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Baluns?
Owen Duffy wrote:
... I suggest that a reasonable definition of a balun is any device that facilitates or assists transition from unbalanced to balanced mode of operation. That definition permits a wide range of devices that may have characteristics suited to specific applications. ... Owen Baluns and Ununs use a transmission line mode to accomplish their tasks .... anything else is just a RF xfrmr ... However, there are the 180 degree hybrid baluns ... Regards, JS |
Baluns?
John Smith wrote:
However, this URL: http://www.n0ss.net/qrp_4-1_guanella-type_balun.pdf in the include pick 4-1_schematic.jpg, in the URL, contains a "blurb" on how to move a single core design on to two cores. Did you mean a two core design onto one core? Here is an analysis of the single core version: http://www.vk1od.net/balun/gsc/index.htm . Guanella did not show the 4:1 balun on a shared magnetic circuit, and it is an error on the part of those who think that the two independent TLTs in Guanella's circuit can be coupled without changing the behaviour significantly (basically, ruining it). Owen |
Baluns?
Here is a URL for design/implementation of "non-standard"
baluns/transformers, but of a highly useable and desirable nature--or, Dr. Sevick strikes again!: http://www.highfrequencyelectronics....104_Sevick.pdf Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap transformer which provides 50/75 ohm connections/substitutions. Perfect for allowing one to use 75 ohm "junk" (or found in dumpsters) tv coax in place of more expensive 50 ohm coax. I have made good use of this since I have thousands of feet of NEW 75 ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of large dia coax and hard-line mixed in! Regards, JS A little mismatch isn't such a problem. At least if you can get the loss down. I wouldn't even worry about it, the internal tuner would make short work of that. Look out for water damage on that stuff though. Especially the Aluminum braid/foil shield stuff like LMR. Even a little bit of moisture percolates all through the braid.and turns it into aluminum oxide powder and extremely noisy with power on it. It could look brand new and you would keep cutting it back, then find a foot of new braid but keep cutting and its back to chalk. We would routinely assume it bad and throw it away. At least with the Hardline, you can sweep it and put some power to it to check the loss Only hardline allowed on towers. |
Baluns?
JB wrote:
... A little mismatch isn't such a problem. At least if you can get the loss down. I wouldn't even worry about it, the internal tuner would make short work of that. Look out for water damage on that stuff though. Especially the Aluminum braid/foil shield stuff like LMR. Even a little bit of moisture percolates all through the braid.and turns it into aluminum oxide powder and extremely noisy with power on it. It could look brand new and you would keep cutting it back, then find a foot of new braid but keep cutting and its back to chalk. We would routinely assume it bad and throw it away. At least with the Hardline, you can sweep it and put some power to it to check the loss Only hardline allowed on towers. Since it was on spools, and dusty, had no concern with that. LOL Regards, JS -- It is like a nightmare where the public servants are people which the police are supposed to protect you from! |
Baluns?
Owen wrote:
... Did you mean a two core design onto one core? Here is an analysis of the single core version: http://www.vk1od.net/balun/gsc/index.htm . Guanella did not show the 4:1 balun on a shared magnetic circuit, and it is an error on the part of those who think that the two independent TLTs in Guanella's circuit can be coupled without changing the behaviour significantly (basically, ruining it). Owen Let's cut the crap, currents in one winding which cause lines of force in the toroid/ferrite-core, should only assist the lines of force generated in the core by the other winding on the opposite side of the core--in the single core model of the guanella balun--composed of two 1:1s in a 1:4 configuration (or guanella TLT, since you seem to prefer acronyms.) At least TLT get the transmission line requirement out in the open ... Since toroids naturally demonstrate "economy of loss" in the magnetic lines of force within their structure, few, if any, lines of force would be shared between two separate cores, stacked. Now, wasn't it Einstein who recommended that things only be made as complex as necessary and not one iota more?--Or, watch out for the gray haired man who keeps attempting to sneak behind the curtains in this train ride though Oz--and KEEP HIM AWAY FROM THE LEVERS! ;-P Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Baluns?
On Sep 1, 9:52*pm, Owen Duffy wrote:
wrote in news:6f4f9e36-af26-4f1b-9244-383494f77b26 @c58g2000hsc.googlegroups.com: On Sep 1, 3:25*pm, Cecil Moore wrote: wrote: ... Actually, 1000 ohms is pretty liberal. For instance, on 15m, the G5RV coax sees 36+j230 ohms or about 233 ohms. The balun needs to be 10x that value or 2330 ohms. -- 73, Cecil *http://www.w5dxp.com Why not 500 ohms, assuming a 50 ohm source and transmission line? The common mode impedance of the balun acts in the common mode transmission line (which is mutually coupled to the nominal radiator). How is the differential mode transmission line characteristic impedance relevant to the determination of common mode current in the antenna system scenario described? Owen For a balanced transmission line, the characteristic impedance is not expressed in differential mode terms, it IS common mode so I do not know why you ask about differential mode characteristic impedance. I never mentioned it. The characteristic impedance of a ladder line for example might be expressed as 600 ohms. That 600 ohms assumes common mode conduction, as charateristically transmitted in a balanced line, Differential mode impedance is assumed for un balanced transmission line conditions. |
Baluns?
On Sep 2, 7:26*am, Cecil Moore wrote:
wrote: Yes and I have to partially take back what I said; a balun CAN double as a CM "choke" and a CM choke can double as a balun. If one wishes to balance an unbalanced line with a CM choke, then the impedance of the CM choke must match the source and the load, which makes the CM choke a balun and no longer a choke :-) Actually, a balun without a large choking impedance is not very useful for ham antenna system applications. The method that a W2DU balun uses to balance currents at a dipole feedpoint *IS* nothing more than a large choking impedance which discourages common-mode current from flowing through the higher-the-better impedance. I usually refer to the W2DU balun as a choke-balun. -- 73, Cecil *http://www.w5dxp.com I disagree. There is no choking, there is merely a polarity and phase shift between the "primary" and "secondary" of the 1:1 balun "transformer". The best way I can easily express this is to consider a 1:1 240V 60 Hz isolation transformer (yes, the balun acts theoretically in the same manner). At the unbalanced input you connect 240V on one terminal and earthed neutral on the other terminal. Now consider the isolated secondary each feeding an equal resistive load to the center tap of the secondary (analagous to radiation resistance). Across each load we see 120V, 180 degrees out of phase. This is a balanced transmission. Correct, this is not RF but it illustrates what the balun is supposed to be doing. There is NO choking function at all if it is working properly. There cannot be a choke when impedances are matched, only when they are significantly mismatched. |
Baluns?
On Sep 2, 7:51*am, Cecil Moore wrote:
wrote: On Sep 1, 3:25 pm, Cecil Moore wrote: Actually, 1000 ohms is pretty liberal. For instance, on 15m, the G5RV coax sees 36+j230 ohms or about 233 ohms. The balun needs to be 10x that value or 2330 ohms. Why not 500 ohms, assuming a 50 ohm source and transmission line? Be the current making a choice of paths at a junction. How much of you would flow through 500 ohms and how much would flow through 233 ohms? (If 500 ohms is the total impedance seen by the shield current looking back toward the source, about 1/3 of the current would flow back through the 500 ohms down the coax.) http://eznec.com/Amateur/Articles/Baluns.pdf -- 73, Cecil *http://www.w5dxp.com I got confused as to whether we were talking "choke" or "balun". For the balun, you want to be as close to 50 ohms as possible. Actually 233 ohms is not that bad. 1K would be really bad and illustrate that the balun is not working well. It 233 ohms, it is sort of OK, especially with a tuner, which you use with a G5RV anyway, along with the ugly balun. In priciople, the frequency works OK for my G5RV/ugly balun system. By the way, I have seen so many articles about baluns written by other hams and they tend to repeat the same mistakes and assumptions. Most hams do not understand how a balun works. Some even think you do not need a balun if the antenna is at resonance which is totally untrue. Anytime you feed a dipole directly with an unbalanced coax, the balanced dipole "load" forces current down your ground shield and into your radio and makes your radio part of your transmitting antenna. Inserting a balun does not "choke" the current in the shield, it merely shifts the output phases so that the current (voltage) is directed towards the dipole at all times (see my other post in this thread). |
Baluns?
On Sep 2, 10:22*am, Ian White GM3SEK wrote:
Dan wrote: On Sep 1, 4:20*am, Ian White GM3SEK wrote: Dan wrote: On Aug 31, 3:07*pm, Ian White GM3SEK wrote: Dan wrote: On Aug 28, 2:26*am, Ian White GM3SEK wrote: In other words, people with limited antenna opportunities are often the ones who need a balun - or more accurately, a common-mode choke - the MOST. Technically I would have to disagree with calling even a 1:1 balun the same thing as a common mode choke. *A CM choke is an EMI prevention device intended to filter out RF components generated in a circuit, away from the feed of a power source, usually an electrical mains. That is too far narrow a definition *of a "common mode choke", especially the reference to electrical mains. The term is widely applied to transmission line for both digital data and analog RF signals. A common mode choke is used in RF applications, very true, but it serves a filtering purpose, not a conversion of unbalanced to balanced energy transfer or vice versa. A common mode choke that operates well will turn unwanted RF into heat or cause it to dissipate in its core or a resistor etc.. Common-mode chokes, and filters in general, do NOT aim to "turn unwanted RF into heat"! That is a total misunderstanding of the whole concept. A CM choke aims to present a high impedence to unintentional RF. Once "choked" by the high impedance, the enrgey must either reflect or be aborbed somewhere in the circuit or the core as real power. What is it that you cannot understand about the term "choke"? I'm slightly encouraged that the key word "reflected" has now crept into your description. It wasn't there in what you wrote previously. [Snip similar] In a perfect situation, with a balanced feedline, the only kind of current and voltage you have IS common mode! What??? *You know that statement didn't come out right, so how much of the rest did you really mean? I give up! You need some education in this area. I give up too - *at last, something we can agree about. My main worry is that anyone *else* might have tried to gain some education from your confused statements on this particular topic. -- 73 from Ian GM3SEK * * * * 'In Practice' columnist for RadCom (RSGB)http://www.ifwtech.co.uk/g3sek- Hide quoted text - - Show quoted text - Many US amateurs do not understand how a balun works. I expected something better from our European counterparts who seem to understand power transmission concepts better than their US counterparts. |
Baluns?
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Baluns?
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Baluns?
In message , John Smith
writes JB wrote: ... There ya go. One of the problems of breaking up the path to ground on the shield is that now static can build up. If you can provide a way to bleed off the charges that build up on both halves, while breaking up the shield currents, now you have made it worthwhile. But when you guys start discussing off center fed dipoles, I step aside. I have computers in the shack. I have better luck with fan dipoles. Also running a Butternut vertical. Works a lot better than a 4btv, but a pain to get it right on all bands. Thanks Also liked the other pdfs presented. I never have time to read them all because of constant interruption around here. Back to work. OCF antennas were not fully appreciated by me, a few of Cecils' helpful insights and encouragement and I built one and was rather surprised ... I do not have one right now but that is only due to neighbors/property constraints. Here is a URL for design/implementation of "non-standard" baluns/transformers, but of a highly useable and desirable nature--or, Dr. Sevick strikes again!: http://www.highfrequencyelectronics....104_Sevick.pdf Fig. 6(A) is very interesting. A 5-winding, 1:1.56 bootstrap transformer which provides 50/75 ohm connections/substitutions. Perfect for allowing one to use 75 ohm "junk" (or found in dumpsters) tv coax in place of more expensive 50 ohm coax. I have made good use of this since I have thousands of feet of NEW 75 ohm coax I purchased from a scrap dealer for next-to-nothing! A lot of large dia coax and hard-line mixed in! Regards, JS What about the loss in the balun? You need to decide if the loss in the balun is less than that you would get if you simply used the 75 ohm coax direct. And ask yourself 'In my application, why would 75 ohm be more lossy?' Also, with similar physical dimensions, construction etc, 75 ohm coax is slightly less lossy than 50 ohm (current is less, so 'I squared R' loss is less). -- Ian |
Baluns?
Ian Jackson wrote:
... What about the loss in the balun? You need to decide if the loss in the balun is less than that you would get if you simply used the 75 ohm coax direct. And ask yourself 'In my application, why would 75 ohm be more lossy?' Also, with similar physical dimensions, construction etc, 75 ohm coax is slightly less lossy than 50 ohm (current is less, so 'I squared R' loss is less). Simple solution, I trust my S-meter! Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Baluns?
Richard Clark wrote:
... How true - not even fundamental terminology. 73's Richard Clark, KB7QHC When you are right, you are right; and, YOU GOT THAT ONE RIGHT! :-) Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! |
Baluns?
wrote:
I disagree. There is no choking, there is merely a polarity and phase shift between the "primary" and "secondary" of the 1:1 balun "transformer". In a w2du balun, zero flux in the beads is introduced by the transmission line currents. All of the flux in the beads is introduced by common-mode currents. Thus the impedance of the beads *IS* a choking impedance aimed only at the common-mode currents. My choke-balun is ten turns of RG-400 on an FT-240-77 toroid. It's only purpose is to provide a choking impedance to common-mode current. That choke-balun doesn't know if it is being used as a UNUN or as a BALUN. Most baluns are designed such that near-zero flux is introduced in the ferrite toroid by the differential mode currents. Essentially, the only flux introduced in the toroid is due to common-mode. The resulting impedance *IS* a choking impedance. -- 73, Cecil http://www.w5dxp.com |
Baluns?
wrote:
By the way, I have seen so many articles about baluns written by other hams and they tend to repeat the same mistakes and assumptions. Most hams do not understand how a balun works. Your following statement puts you in that category. Inserting a balun does not "choke" the current in the shield, it merely shifts the output phases so that the current (voltage) is directed towards the dipole at all times (see my other post in this thread). This applies to a W2DU balun. Why would you want differential current fields to be introduced into the #77 ferrite beads? Their entire purpose is to provide a large choking impedance and dissipate common-mode power. -- 73, Cecil http://www.w5dxp.com |
Baluns?
wrote:
Many US amateurs do not understand how a balun works. Quoting "The ARRL Antenna Book" re a w2du balun: "Maxwell made a test balun by slipping 300 #73 beads over a piece of RG-303 coaxial cable. The impedance of the outer conductor of the cable measured 4500+j3800 at 4.0 MHz." The differential current emerging from the inside of the coax braid encounters, e.g. 30 ohms, looking toward the antenna. It encounters 4500+j3800 = 5890 ohms looking back down the outside of the coax. Ohm's law does the rest. Without the beads, that differential current might see an impedance lower than 30 ohms looking back down the outside of the coax for certain unfortunate lengths of coax. The common-mode choking impedance forces ~equal currents in each dipole leg at the BALanced antenna to UNbalanced coax junction. That common-mode choking impedance causes the balun function to occur. -- 73, Cecil http://www.w5dxp.com |
Baluns?
Cecil Moore wrote:
Most baluns are designed such that near-zero flux is introduced in the ferrite toroid by the differential mode currents. That should have been, "Most 1:1 current baluns ..." -- 73, Cecil http://www.w5dxp.com |
Baluns?
Richard Clark wrote:
wrote: Many US amateurs do not understand how a balun works. How true - not even fundamental terminology. http://en.wikipedia.org/wiki/Balun (see 1st photo) "This is a simple RF *choke* which works as a *balun* by preventing signals passing along the outside of the braid." From "The IEEE Dictionary": "balun (1) A network for the transformation from an unbalanced line or system to a balanced line or system, or vice versa." From an Unabridged Webster's: "balun - a device for converting a balanced line into an unbalanced line and vice versa." 10 PRINT "A W2DU balun is both a choke and a balun!" 20 Goto 10 -- 73, Cecil http://www.w5dxp.com |
Common and Differential Modalities
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Baluns?
On Sep 2, 10:43*pm, John Smith wrote:
wrote: ... I disagree. There is no choking, there is merely a polarity and phase shift between the "primary" and "secondary" of the 1:1 balun "transformer". The best way I can easily express this is to consider a 1:1 240V 60 Hz isolation transformer (yes, the balun acts theoretically in the same manner). ... No. *But you have focused on your error in thinking/logic/function. *An RF Transformers does what you state, lengths of transmission line carrying RF behave in a different "mode." (uh, I hate that word ...) Now, if you do some research, you can correct your error(s) ... Regards, JS -- It is like a nightmare where the public servants are the people which the police are supposed to protect us from! 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. |
Baluns?
On Sep 3, 7:18*am, Cecil Moore wrote:
wrote: For a balanced transmission line, the characteristic impedance is not expressed in differential mode terms, it IS common mode so I do not know why you ask about differential mode characteristic impedance. Well, there's your problem. In a properly functioning transmission line, whether balanced or unbalanced, the currents in the two conductors are differential, not common-mode. The two currents are equal in magnitude and 180 degrees out of phase and their fields tend to cancel which minimizes radiation. Common-mode currents only occur when the two currents are not perfectly differential, i.e. not equal amplitudes and/or not 180 degrees out of phase. -- 73, Cecil *http://www.w5dxp.com Nope. The CM choke works precisely because the common mode currents are mirror images, 180 degrees out of phase. If they weren't, the CM choke could not act to cancel them and you would need differential mode chokes to get rid of them. On your balanced feedline, the voltage at any point is delta between the amplitude of line 1 and 2. |
Baluns?
On Sep 3, 7:44*am, Cecil Moore wrote:
wrote: By the way, I have seen so many articles about baluns written by other hams and they tend to repeat the same mistakes and assumptions. Most hams do not understand how a balun works. Your following statement puts you in that category. Inserting a balun does not "choke" the current in the shield, it merely shifts the output phases so that the current (voltage) is directed towards the dipole at all times (see my other post in this thread). This applies to a W2DU balun. Why would you want differential current fields to be introduced into the #77 ferrite beads? Their entire purpose is to provide a large choking impedance and dissipate common-mode power. -- 73, Cecil *http://www.w5dxp.com OK, next time I specify an EMC filter for a switching power supply, I will ensure that the CM choke impedance matches the impedances of the network and the loads so that I can most efficiently conduct RFI from the source to the power line, from common mode at the load to unbalanced load of the power line source. This will ensure maximum interference is imparted on the phase conductor. In fact, I think I will change my nomenclature by refering to the "choke" as a "balun" (they are one and the same; the source doesn't know the difference!) and promptly fail my next FCC submittal. Then I will be invited to retire and of course I will have much more time to be re- educated on rec.radio.amareur.antenna. |
Baluns?
On Sep 3, 8:04*am, Cecil Moore wrote:
wrote: Many US amateurs do not understand how a balun works. Quoting "The ARRL Antenna Book" re a w2du balun: "Maxwell made a test balun by slipping 300 #73 beads over a piece of RG-303 coaxial cable. The impedance of the outer conductor of the cable measured 4500+j3800 at 4.0 MHz." The differential current emerging from the inside of the coax braid encounters, e.g. 30 ohms, looking toward the antenna. It encounters 4500+j3800 = 5890 ohms looking back down the outside of the coax. Ohm's law does the rest. Without the beads, that differential current might see an impedance lower than 30 ohms looking back down the outside of the coax for certain unfortunate lengths of coax. The common-mode choking impedance forces ~equal currents in each dipole leg at the BALanced antenna to UNbalanced coax junction. That common-mode choking impedance causes the balun function to occur. -- 73, Cecil *http://www.w5dxp.com 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. |
Baluns?
On Sep 3, 2:10*pm, Cecil Moore wrote:
Richard Clark wrote: wrote: Many US amateurs do not understand how a balun works. How true - not even fundamental terminology. http://en.wikipedia.org/wiki/Balun(see 1st photo) "This is a simple RF *choke* which works as a *balun* by preventing signals passing along the outside of the braid." *From "The IEEE Dictionary": "balun (1) A network for the transformation from an unbalanced line or system to a balanced line or system, or vice versa." *From an Unabridged Webster's: "balun - a device for converting a balanced line into an unbalanced line and vice versa." 10 PRINT "A W2DU balun is both a choke and a balun!" 20 Goto 10 -- 73, Cecil *http://www.w5dxp.com I agree that a balun operating at 14 MHz would be a choke when operating at 70MHz. |
Baluns?
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 |
Common and Differential Modalities
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. |
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 So that means I get 0 volts when I touch one side of the 120V in my electrical service to the 120V other side? I was afraid I might see 240V. |
Baluns?
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 |
Baluns?
wrote:
So that means I get 0 volts when I touch one side of the 120V in my electrical service to the 120V other side? I was afraid I might see 240V. If those signals are equal in amplitude and 180 degrees out of phase, it means they are *differential*, you will see 240v, and you had better not short them together. OTOH, if they are common-mode signals, they are in-phase and you can short them together to your heart's content - no current will flow. Again, you seem to have the IEEE definitions of "differential" and "common-mode" exactly reversed in your head. -- 73, Cecil http://www.w5dxp.com |
Baluns?
"JB" wrote in news:gQ2vk.206$Af3.111@trnddc06:
God's plan won't be usurped, but we can petition Him with prayer over some points. This leads us to another possible conclusion. 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 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. Nice guy. |
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. 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. |
Baluns?
On Sep 3, 7:25*pm, Cecil Moore wrote:
wrote: So that means I get 0 volts when I touch one side of the 120V in my electrical service to the 120V other side? I was afraid I might see 240V. If those signals are equal in amplitude and 180 degrees out of phase, it means they are *differential*, you will see 240v, and you had better not short them together. OTOH, if they are common-mode signals, they are in-phase and you can short them together to your heart's content - no current will flow. Again, you seem to have the IEEE definitions of "differential" and "common-mode" exactly reversed in your head. -- 73, Cecil *http://www.w5dxp.com Really? Do you believe the currents in a resonant 1/2 wave dipole are common mode or differential mode? |
Baluns?
Mike Coslo wrote:
"JB" wrote in news:gQ2vk.206$Af3.111@trnddc06: ... Nice guy. Wow, just imagine, some guy ( a God) claims to know all about "you." Ain't much of a claim huh, a complex mind would be much more difficult, huh? ROFLOL "He" might have to guess then ... ;-) 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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Baluns?
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Baluns?
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Common and Differential Modalities
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Common and Differential Modalities
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