3BU, W9UCW, W5DXP, KB5WZI were and are right. W8JI, G3SEK et al are sooooo wrong :-) Some still persist, some are converted and many will be enlightened. Now if Roy can incorporate elegant way of modeling real life coil/inductance by inputing Inductance L and its physical size and have it calculate things without modeling turns, that would be a winner and a segment saver. So after all, those "dumb" hams pointed out 50 years of misinformation in even ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision" still has it in it) Just watch W8JI to massage his web page and twist out of this one (yet another egg in the face :-) Yuri Blanarovich, www.K3BU.us www.computeradio.us There may be a difference in current along the coil, but it isn't a current drop. There is no such thing as a current drop in the sense people use when they say "voltage drop." By the way, Yuri, since you are such an unsung genius of electromagnetic analysis, here's a challenge: design a loading coil for a short vertical radiator that doesn't have, or has only very little, current variation along its length. 73, Tom Donaly, KA6RUH |
There may be a difference in current along the coil, but it isn't a current drop. There is no such thing as a current drop in the sense people use when they say "voltage drop." So what you call decrease of current from one to the other? By the way, Yuri, since you are such an unsung genius of electromagnetic analysis, Where is this coming from? here's a challenge: design a loading coil for a short vertical radiator that doesn't have, or has only very little, current variation along its length. 73, Tom Donaly, KA6RUH No need for that, W8JI has plenty of them, go ask him. Are you trying to bu funny or play trolling Chipster here? 73 Yuri |
"Yuri Blanarovich" wrote in message ... Howdy Antenna NGers, (snip) So after all, those "dumb" hams pointed out 50 years of misinformation in even ARRL "bibles" like Antenna and Handbooks :-(yep, latest 2005 "revision" still has it in it) I think you are taking what ARRL says out of context. I will quote from page 16-7 in The ARRL Antenna Book, 20th edition... "The loading coil acts as the lumped constant that it is, and disregarding losses and coil radiation, maintains the same current flow throughout. As a result, the current at the top of a high-Q coil is essentially the same as at the bottom of the coil. This is easily verified by installing RF ammeters immediately above and below the loading coil in a test antenna." Don't overlook the part about disregarding losses and coil radiation. And, don't overlook the part about verifying the current with ammeters. Have you done that? The ARRL book doesn't even recommend using a loading coil with an 8 foot whip on the 10 meter band. Read the whole chapter. Note that your "coil" is 7.4% (6.7 degrees) of the antenna system length. It is no longer the lumped device which is assumed in the book. Please repeat your experiment on an 8-foot whip at 40 meters and then verify with current meters. If you can still make the same assertions for 40 meters, submit your findings to the ARRL for publication. If they find them worthwhile, I'm sure they will publish them. John |
Don't overlook the part about disregarding losses and coil radiation. And,
don't overlook the part about verifying the current with ammeters. Have you done that? The ARRL book doesn't even recommend using a loading coil with an 8 foot whip on the 10 meter band. Read the whole chapter. Note that your "coil" is 7.4% (6.7 degrees) of the antenna system length. It is no longer the lumped device which is assumed in the book. Please repeat your experiment on an 8-foot whip at 40 meters and then verify with current meters. If you can still make the same assertions for 40 meters, submit your findings to the ARRL for publication. If they find them worthwhile, I'm sure they will publish them. John Been there, done it. Check for more story on the subject http://www.k3bu.us/loadingcoils.htm Yuri, K3BU.us |
"Yuri Blanarovich" wrote in message ... Don't overlook the part about disregarding losses and coil radiation. And, don't overlook the part about verifying the current with ammeters. Have you done that? The ARRL book doesn't even recommend using a loading coil with an 8 foot whip on the 10 meter band. Read the whole chapter. Note that your "coil" is 7.4% (6.7 degrees) of the antenna system length. It is no longer the lumped device which is assumed in the book. Please repeat your experiment on an 8-foot whip at 40 meters and then verify with current meters. If you can still make the same assertions for 40 meters, submit your findings to the ARRL for publication. If they find them worthwhile, I'm sure they will publish them. John Been there, done it. Check for more story on the subject http://www.k3bu.us/loadingcoils.htm Yuri, K3BU.us And in which ARRL publication might I find this information? John |
And in which ARRL publication might I find this information? John Since 1953 Belrose article in QST, in all ARRL Antenna Books and Handbooks it is shown that current across the loading coil (mobile or loaded antennas) is uniform, while ON4UN Low Band DXing shows and explains it right. I will have some more samples modeled with EZNEC and one of these days comprehensive article on the subject. Jus' need some free time. Yuri |
"Yuri Blanarovich" wrote in message
... And in which ARRL publication might I find this information? John Since 1953 Belrose article in QST, in all ARRL Antenna Books and Handbooks it is shown that current across the loading coil (mobile or loaded antennas) is uniform, while ON4UN Low Band DXing shows and explains it right. I will have some more samples modeled with EZNEC and one of these days comprehensive article on the subject. Jus' need some free time. Yuri No, I meant in which ARRL publication can I find either ON4UN's or your article correcting the last 50 years of "misinformation?" John |
No, I meant in which ARRL publication can I find either ON4UN's or your article correcting the last 50 years of "misinformation?" John So far the stuff is on my and W5DXP web site, more coming soon as soon as weather and QRL gets more friendly. Stay tuned or do your own measurements. Yuri |
Tom Donaly, KA6RUH wrote:
"There may be a difference in current along the coil, but it isn`t a current drop." Call it a decline if you don`t like the word drop. A wave traveling along an antenna induces current in the wire. This current causes radiation from the wire. A current traveling from "a" to "b" in the wire loses energy to radiation. The energy at "b" is less than the energy at "a" if the source is at "a". If the impedance at "a" is the same as the impedance at "b", the voltage and the current at "a" are larger than the voltage and current at "b". We don`t need energy to decline from "a" to "b" to have a current drop. We only need current to decline between "a" and "b". Yuri has demonstrated a "current drop" with r-f ammeters inserted at both ends of the loading coil. Analysis of the cause is not necessary to demonstrate a current drop. As straight wires are usually better radiators than the same wire in coils, I speculate that the current drop measured by Yuri is mostly due to the high impedance (High voltage, low current) on the output of the loading coil. Best regards, Richard Harrison, KB5WZI |
John Smith wrote:
"And in what ARRL publication might I find this information?" It`s in ON4UN`s "Low-Band DXing", an ARRL publication. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
Tom Donaly, KA6RUH wrote: "There may be a difference in current along the coil, but it isn`t a current drop." Call it a decline if you don`t like the word drop. A wave traveling along an antenna induces current in the wire. This current causes radiation from the wire. A current traveling from "a" to "b" in the wire loses energy to radiation. The energy at "b" is less than the energy at "a" if the source is at "a". If the impedance at "a" is the same as the impedance at "b", the voltage and the current at "a" are larger than the voltage and current at "b". We don`t need energy to decline from "a" to "b" to have a current drop. We only need current to decline between "a" and "b". Yuri has demonstrated a "current drop" with r-f ammeters inserted at both ends of the loading coil. Analysis of the cause is not necessary to demonstrate a current drop. As straight wires are usually better radiators than the same wire in coils, I speculate that the current drop measured by Yuri is mostly due to the high impedance (High voltage, low current) on the output of the loading coil. Best regards, Richard Harrison, KB5WZI I would urge any young person who reads this and wants to understand electromagnetics to get a good book on the subject, read what the authors say, and forget what Richard just posted. He's all wrong. 73, Tom Donaly, KA6RUH |
Tom Donaly, KA6RUH wrote:
"There may be a difference in current along the coil, but it isn`t a current drop." He wrote that about four times, what's the point of it? Smart Alec attitude? If there is something you believe is wrong and you know better, than please correct us stupid hams. Thanks for your patience Richard, KB5WZI, you are one of few decent posters here. 73 Yuri, K3BU |
I would urge any young person who reads this and wants to understand electromagnetics to get a good book on the subject, read what the authors say, and forget what Richard just posted. He's all wrong. 73, Tom Donaly, KA6RUH See what I mean? I urge any young person to read the book about jerks. |
John Smith wrote:
"The loading coil acts as the lumped constant that it is, and disregarding losses and coil radiation, maintains the same current flow throughout. This statement is somewhat misleading. A standing-wave antenna is somewhat like a transmission line with standing waves. There are TWO component currents in a standing wave antenna, forward and reflected. The total current is the phasor sum of those two currents. Even if the forward current were constant and the reflected current were constant, the total current changes because of the phase shift between the forward current phase and reflected current phase as these two phases are changing in opposite directions. For instance, given a 1/4WL ground plane vertical, the forward current and reflected current are in phase at the feedpoint, thus resulting in high current. At the tip top of the 1/4WL ground plane, the reflected current is 180 degrees out of phase with the forward current and their phasor sum is zero at that point. -- 73, Cecil, 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, KA6RUH wrote:
"---forget what Richard just posted." Suits me. You recall the old story about leading a horse to water. Tom rejects measurements of r-f currents at both ends of a loading coil at work. The currents were clearly differing. Tom must be stuck with battereis and the rise and fall these produce in the current of an inductor. A loading coil is usually in the antenna field in our examples. The loading coil is subject to an incident wave and to a reflected wave. These waves combine in a continuously varying phase relation along the coil to make current, impedance, and voltage all functions of their positions along the coil. Every spot along the coil is different when both waves are sensed together. That`s the way SWR works, and we`re discussing standing-wave antennas. I have a 1982 ARRL Antenna Book. On page 13-3 there is a Fig. 6, "Improved Current Distribution Resulting From Center Loading". The loading coil clearly shows less current at its top than at its bottom. Best regards, Richard Harrison, KB5WZI |
Yuri Blanarovich wrote:
I would urge any young person who reads this and wants to understand electromagnetics to get a good book on the subject, read what the authors say, and forget what Richard just posted. He's all wrong. 73, Tom Donaly, KA6RUH See what I mean? I urge any young person to read the book about jerks. The key to understanding the total current in standing-wave antennas is in understanding the forward current and reflected current components and their superposition at different points along the antenna. The cosine distribution of standing-wave current in a 1/2WL dipole is the result of the superposition of forward-traveling current and rearward-traveling reflected current. An unterminated rhombic is a standing-wave antenna because the forward current gets reflected at the open end of the wire. The forward current causes radiation in the forward direction and the reflected current causes radiation in the rearward direction. The radiation "loss" causes the reflected current at the feedpoint to be a lower magnitude than the forward current at the feedpoint. There are standing waves all up and down an unterminated rhombic and the Vtot/Itot feedpoint impedance depends partially upon the phase between the forward current and reflected current and, of course, upon their magnitudes. Properly terminating a rhombic virtually eliminates reflections and turns the antenna into a traveling-wave antenna which radiates mostly in the forward direction. There are virtually no standing waves on such an antenna. These same ideas can be applied to other standing-wave antennas, including a 1/2WL inverted-V. In EZNEC, we can terminate the ends of such an antenna to ground through resistors that eliminate standing waves on the antenna. The feedpoint impedance of such an antenna is in the ballpark of 600 ohms. Where does the low feedpoint impedance of an unterminated 1/2WL inverted-V come from? It comes from the superposition of the forward current and the reflected current at the feedpoint. These two components are in phase and phasor-add to a large current. The two voltage components are 180 deg out of phase and add to a small voltage. small-voltage/large-current is a low feedpoint impedance. Using a minus sign for 180 degrees, the feedpoint impedance of an inverted-V is approximately (Vf-Vr)/(If+Ir). We can understand a standing-wave antenna by doing an analysis of a lossy piece of transmission line. If the losses in the transmission line approximately equal the radiation "loss" of the antenna, the feedpoint impedances will have approximately the same value. Once standing-wave antenna currents are understood, it is easy to see why the total superposed currents at each end of a 75m Bugcatcher coil are nowhere near equal even though the forward current and reflected current at each end of the coil are close to the same value. Circuit analysis works well when there is only one current flowing in a coil. Circuit analysis falls apart when forward and reflected currents are flowing in a coil and distributed network analysis is required when such coils are installed in standing-wave antennas. -- 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 =--- |
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Richard Harrison wrote:
I have a 1982 ARRL Antenna Book. On page 13-3 there is a Fig. 6, "Improved Current Distribution Resulting From Center Loading". The loading coil clearly shows less current at its top than at its bottom. My 1988 version shows the same thing on page 16-4, Fig. 7. Unfortunately, two pages later, in Fig. 10 it shows how the current at the top of a loading coil can be four times higher than would exist in an equal top length of a 90 degree antenna. Since V*I*cos(theta) is the power, does that mean that the voltage at the top of the coil is 1/4 the value of an equal top length of a 90 degree antenna? So the impedance looking into that 15 degrees of whip above the coil is 1/16 of the impedance looking into that same 15 degrees of that same whip mounted above 75 degrees of wire??? Doesn't sound reasonable, does it? Exactly how does that coil manage to change the impedance looking into 15 degrees of whip by a factor of 16 AT THE TOP OF THE COIL????? That's exactly what happens when one uses circuit analysis on a distributed network problem. If circuit analysis worked on such a problem, we wouldn't need distributed network 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 =--- |
Tom Donaly wrote:
Richard Harrison wrote: Tom Donaly, KA6RUH wrote: "There may be a difference in current along the coil, but it isn`t a current drop." Call it a decline if you don`t like the word drop. A wave traveling along an antenna induces current in the wire. This current causes radiation from the wire. A current traveling from "a" to "b" in the wire loses energy to radiation. The energy at "b" is less than the energy at "a" if the source is at "a". If the impedance at "a" is the same as the impedance at "b", the voltage and the current at "a" are larger than the voltage and current at "b". We don`t need energy to decline from "a" to "b" to have a current drop. We only need current to decline between "a" and "b". Yuri has demonstrated a "current drop" with r-f ammeters inserted at both ends of the loading coil. Analysis of the cause is not necessary to demonstrate a current drop. As straight wires are usually better radiators than the same wire in coils, I speculate that the current drop measured by Yuri is mostly due to the high impedance (High voltage, low current) on the output of the loading coil. Best regards, Richard Harrison, KB5WZI I would urge any young person who reads this and wants to understand electromagnetics to get a good book on the subject, read what the authors say, and forget what Richard just posted. He's all wrong. Well, not entirely, if he follows through the logic of what he says. An ideal loading inductance does *not* radiate; therefore the current at its two terminals *must* be the same. I keep coming back to the same point: until someone correctly understands what pure unadulterated inductance does in an antenna, he can never *truly* understand how a real-life loading coil works. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Yuri Blanarovich wrote:
Tom Donaly, KA6RUH wrote: "There may be a difference in current along the coil, but it isn`t a current drop." He wrote that about four times, what's the point of it? Smart Alec attitude? If there is something you believe is wrong and you know better, than please correct us stupid hams. Thanks for your patience Richard, KB5WZI, you are one of few decent posters here. 73 Yuri, K3BU Why should I? You wouldn't believe me anyway since you and Richard are wedded to your own fractured version of electromagnetics. Besides, Tom Rauch does a good enough job on his web page. 73, Tom Donaly, KA6RUH |
Ian White, G3SEK wrote:
"An ideal loading inductance does "not" radiate." A loading coil does not need to radiate to produce significant difference between the current at its ends. The same power may be produced at various impedances. The product of the real voltage and the real current must be the same in all cases for the same power. A loading coil experiences a different voltage to current ratio (impedance) at every point along its length.. This is due to the combination of forward and reflected volts and amps. Because of the reflection, their forward and reflected vectors are rotating in oposite directions. This makes every spot along the paths of these vectors unique with its own voltage to current ratio (impedance). Cecil. W5DXP has already posted in some detail how the forward and reflected values encounter the incident values and their superposition produces a new impedance. That surely happens at the load end of a loading coil. If the phase between the incident and reflected waves, at the coil to whip junction, makes a different impedance than that at the feed end of the coil, it is likely that the coil output current will be different from the coil input current That`s expected. Best regards, Richard Harrison, KB5WZI. |
Why should I? You wouldn't believe me anyway since you and Richard are wedded to your own fractured version of electromagnetics. Besides, Tom Rauch does a good enough job on his web page. 73, Tom Donaly, KA6RUH Thank you, you just 'splained yourself, one of those.... Yuri |
Ian White, G3SEK wrote:
Tom Donaly wrote: Richard Harrison wrote: Tom Donaly, KA6RUH wrote: "There may be a difference in current along the coil, but it isn`t a current drop." Call it a decline if you don`t like the word drop. A wave traveling along an antenna induces current in the wire. This current causes radiation from the wire. A current traveling from "a" to "b" in the wire loses energy to radiation. The energy at "b" is less than the energy at "a" if the source is at "a". If the impedance at "a" is the same as the impedance at "b", the voltage and the current at "a" are larger than the voltage and current at "b". We don`t need energy to decline from "a" to "b" to have a current drop. We only need current to decline between "a" and "b". Yuri has demonstrated a "current drop" with r-f ammeters inserted at both ends of the loading coil. Analysis of the cause is not necessary to demonstrate a current drop. As straight wires are usually better radiators than the same wire in coils, I speculate that the current drop measured by Yuri is mostly due to the high impedance (High voltage, low current) on the output of the loading coil. Best regards, Richard Harrison, KB5WZI I would urge any young person who reads this and wants to understand electromagnetics to get a good book on the subject, read what the authors say, and forget what Richard just posted. He's all wrong. Well, not entirely, if he follows through the logic of what he says. An ideal loading inductance does *not* radiate; therefore the current at its two terminals *must* be the same. I keep coming back to the same point: until someone correctly understands what pure unadulterated inductance does in an antenna, he can never *truly* understand how a real-life loading coil works. You're right about the understanding part Ian, but Yuri is trying to make generalizations based on the measured behavior of real coils without taking too much time to analyze why the behavior of his coils departs from the ideal. Making up terms, such as "current drop" to give more technical credence to his ideas doesn't help. Richard's attempt to justify Yuri's technical jargon is little more than pathetic. 73, Tom Donaly, KA6RUH |
Hi Yuri,
And yet you are on Tom for just such a similar distinction of word choice. Does this illustrate the principles of reciprocity? ;-) 73's Richard Clark, KB7QHC Slight difference. Rauchians choose their words as weapons of smart ass attitude at "morons" who happen to be right, while Rs are wrong. They fail at the discussion of facts and arguments. I resort to (not too proud of it) responding and biting back in order to prove the point. There is reciprocity but not ideal, just like RF current behavior in real coil. And he did it for the fifth time, go figure. Fuggetaboutit! Yuri, K3BU |
Richard Harrison wrote:
Ian White, G3SEK wrote: "An ideal loading inductance does "not" radiate." A loading coil does not need to radiate to produce significant difference between the current at its ends. Those two paragraphs, one right after the other, say it all. You want to gallop straight on to talk about "loading coils". 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 :-) Hopefully you will agree that an IDEAL INDUCTANCE does not ever have different currents at its two terminals, and does not radiate either. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
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Ian White, G3SEK wrote:
An ideal loading inductance does *not* radiate; therefore the current at its two terminals *must* be the same. This is misleading. Since virtually all coil-loaded mobile antennas are *STANDING WAVE* antennas, there are two current components which superpose to your total current. Let's assume a certain loading coil does not radiate. The forward current is the same magnitude at the bottom of the coil and at the top of the coil. The reflected current is the same at the bottom of the coil and at the top of the coil. There is a phase shift through the coil that affects both those currents. The total current is the phasor sum of the forward current and reflected currents. That phasor sum is different at the bottom of the coil and at the top of the coil. The constant current principle definitely applies but there are two component currents with phase shifts to worry about, just as there are in a transmission line with reflections. Do you use circuit analysis on a transmission line with reflections? If not, why do you use circuit analysis on an antenna with reflections? I keep coming back to the same point: until someone correctly understands what pure unadulterated inductance does in an antenna, he can never *truly* understand how a real-life loading coil works. Ian, using circuit analysis on a standing-wave antenna is not valid. Until someone correctly understands that only a distributed network analysis works on a standing-wave antenna, he can never *truly* understand how a real-life loading coil works. Hint: When installed in a standing- wave antenna, a loading coil works like a transmission line so circuit analysis is an invalid approach. The cosine current distribution on a 1/2WL standing-wave antenna is just 180 degrees of a standing current wave which necessarily must possess two superposed current components, forward and reflected. This is just another example of an invalid math model trying to dictate reality instead of reality dictating a valid math model. Until someone understands the nature of forward current and reflected current on standing-wave antennas, one will remain confused and be tempted to use that invalid circuit model. Your circuit model can be used on traveling-wave antennas. It is NOT valid for standing-wave antennas. -- 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:
Besides, Tom Rauch does a good enough job on his web page. Tom Rauch uses a circuit analysis when he should be using a distributed network analysis. That's an easy mistake to make and a hard mistake to admit. -- 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:
Making up terms, such as "current drop" to give more technical credence to his ideas doesn't help. Richard's attempt to justify Yuri's technical jargon is little more than pathetic. There doesn't need to be a current drop through a coil for the total current to be different at each end. Assume a base-loaded mobile system. Assume the forward current through the coil is constant at 1.1 amp. Assume the reflected current through the coil is constant at 1.0 amp. Assume the phase shift through the coil is 45 degrees. If the forward current and reflected current are in phase at the base of the coil (feedpoint) the total current will be 1.1+1.0 = 2.1 amps of total current at the base of the coil. The total current at the top of the coil will be 1.1 amps at -45 degrees superposed with 1.0 amps at +45 degrees. 1.1*cos(-45) + 1.0*cos(45) = 1.48 amps. The coil is lossless and the component currents are absolutely constant through the coil yet the superposed total current at the top of the coil is only about 71% of the superposed total current at the bottom of the coil. No "technical jargon" involved. Using circuit analysis on a distributed network problem simply demonstrates ignorance of the problem. It's an easy mistake to make and a hard mistake to admit. -- 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:
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. The equations governing the behavior of a standing-wave antenna are similar to the equations governing the behavior of a lossy transmission line with reflections. In fact, just by looking at the equations, you cannot tell whether they apply to a transmission line with reflections or to a standing-wave antenna. Hint1: Write the equation for the total current on a standing-wave antenna that includes forward and reflected currents and "loss" due to radiation. Hint2: A real-world mobile loading coil acts like a section of transmission line where Z0=SQRT(L*C). It does NOT act like a lumped circuit inductance. Hint3: An IDEAL INDUCTANCE doesn't exist in reality. Lumped circuit inductances are a shortcut that doesn't exist in reality and surely does NOT apply to distributed networks like a standing-wave antenna. Hopefully you will agree that an IDEAL INDUCTANCE does not ever have different currents at its two terminals, and does not radiate either. Can't agree to that at all. In fact, here's a repeat from another posting that proves that the superposed forward and reflected currents at each end of a lossless inductance *cannot* be equal. Please don't use the copout excuse that an ideal lumped inductance doesn't have any phase shift through it. *ALL* real-world loading coils have a phase shift that can easily be measured. If it has any phase shift at all, the current magnitudes at each end of the coil *cannot* be equal unless a current min/max occurs in the middle of the coil which doesn't happen in a typical mobile antenna. P.S. How about discussing the technical issues instead of the personalities involved? There doesn't need to be a current drop through a coil for the total current to be different at each end. Assume a base-loaded mobile system. Assume the forward current through the coil is constant at 1.1 amp. Assume the reflected current through the coil is constant at 1.0 amp. Assume the phase shift through the coil is 45 degrees. If the forward current and reflected current are in phase at the base of the coil (feedpoint) the total current will be 1.1+1.0 = 2.1 amps of total current at the base of the coil. The total current at the top of the coil will be 1.1 amps at -45 degrees superposed with 1.0 amps at +45 degrees. 1.1*cos(-45) + 1.0*cos(45) = 1.48 amps. The coil is lossless and the component currents are absolutely constant through the coil yet the superposed total current at the top of the coil is only about 71% of the superposed total current at the bottom of the coil. No "technical jargon" involved. Using circuit analysis on a distributed network problem simply demonstrates ignorance of the problem. It's an easy mistake to make and a hard mistake to admit (especially for gurus :-). -- 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:
I will agree in this respect, but not all Toms are Rauchs. The term "Current Drop" is abhorrent to some (a pollution of technical language), an irritant to others, and inconsequential to many who simply enjoy the cat fight. 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. Would you please provide a proof that going from 2 amps to 0.1 amps is NOT a drop in total current? Just one more example of trying to use lumped circuit analysis methods on distributed network problems. Are you guys ever going to learn? Hint: With distributed networks involving an appreciable percentage of a wavelength, there are definitely current drops in the series loop. This certainly applies to 75m Bugcatcher coils used on standing-wave mobile antennas. -- 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, 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. The title: Current in loading coil. EZNEC- helix. This is not about an ideal inductance. An inductor, inductance, or retardation coil is used to provide inductance. An inductor has a second definition: "A passive fluidic element which because of fluid inertness, has a pressure drop that leads flow by essentially 90-degrees." Sounds vaguely familiar. Inductance is defined as a "property of a circuit that tends to oppose any change because of a magnetic field associated with the current itself. Whenever an electric current changes its value, rises or falls, in a circuit, its associated magnetic field changes, and when this links with the conductor itself an emf is induced which tends to oppose the original current change." If the purpose is to provide inductance, and the purpose of thiis inductance is to exhibit Lenz`s law, then an ideal inductor does not radiate, but I`m not convinced it does not have different currents at its two ends, as this says nothing about the coil`s quality or perfection. After all, self inductance is the production of an oppositely directed current in reaction to an imposed current. An ideal coil can very well be arranged not to radiate or couple to the outside world other than through its terminals. These terminals can face very different impedances depending on where each is connected in a circuit with standing waves. That is what confronts the ordinary loading coil in an antenna circuit. Best regards, Richard Harrison, KB5WZI |
Richard Harrison wrote:
An ideal coil can very well be arranged not to radiate or couple to the outside world other than through its terminals. These terminals can face very different impedances depending on where each is connected in a circuit with standing waves. That is what confronts the ordinary loading coil in an antenna circuit. Ever wonder why everyone is ignoring the 180 degree phase-reversing coils described by Kraus in _Antennas_for_all_Applications_? Real- world coils change the phase of the current from end to end. That real-world phase shift is all that is required for the total current at each end of the coil to be different when installed in a standing-wave antenna undergoing superposition of the forward and reflected currents. What we seem to have here is a bunch of gurus who are incapable of admitting that they mistakenly used the lumped circuit model when they should have used the distributed network model. It's an easy mistake to make and a hard mistake to admit. -- 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 =--- |
As straight wires are usually better radiators than the same wire in coils, I speculate that the current drop measured by Yuri is mostly due to the high impedance (High voltage, low current) on the output of the loading coil. What, Coililng the wire has nothing to do with how well it does or does not radiate, only with how the radiation is summed into the total field. The current distribution in a loading coil should be very similar to the current distribution in the secton of antenna it is replacing. |
Jimmie wrote:
What, Coililng the wire has nothing to do with how well it does or does not radiate, only with how the radiation is summed into the total field. The current distribution in a loading coil should be very similar to the current distribution in the secton of antenna it is replacing. Actually, coiling the wire tends to reduce the far-field radiation because much of the near-field(s) cancel each other. The currents on each side of the coil are traveling the opposite direction in much the same way they do in a transmission line. However, that doesn't mean the currents at the bottom and top of the coil are identical. The magnitude of the total current at the bottom and top of the coil depends in large amount on the phase shift through the coil. -- 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 =--- |
Cecil Moore wrote:
Richard Clark wrote: I will agree in this respect, but not all Toms are Rauchs. The term "Current Drop" is abhorrent to some (a pollution of technical language), an irritant to others, and inconsequential to many who simply enjoy the cat fight. 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. Would you please provide a proof that going from 2 amps to 0.1 amps is NOT a drop in total current? Just one more example of trying to use lumped circuit analysis methods on distributed network problems. Are you guys ever going to learn? Hint: With distributed networks involving an appreciable percentage of a wavelength, there are definitely current drops in the series loop. This certainly applies to 75m Bugcatcher coils used on standing-wave mobile antennas. -- 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 =--- 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 |
Cecil, W5DXP wrote:
"Ever wonder why everyone is ignoring the 180 degree phase reversing coil described by Kraus in _Antennas_For_All_Applications_?" TOUCHE`! (They told me "touche`" was more appropriate than "there goes the SOB".) In this thread, the foreign word is sure to offennd somebody. The all-coil phase inverter is another reason to buy Kraus` final book. Best regards, Richard Harrison, KB5WZI |
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 |
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 |
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