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Common and Differential Modalities
wrote in message ... On Sep 3, 3:59 pm, Richard Clark wrote: On Mon, 1 Sep 2008 09:26:26 -0700 (PDT), wrote: In a perfect situation, with a balanced feedline, the only kind of current and voltage you have IS common mode! This statement above contains a serious error of perception while trying to inhabit the debate over BalUns - and it probably corrupts that topic too. First - a circuit has at a minimum two conductors extending from a source. A circuit by its nature is circular: for every charge carrier that enters it, one must exit it. Continuity is a necessary condition for a circuit. No continuity, no conduction, hence an "Open Circuit." Second - those two conductors, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Differential Mode current in anticipation of a common modality. Fourth - if that remote point of connection is replaced with a load, there is a voltage across that load characterized by both the unaltered directions of current, and its now altered magnitude of current. Fifth - this is called Differential Mode voltage in anticipation of a common modality. This completes the discussion of the Differential Mode. If we expand upon this simple model of a source, two wires, and a load and put it into the context of life as we know it; then the circuit operates in the proximity of ground. By convention, ground is called Common. Ground, by convention is an infinite sink of charge of infinite extent. Hence as a conductor, it is available everywhere - Common. This ground may have either deliberate or accidental conductive relationships to the Differential Circuit. First - the linkage of ground to the differential circuit can be through an Ohmic path, or by an inductive path, or by a capacitive path. To support conduction, the circuit must contain two conductive paths to ground through any combination of these linkages, and that path must be complete. The apparent source driving conduction through that path will be a combination of the differential source and the differential load as each will have some relationship to ground. Second - those two conductive paths, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Common Mode current. Fourth - as the differential circuit is original and establishes both the source and the load; then through the introduction of ground, this Common Mode current is mixed with the original Differential Current and analysis must be performed by substitutions to separate them. Fifth - the apparent source presents the Common Mode voltage. This completes the discussion of Common Mode. The applications of a choke to either circuit is commonplace to control each mode's current. It would appear through the context of discussion in other threads that there is some confusion in what is being choked, and how a choke is properly applied is confounded by that confusion. It follows that if the transmission line from the source to load suffers from Common Mode currents, that this must be due to a Common Mode voltage gradient extending from the source to the load. If either lead of that transmission line pair were choked, this would disrupt the Differential Mode. If both leads of the transmission line pair were independently choked, this would only double the disruption. However, if both leads were choked in parallel (both lines either coiled as a pair rather than individually, or both lines penetrate a lossy core) then their fields would be contained between them in the Differential Mode, but their Common Mode path (they both share equal conduction in the same direction due to the Common Mode voltage gradient) will be snubbed. Some BalUns employ these techniques - some don't. BalUns fail by the degree that they don't when Common Mode, as a problem, is injected into the circuit through imbalances. As balance in the proximity of earth and many confounding nearby structures is a forgone failure, choking is a practical necessity for correct BalUn performance. Any issues of BalUn heatings are proof of this choking necessity, and further proof of the demand for additional choking at that point (and frequently elsewhere at wavelength relationships along the affected line). 73's Richard Clark, KB7QHC Let me put it this way (again very simplifed): How do you explain a residential 208V power source where you have 120 V from line 1 and line 2 to ground but 240V with respect to each other. You 240V household appliances operate this way. Ecept for the fact that the lines are 120 degrees out of phase phase (insread of 180 because we use a delta system instead of Y, but this is not that important for this discussion) this is nearly a BALANCED feed, where lines 1 and 2 degrees out of phase at 60 Hz and the voltage of interest is the summation of the two lines. Nearly every home in the USA operates this way. In Europe, 240 V is usually obtained by the voltage difference between line 1 (240V) and earth (0V). That is an unbalanced feed. You can insert a 1:1 isolation transformer using the European system at the input and create the balanced USA system at the output by drawing +120 and -120 at from the output windings assigning imaginary isolated earth at centertap. The isolated ground CANNOT conduct tio real ground if the winding to winding impedance is infinity. Basically, hams' 1:1 baluns do much the same thing: They isolate the real ground as such and prevent currents from flowing down the input ground shield. On this ng in a short space I cannot think of a simpler way to express this although I expect to see many statements (you can't equate 60Hz to RF!). Yes you can; a transformer operates as a transformer in the same wayat any frequency providing you design it properly for the frequency of interest. This subject is not nearly so complicated as some in this group makes it out to be and the topic certainly does not rate articles in amateur publications any more than basic application of ohm's law does. Hi Dfinn I realize that you have asked this question to Richard, who is far better prepared to answer than I am. But, it seems that you are confused about how two sine waves add. Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. All the 208 power lines I am familiar with *are* 208 from terminal to terminal when each leg is 120 "terminal to center". Where did you get the "240"? Jerry KD6JDJ |
Baluns?
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Baluns?
Cecil Moore wrote:
wrote: Nope. The CM choke works precisely because the common mode currents are mirror images, 180 degrees out of phase. You are 100% wrong. From "The IEEE Dictionary": "common-mode (1)(general) The instantaneous algebraic average of two signals applied to a balanced circuit, both signals referred to a common reference." The "instantaneous algebraic average of two signals" 180 degrees out of phase is ZERO. -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Baluns?
Cecil Moore wrote:
wrote: Nope. The CM choke works precisely because the common mode currents are mirror images, 180 degrees out of phase. You are 100% wrong. From "The IEEE Dictionary": "common-mode (1)(general) The instantaneous algebraic average of two signals applied to a balanced circuit, both signals referred to a common reference." The "instantaneous algebraic average of two signals" 180 degrees out of phase is ZERO. Cecil: You must be getting old ... stop man! :-) Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Common and Differential Modalities
"Jerry" wrote in
news:s5Ivk.448$sq3.441@trnddc07: .... I realize that you have asked this question to Richard, who is far better prepared to answer than I am. But, it seems that you are confused about how two sine waves add. Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. All the 208 power lines I am familiar with *are* 208 from terminal to terminal when each leg is 120 "terminal to center". Where did you get the "240"? Jerry KD6JDJ Jerry, in the three wire system with 180° phase difference between Line1 and Line2 wrt Neutral (the centre wire) the voltage Line1 wrt Line2 is exactly twice the Line1 to Neutral voltage. You probably don't use the word Neutral over there, it is the word used for four wire three phase systems and it is equally applicable for a three wire two phase system where the Neutral wire carries the "imbalance" current. None of this is a good analogy to a two wire open transmission line at radio frequencies, principally because the length of conductors at power frequencies is usually a very small part of a wavelength and can be approximated well using a simpler analytical model than the traditional 'Telegrapher's' equations applied to transmission lines. Those who resort to explaining radio frequency transmission lines and transformers using 60Hz models need to justify the accuracy / limits of the approximation. The low frequency model does not explain high frequency roll-off in RF transformers and inductors, so it is clearly incomplete. Almost all of this discussion is using lumped circuit analysis (a low frequency model) to explain not just transmission lines, but conductors with significant mutual coupling (the nominal radiator and its feedline). Owen |
Baluns?
On Sep 3, 10:56*pm, John Smith wrote:
Cecil Moore wrote: wrote: Nope. The CM choke works precisely because the common mode currents are mirror images, 180 degrees out of phase. You are 100% wrong. From "The IEEE Dictionary": "common-mode (1)(general) The instantaneous algebraic average of two signals applied to a balanced circuit, both signals referred to a common reference." The "instantaneous algebraic average of two signals" 180 degrees out of phase is ZERO. Cecil: You must be getting old ... stop man! *:-) Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! Yes, ZERO with respect to the isolated reference point. They are measured with respect to each other, not ground. No current should flow through the ground line if the feed is perfectly balanced. |
Common and Differential Modalities
"Owen Duffy" wrote in message ... "Jerry" wrote in news:s5Ivk.448$sq3.441@trnddc07: ... I realize that you have asked this question to Richard, who is far better prepared to answer than I am. But, it seems that you are confused about how two sine waves add. Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. All the 208 power lines I am familiar with *are* 208 from terminal to terminal when each leg is 120 "terminal to center". Where did you get the "240"? Jerry KD6JDJ Jerry, in the three wire system with 180° phase difference between Line1 and Line2 wrt Neutral (the centre wire) the voltage Line1 wrt Line2 is exactly twice the Line1 to Neutral voltage. You probably don't use the word Neutral over there, it is the word used for four wire three phase systems and it is equally applicable for a three wire two phase system where the Neutral wire carries the "imbalance" current. None of this is a good analogy to a two wire open transmission line at radio frequencies, principally because the length of conductors at power frequencies is usually a very small part of a wavelength and can be approximated well using a simpler analytical model than the traditional 'Telegrapher's' equations applied to transmission lines. Those who resort to explaining radio frequency transmission lines and transformers using 60Hz models need to justify the accuracy / limits of the approximation. The low frequency model does not explain high frequency roll-off in RF transformers and inductors, so it is clearly incomplete. Almost all of this discussion is using lumped circuit analysis (a low frequency model) to explain not just transmission lines, but conductors with significant mutual coupling (the nominal radiator and its feedline). Owen Hi Owen My post to the other guy evidently read as though I was asking a question. Actually I read the original post as to have errors and was expecting some lanswer to justify how 120 degrees can be associated with a set of only 2 terminals. There is *no* 240 volt pair of terminals available in a 208/120 power system. Here in "the states" 208/120 refers to a 3 phase system Y circuit. That means there are 3 sets of single phase 120 volt circuits available at the panel. Also available is a set of three terminals that are 208 volts 3 phase. Jerry |
Common and Differential Modalities
On Sep 3, 11:30*pm, Owen Duffy wrote:
"Jerry" wrote innews:s5Ivk.448$sq3.441@trnddc07: ... * I realize that you have asked this question to Richard, who is far * better prepared to answer than I am. * But, it seems that you are confused about how two sine waves add. *Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. * All the 208 power lines I am familiar with *are* 208 from terminal * to terminal when each leg is 120 "terminal to center". * Where did you get the "240"? * * * * * * * * * * * *Jerry * KD6JDJ Jerry, in the three wire system with 180° phase difference between Line1 and Line2 wrt Neutral (the centre wire) the voltage Line1 wrt Line2 is exactly twice the Line1 to Neutral voltage. You probably don't use the word Neutral over there, it is the word used for four wire three phase systems and it is equally applicable for a three wire two phase system where the Neutral wire carries the "imbalance" current. None of this is a good analogy to a two wire open transmission line at radio frequencies, principally because the length of conductors at power frequencies is usually a very small part of a wavelength and can be approximated well using a simpler analytical model than the traditional 'Telegrapher's' equations applied to transmission lines. Those who resort to explaining radio frequency transmission lines and transformers using 60Hz models need to justify the accuracy / limits of the approximation. The low frequency model does not explain high frequency roll-off in RF transformers and inductors, so it is clearly incomplete. Almost all of this discussion is using lumped circuit analysis (a low frequency model) to explain not just transmission lines, but conductors with significant mutual coupling (the nominal radiator and its feedline). Owen - Hide quoted text - - Show quoted text - I found it difficult to go beyond the simplistic 60 Hz analogy in this discussion to best decribe my concept (when writing on usenet). All one can hope for is that the general idea comes out and hope people realize that the variables you mention do exist as well and do not detract from the very fundamental concepts. |
Baluns?
On Sep 3, 7:12*pm, Cecil Moore wrote:
wrote: Nope. The CM choke works precisely because the common mode currents are mirror images, 180 degrees out of phase. You are 100% wrong. From "The IEEE Dictionary": "common-mode (1)(general) The instantaneous algebraic average of two signals applied to a balanced circuit, both signals referred to a common reference." The "instantaneous algebraic average of two signals" 180 degrees out of phase is ZERO. -- 73, Cecil *http://www.w5dxp.com You reference line 1 to line 2. You put your RF voltmeter acroos the two conductors. When doing so you measure two times the voltage that line 1 or line 2 reads with respect to an imaginary isolated grounbd at the centertap the line 1 or 2 measures separately with respect to centertap. OF COURSE the summation of all points on the common reference is zero at all locations at all times, that is why it is called an isolated "ground"! That is why I said earlier you could connect the centertap of the isolated CM side to real ground with no effect on the circuit in an earlier post. |
Baluns?
On Sep 3, 7:18*pm, Cecil Moore wrote:
wrote: I agree that a balun operating at 14 MHz would be a choke when operating at 70MHz. You would do well to agree that a well-designed W2DU balun operating at 14 MHz is choking the heck out of the 14 MHz common-mode current in order to achieve the balun function. You seem to have the IEEE definitions of differential signals and common-mode signals exactly reversed. Because of that misconception, might you be the one who doesn't understand how baluns work? -- 73, Cecil *http://www.w5dxp.com Cecil, if a transmission line operated in the way you think, it would be radiating fields all along its length transmitting RF all along the length of the line. Nothing would get the antenna. The conductors in the lines MUST carry mirror image currents and voltages to indeed cause the cancellation of fileds you speak about. THAT is how energy gets to the antenna. Ever hear of a ground loop? |
Baluns?
On Sep 3, 10:43*pm, John Smith wrote:
wrote: ... I agree that a balun operating at 14 MHz would be a choke when operating at 70MHz. Oh, gee, then you would also agree that a ferrite core around a power supply lead would begin to act as a reactance when the DC line had an AC component travel its' conductive route--you will be happy to realize most would concur! *ROFLOL Lame ... need I really add more? Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! I am not sure where you are coming from. Are you trying to say that differential mode interference often exists alongside CM interference and diff mode can be filtered by coiling phase wires over a ferrite core? Works for me. I agree. Now, what has that got to do with the discussion? |
Baluns?
On Sep 3, 10:45*pm, John Smith wrote:
wrote: * ... I wouldn't say it was choking the common mode.mode current, I would say it is isolating it from diff mode current by simply creating an isolated ground reference point (you could define it at centertap if you were so inclined). Of course I would agree that the impedance between diff mode current at the input and CM current in the output had better be very high, infinity would be best, *but the finite impedances to load and source respectively should match the balun. If you want to call the ground isolation function "choking", that use of this colloquialism is fine with me but FYI that is not the traditional vernacular for that that application. Also, if the W2DU balun is referred to as the "ugly balun", I do believe the use of a bifilar winding around an air core to create an RF transformer has been around for more than 100 years so I do not understand why it is so-named after a contemporary ham. It is rather simple to go from bifilar enameled copper to using the shield and inner conductor of a coax as "bifilar" conductors. All of this stuff is pretty basic EE (Associate level, not even Bachelors) and I hesitate to spend much more time on it. One thing I can say for sure, you are an idiot ... good luck. What an utter waste of time ... Regards, JS Coming from you that is a compliment. I recommend you stop wasting your time on things you know nothing about. If you agreed with me, then I would have to take another look at what I was saying. |
Baluns?
On Sep 3, 10:47*pm, John Smith wrote:
wrote: ... Because the input and the out windings of the balun must be isolated at least at RF of interest, OF COURSE there should be a high impedance between the ballanced current flow and the unbalanced current flow. However, the impedance of the source looking into the impedance from the souurce should match source impedance and the impedance of the load looking in the output winding of the balun should match the load impedance (say 70 ohms, or 600 ohms or whatever your antenna or trnasmission line impedance is. The impedence at frequency of interest between input winding and output winding should be infinity for isolation purposes (obviously you do not want to mix the unbalanced input and balanced output currents. Hey, are you just a plain idot, or someone who lacks any ability at all to apply logic? *ROFLOL In all my time here, years!, I have never seen as large an idiot as you! * My Gawd, you make the dummies here begin to seem logical! Please plonk me. I don't know how to plonk you using this google web interface...unless you have instructions. I note you do a lot of plonking. And its not due to the heat, it's the senility. |
Common and Differential Modalities
Jerry wrote:
... I realize that you have asked this question to Richard, who is far better prepared to answer than I am. ... Jerry KD6JDJ Huh, didn't know you liked Shakespeare that much. Let me get to the library and dust off the old tomes for you ... Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Common and Differential Modalities
Jerry wrote:
... was expecting some lanswer ... ... Jerry Good, you are expecting it then, an lanswer (lame answer.) Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Common and Differential Modalities
On Sep 3, 10:54*pm, "Jerry" wrote:
wrote in message ... On Sep 3, 3:59 pm, Richard Clark wrote: On Mon, 1 Sep 2008 09:26:26 -0700 (PDT), wrote: In a perfect situation, with a balanced feedline, the only kind of current and voltage you have IS common mode! This statement above contains a serious error of perception while trying to inhabit the debate over BalUns - and it probably corrupts that topic too. First - a circuit has at a minimum two conductors extending from a source. A circuit by its nature is circular: for every charge carrier that enters it, one must exit it. Continuity is a necessary condition for a circuit. No continuity, no conduction, hence an "Open Circuit." Second - those two conductors, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Differential Mode current in anticipation of a common modality. Fourth - if that remote point of connection is replaced with a load, there is a voltage across that load characterized by both the unaltered directions of current, and its now altered magnitude of current. Fifth - this is called Differential Mode voltage in anticipation of a common modality. This completes the discussion of the Differential Mode. If we expand upon this simple model of a source, two wires, and a load and put it into the context of life as we know it; then the circuit operates in the proximity of ground. By convention, ground is called Common. Ground, by convention is an infinite sink of charge of infinite extent. Hence as a conductor, it is available everywhere - Common. This ground may have either deliberate or accidental conductive relationships to the Differential Circuit. First - the linkage of ground to the differential circuit can be through an Ohmic path, or by an inductive path, or by a capacitive path. To support conduction, the circuit must contain two conductive paths to ground through any combination of these linkages, and that path must be complete. The apparent source driving conduction through that path will be a combination of the differential source and the differential load as each will have some relationship to ground. Second - those two conductive paths, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Common Mode current. Fourth - as the differential circuit is original and establishes both the source and the load; then through the introduction of ground, this Common Mode current is mixed with the original Differential Current and analysis must be performed by substitutions to separate them. Fifth - the apparent source presents the Common Mode voltage. This completes the discussion of Common Mode. The applications of a choke to either circuit is commonplace to control each mode's current. It would appear through the context of discussion in other threads that there is some confusion in what is being choked, and how a choke is properly applied is confounded by that confusion. It follows that if the transmission line from the source to load suffers from Common Mode currents, that this must be due to a Common Mode voltage gradient extending from the source to the load. If either lead of that transmission line pair were choked, this would disrupt the Differential Mode. If both leads of the transmission line pair were independently choked, this would only double the disruption. However, if both leads were choked in parallel (both lines either coiled as a pair rather than individually, or both lines penetrate a lossy core) then their fields would be contained between them in the Differential Mode, but their Common Mode path (they both share equal conduction in the same direction due to the Common Mode voltage gradient) will be snubbed. Some BalUns employ these techniques - some don't. BalUns fail by the degree that they don't when Common Mode, as a problem, is injected into the circuit through imbalances. As balance in the proximity of earth and many confounding nearby structures is a forgone failure, choking is a practical necessity for correct BalUn performance. Any issues of BalUn heatings are proof of this choking necessity, and further proof of the demand for additional choking at that point (and frequently elsewhere at wavelength relationships along the affected line). 73's Richard Clark, KB7QHC Let me put it this way (again very simplifed): How do you explain a residential 208V power source where you have 120 V from line 1 and line 2 to ground but 240V with respect to each other. You 240V household appliances operate this way. Ecept for the fact that the lines are 120 degrees out of phase phase (insread of 180 because we use a delta system instead of Y, but this is not that important for this discussion) this is nearly a BALANCED feed, where lines 1 and 2 degrees out of phase at 60 Hz and the voltage of interest is the summation of the two lines. Nearly every home in the USA operates this way. In Europe, 240 V is usually obtained by the voltage difference between line 1 (240V) and earth (0V). That is an unbalanced feed. You can insert a 1:1 isolation transformer using the European system at the input and create the balanced USA system at the output by drawing +120 and -120 at from the output windings assigning imaginary isolated earth at centertap. The isolated ground CANNOT conduct tio real ground if the winding to winding impedance is infinity. Basically, hams' 1:1 baluns do much the same thing: They isolate the real ground as such and prevent currents from flowing down the input ground shield. On this ng in a short space I cannot think of a simpler way to express this although I expect to see many statements (you can't equate 60Hz to RF!). Yes you can; a transformer operates as a transformer in the same wayat any frequency providing you design it properly for the frequency of interest. This subject is not nearly so complicated as some in this group makes it out to be and the topic certainly does not rate articles in amateur publications any more than basic application of ohm's law does. * Hi Dfinn * I realize that you have asked this question to Richard, who is far better prepared to answer than I am. * But, it seems that you are confused about how two sine waves add. *Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. * All the 208 power lines I am familiar with *are* 208 from terminal to terminal when each leg is 120 "terminal to center". * Where did you get the "240"? * * * * * * * * * * * *Jerry * KD6JDJ- Hide quoted text - - Show quoted text - I tried to explain this one failure in my model; it is truely of phase difference of 120 degree, thus you get only 240/SQRT(3) = 208 RMC when measuring from phase 1 relative to phase 2. The cure is to imagine a Y network instead of a delta network; it is much easier to conceptualize but they are not used so much in the US anymore |
Common and Differential Modalities
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Baluns?
On Sep 3, 10:54*pm, John Smith wrote:
wrote: A 1:1 balun IS an RF transformer. Lengths of transmission line wound an air core can function as a 1:1 RF transformer. Does this in any way show you the error you are making? Transformers operate in the same way whether at 60Hz or RF. So much for your "No" statement which seems to demonstrate a certain confidence masked in senility. Actually, NO! A 1:1 balun is a TLT, as stated, properly, by Ownen ... But, what you speak of is frequently an RF Transformer ... how you keep repeating that mistake speaks to your in ability to do research and educate yourself ... it's not the heat it's the senility |
Common and Differential Modalities
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Baluns?
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Baluns?
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Baluns?
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Common and Differential Modalities
Richard Clark wrote:
... 73's Richard Clark, KB7QHC By all means, proceed. However, fair warning, I stopped reading any posts, by you, long ago ... I find that all I can muster is caustic comments from here on out ... Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Baluns?
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Common and Differential Modalities
On Wed, 03 Sep 2008 19:49:55 -0700, John Smith
wrote: My gawd, inappropriately addressed - but accepted nonetheless. an idiot which who takes a hundrend hundred sentences to say write a simple point is little better than an idiot which who cannot even generate write one sentence! Only a little better? Do you have a sentence, or is this another obscure sentiment? 73's Richard Clark, KB7QHC |
Baluns?
"Mike Coslo" wrote in message 36... Do your prayers make any difference, they really don't, because God knew you were going to pray, and he knew his response. You had no choice. You did what you did because God made you do it that way. This of course means that God knows the predestination of every person he created, which means that he knew that he was knowingly condemming a whole lot of people to an eternity of torture. I picked up on these and other inconsistencies in the early 1970s. I've been an atheist ever since. I wish some few atheists weren't such activists about it, though. It gives us bad PR and turns atheism into a religion. |
Common and Differential Modalities
wrote in message ... On Sep 3, 10:54 pm, "Jerry" wrote: wrote in message ... On Sep 3, 3:59 pm, Richard Clark wrote: On Mon, 1 Sep 2008 09:26:26 -0700 (PDT), wrote: In a perfect situation, with a balanced feedline, the only kind of current and voltage you have IS common mode! This statement above contains a serious error of perception while trying to inhabit the debate over BalUns - and it probably corrupts that topic too. First - a circuit has at a minimum two conductors extending from a source. A circuit by its nature is circular: for every charge carrier that enters it, one must exit it. Continuity is a necessary condition for a circuit. No continuity, no conduction, hence an "Open Circuit." Second - those two conductors, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Differential Mode current in anticipation of a common modality. Fourth - if that remote point of connection is replaced with a load, there is a voltage across that load characterized by both the unaltered directions of current, and its now altered magnitude of current. Fifth - this is called Differential Mode voltage in anticipation of a common modality. This completes the discussion of the Differential Mode. If we expand upon this simple model of a source, two wires, and a load and put it into the context of life as we know it; then the circuit operates in the proximity of ground. By convention, ground is called Common. Ground, by convention is an infinite sink of charge of infinite extent. Hence as a conductor, it is available everywhere - Common. This ground may have either deliberate or accidental conductive relationships to the Differential Circuit. First - the linkage of ground to the differential circuit can be through an Ohmic path, or by an inductive path, or by a capacitive path. To support conduction, the circuit must contain two conductive paths to ground through any combination of these linkages, and that path must be complete. The apparent source driving conduction through that path will be a combination of the differential source and the differential load as each will have some relationship to ground. Second - those two conductive paths, if viewed at a remote point where they are joined, have equal and opposite paths of current conduction - to and from that point. This is from Kirchoff's law of currents. Third - this is called Common Mode current. Fourth - as the differential circuit is original and establishes both the source and the load; then through the introduction of ground, this Common Mode current is mixed with the original Differential Current and analysis must be performed by substitutions to separate them. Fifth - the apparent source presents the Common Mode voltage. This completes the discussion of Common Mode. The applications of a choke to either circuit is commonplace to control each mode's current. It would appear through the context of discussion in other threads that there is some confusion in what is being choked, and how a choke is properly applied is confounded by that confusion. It follows that if the transmission line from the source to load suffers from Common Mode currents, that this must be due to a Common Mode voltage gradient extending from the source to the load. If either lead of that transmission line pair were choked, this would disrupt the Differential Mode. If both leads of the transmission line pair were independently choked, this would only double the disruption. However, if both leads were choked in parallel (both lines either coiled as a pair rather than individually, or both lines penetrate a lossy core) then their fields would be contained between them in the Differential Mode, but their Common Mode path (they both share equal conduction in the same direction due to the Common Mode voltage gradient) will be snubbed. Some BalUns employ these techniques - some don't. BalUns fail by the degree that they don't when Common Mode, as a problem, is injected into the circuit through imbalances. As balance in the proximity of earth and many confounding nearby structures is a forgone failure, choking is a practical necessity for correct BalUn performance. Any issues of BalUn heatings are proof of this choking necessity, and further proof of the demand for additional choking at that point (and frequently elsewhere at wavelength relationships along the affected line). 73's Richard Clark, KB7QHC Let me put it this way (again very simplifed): How do you explain a residential 208V power source where you have 120 V from line 1 and line 2 to ground but 240V with respect to each other. You 240V household appliances operate this way. Ecept for the fact that the lines are 120 degrees out of phase phase (insread of 180 because we use a delta system instead of Y, but this is not that important for this discussion) this is nearly a BALANCED feed, where lines 1 and 2 degrees out of phase at 60 Hz and the voltage of interest is the summation of the two lines. Nearly every home in the USA operates this way. In Europe, 240 V is usually obtained by the voltage difference between line 1 (240V) and earth (0V). That is an unbalanced feed. You can insert a 1:1 isolation transformer using the European system at the input and create the balanced USA system at the output by drawing +120 and -120 at from the output windings assigning imaginary isolated earth at centertap. The isolated ground CANNOT conduct tio real ground if the winding to winding impedance is infinity. Basically, hams' 1:1 baluns do much the same thing: They isolate the real ground as such and prevent currents from flowing down the input ground shield. On this ng in a short space I cannot think of a simpler way to express this although I expect to see many statements (you can't equate 60Hz to RF!). Yes you can; a transformer operates as a transformer in the same wayat any frequency providing you design it properly for the frequency of interest. This subject is not nearly so complicated as some in this group makes it out to be and the topic certainly does not rate articles in amateur publications any more than basic application of ohm's law does. Hi Dfinn I realize that you have asked this question to Richard, who is far better prepared to answer than I am. But, it seems that you are confused about how two sine waves add. Maybe I am wrong, and you do know how two sine wave voltages generated at different times and are connected in series combine to being other than 180 degrees from terminal to terminal. All the 208 power lines I am familiar with *are* 208 from terminal to terminal when each leg is 120 "terminal to center". Where did you get the "240"? Jerry KD6JDJ- Hide quoted text - - Show quoted text - I tried to explain this one failure in my model; it is truely of phase difference of 120 degree, thus you get only 240/SQRT(3) = 208 RMC when measuring from phase 1 relative to phase 2. The cure is to imagine a Y network instead of a delta network; it is much easier to conceptualize but they are not used so much in the US anymore Hi Dfinn Where do you measure voltages on any two terminals to get a 120 degree phase reading in a three phase system? How do you divide 240 by the square root of 3 and get 208? Jerry KD6JDJ |
Baluns?
wrote:
Again, you seem to have the IEEE definitions of "differential" and "common-mode" exactly reversed in your head. Really? Do you believe the currents in a resonant 1/2 wave dipole are common mode or differential mode? Assume it is a 1/2WL wire in free space. Where is the common reference? I've heard antenna currents called "common-mode" currents but neither Kraus nor Balanis call those currents "common-mode". They are usually called "antenna currents" (in phase, radiating) vs "transmission line currents" (out of phase, non- radiating). In any case, differential currents on a transmission line are 180 degrees out of phase and ideally, non- radiating. Common-mode currents on a transmission line are in phase and radiate. The currents in a folded dipole are in phase and radiate. Within a ferrite toroid wired in a 1:1 current-choke- balun configuration, common-mode current induces flux in the toroid with virtually none from differential mode. If the device is made out of turns of coax, the differential currents never see the choking impedance. -- 73, Cecil http://www.w5dxp.com |
Baluns?
wrote:
Cecil, if a transmission line operated in the way you think, it would be radiating fields all along its length transmitting RF all along the length of the line. False! This is easy to visualize and prove. Given a 1/2WL folded dipole fed with 300 ohm balanced line: 1. Do the out-of-phase differential transmission line currents radiate? Ideally - NO!, because the fields from the two wires engage in destructive interference and cancel. 2. Do the in-phase antenna currents radiate? YES!, just as they are supposed to do because the fields from the two wires engage in constructive interference and re- enforce each other. Let's look at the balanced output terminals of the current balun at the source. Instantaneous current is flowing out of one terminal while instantaneous current is flowing into the other terminal. I'm sorry, but that is differential, transmission line current. -- 73, Cecil http://www.w5dxp.com |
Baluns?
On Sep 4, 7:51*am, Cecil Moore wrote:
wrote: Again, you seem to have the IEEE definitions of "differential" and "common-mode" exactly reversed in your head. Really? Do you believe the currents in a resonant 1/2 wave dipole are common mode or differential mode? Assume it is a 1/2WL wire in free space. Where is the common reference? There is none unless you choose to define one. You could go halfway down the output choke and call it "common refrerence" or "isolated ground" or whatever you want to call it. Since there usually no need to reference it axcept perhaps for tutorial purposes, I wouldn't call it anything. You could also reference it to earth ground but only if you physically connected it to the aforementioned centertap. I've heard antenna currents called "common-mode" currents but neither Kraus nor Balanis call those currents "common-mode". They are usually called "antenna currents" (in phase, radiating) vs "transmission line currents" (out of phase, non- radiating). In any case, differential currents on a transmission line are 180 degrees out of phase and ideally, non- radiating. Common-mode currents on a transmission line are in phase and radiate. The currents in a folded dipole are in phase and radiate. The ideal transmission line is common mode and does not radiate because the fields cancel as you said earlier. The dipole antenna is ALSO common mode but the fileds do NOT cancel because the conductors are physically 180 degrees apart from each other so they cannot interfere with each other; instead the fields radiate into free space rather than cancel each other out. It is rather simple really. It is correct to call antenna currents "common mode currents". If the currents on a transmission line are differential, how would (COULD) they be converted to common mode currents on the antenna? We would need a 180 degree phase shift somewhere. Answer: the currents on both the transmission line and the antenna are common mode. Within a ferrite toroid wired in a 1:1 current-choke- balun configuration, common-mode current induces flux in the toroid with virtually none from differential mode. If the device is made out of turns of coax, the differential currents never see the choking impedance. Which explains why you should call it a balun and not a choke. If the balun and source impedances match there should be no choking impedance; maximum power trnasfer should occur. -- 73, Cecil *http://www.w5dxp.com |
Baluns?
wrote:
The ideal transmission line is common mode and does not radiate because the fields cancel as you said earlier. The dipole antenna is ALSO common mode but the fileds do NOT cancel because the conductors are physically 180 degrees apart from each other so they cannot interfere with each other; instead the fields radiate into free space rather than cancel each other out. If transmission line currents were common-mode, they would radiate like crazy and would be an antenna instead of a transmission line. When one shorts the two wires together and feeds the system Marconi style against ground, then the currents are common-mode. (Please switch your news-reader to fixed font). A '+' indicates a connection, not polarity. +-------------------- | current reference (V) | Differential currents to antenna +-------------------- Normal Transmission Line mode designed not to radiate +----+------------------ | | current reference (V) | | | Common-mode currents (becomes antenna) | +------------------ GND Marconi Style feed designed to radiate If the currents on a transmission line are differential, how would (COULD) they be converted to common mode currents on the antenna? We would need a 180 degree phase shift somewhere. I'm glad you asked. When we take the last 1/4WL of transmission line and open it up into a dipole, we have rotated one wire by -90 degrees and the other wire by +90 degrees. That's a 180 degree difference. The transmission line currents are 180 degrees out of phase. The extra 180 degrees of physical rotation subtracts from the 180 degrees in the transmission line for a total of zero degrees (in phase) at the antenna feedpoint. This is explained in detail in "Antenna Theory", by Balanis, 2nd edition, page 18. I will try to duplicate it here using fixed font ASCII graphics. In Phase Antenna Currents --------------------+ +-------------------- | | | | +------------------+ | (V) Differential | +--------------------+ Transmission Line Currents Note the out of phase currents in the transmission line results in in-phase currents in the dipole antenna. -- 73, Cecil http://www.w5dxp.com |
Baluns?
Sal M. Onella wrote:
"Mike Coslo" wrote in message 36... Do your prayers make any difference, they really don't, because God knew you were going to pray, and he knew his response. You had no choice. You did what you did because God made you do it that way. This of course means that God knows the predestination of every person he created, which means that he knew that he was knowingly condemming a whole lot of people to an eternity of torture. I picked up on these and other inconsistencies in the early 1970s. I've been an atheist ever since. I wish some few atheists weren't such activists about it, though. It gives us bad PR and turns atheism into a religion. For me, a person is allowed to believe whatever they want, as long as it doesn't affect me. Unfortunately, too many of them don't get that part and want to force themselves on everyone. Oddly enough, the greatest sermon, direct orders from the man himself is ignored by these folk. - 73 de Mike N3LI - |
Baluns?
Mike Coslo wrote:
I was listening to a preacher just last night. According to him, All is preordinated. God knows the outcome of everything and every single thing that has and will ever happen. All is predestinated. This has been known from before he created the unuverse Predestinated?? Does that mean that God knows exactly when you will end your 2-meter mobile QSO, lock up the car and go inside the supermarket for the milk jug the XYL just told you to pick up on the way home? Jim, K7JEB |
Baluns?
Jim, K7JEB wrote:
Mike Coslo wrote: I was listening to a preacher just last night. According to him, All is preordinated. God knows the outcome of everything and every single thing that has and will ever happen. All is predestinated. This has been known from before he created the unuverse Predestinated?? Does that mean that God knows exactly when you will end your 2-meter mobile QSO, lock up the car and go inside the supermarket for the milk jug the XYL just told you to pick up on the way home? You got it. He won't tell you when you lock your keys in the car - even when he already knows you're going to do it! - 73 de Mike N3LI - |
Baluns?
On Fri, 05 Sep 2008 14:19:28 -0400, Michael Coslo
wrote: Jim, K7JEB wrote: Mike Coslo wrote: I was listening to a preacher just last night. According to him, All is preordinated. God knows the outcome of everything and every single thing that has and will ever happen. All is predestinated. This has been known from before he created the unuverse Predestinated?? Does that mean that God knows exactly when you will end your 2-meter mobile QSO, lock up the car and go inside the supermarket for the milk jug the XYL just told you to pick up on the way home? You got it. He won't tell you when you lock your keys in the car - even when he already knows you're going to do it! He won't answer your prayers for the phone number for AAA because he already wrote it on your membership card he knew you left on the dresser. 73's Richard Clark, KB7QHC |
Baluns?
Michael Coslo wrote:
You got it. He won't tell you when you lock your keys in the car - even when he already knows you're going to do it! Even before He told Pharaoh to let His people go, He already knew Pharaoh was predestined to say no. -- 73, Cecil http://www.w5dxp.com |
Baluns?
Richard Clark wrote:
On Fri, 05 Sep 2008 14:19:28 -0400, Michael Coslo wrote: Jim, K7JEB wrote: Mike Coslo wrote: I was listening to a preacher just last night. According to him, All is preordinated. God knows the outcome of everything and every single thing that has and will ever happen. All is predestinated. This has been known from before he created the unuverse Predestinated?? Does that mean that God knows exactly when you will end your 2-meter mobile QSO, lock up the car and go inside the supermarket for the milk jug the XYL just told you to pick up on the way home? You got it. He won't tell you when you lock your keys in the car - even when he already knows you're going to do it! He won't answer your prayers for the phone number for AAA because he already wrote it on your membership card he knew you left on the dresser. If he was a person, he wouldn't be on my Christmas card list. After I wrote that, I realized just how weird the statement was. Oh well, I'll leave it for people's amusement or irritation. Suffice it to say, the XYL wouldn't put up with that sort of behavior.... - 73 de Mike N3LI - |
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