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what a 1:1 choke balum used for
I picked up a 1:1 balum at a local hamfest, i got it because it had a
N connector and thats the type of connector on my coax. After looking closer i thought it was a 10-40 meter but i cant make out the print, it may be 10-40mhz. I desided to open the pvc to find out just what was inside, I found a bunch of ferrite disk stacked over the coax, this wasent my idea of a 1:1 balum. I hoped to make a 160-10 meter dipole/inverted vee using the proper length wire on each leg for 160,80,40 & 10. My question is this, will this work at lower frequencys 160 & 80m ? If not what the purpose of the ferrite disks, it seems that i could just remove the disk if they limit the frequency range, i guess im trying to inderstand what makes this a balum & what purpose the disk serve? |
what a 1:1 choke balum used for
wrote:
I desided to open the pvc to find out just what was inside, I found a bunch of ferrite disk stacked over the coax, this wasent my idea of a 1:1 balum. You have what is commonly known as a W2DU 1:1 balun-choke made popular by Walter Maxwell. It's probably not very effective on 80m and 160m because of the choice of ferrite materials. -- 73, Cecil http://www.qsl.net/w5dxp |
what a 1:1 choke balum used for
Cecil Moore wrote:
wrote: I desided to open the pvc to find out just what was inside, I found a bunch of ferrite disk stacked over the coax, this wasent my idea of a 1:1 balum. You have what is commonly known as a W2DU 1:1 balun-choke made popular by Walter Maxwell. It's probably not very effective on 80m and 160m because of the choice of ferrite materials. If you can get an ohm reading when you touch the two probes of an ohm meter to the ferrite, then it is probably a low frequency, high permeability manganese zinc ferrite, and may produce enough common mode impedance to act effectively as a 1:1 balun in this frequency range. If you measure an open circuit, it is almost certainly higher frequency, lower permeability nickel zinc ferrite and will produce insufficient common mode impedance to be effective as a balun in this frequency range. |
what a 1:1 choke balum used for
It is used to reduce the common mode current which sometimes flows in
coaxial and balanced-pair lines. It is not a transformer. The 1-to-1 is meaningless. It is just a pair of wires wound together, as one wire, on a ferrite core. Or in your case a number of ferrite slugs or rings are placed over a coax line. In brief, it is just a choke. ---- Reg. |
what a 1:1 choke balum used for
Reg Edwards wrote:
It is used to reduce the common mode current which sometimes flows in coaxial and balanced-pair lines. It is not a transformer. The 1-to-1 is meaningless. It is just a pair of wires wound together, as one wire, on a ferrite core. Or in your case a number of ferrite slugs or rings are placed over a coax line. In brief, it is just a choke. But a choke with two wires wound through it is two inductors that also have mutual inductance between them, and if that doesn't define a transformer, what does? It is true that this device acts as a choke for common mode current (the component of the two currents through the two conductors that is in phase). A choke is an inductance, which produces voltage across the terminals of the conductor passing through that is proportional to the rate of change of the current. In this case, it produces a voltage across both the shield section inside the cores and also across the center conductor inside the cores, that is proportional to the rate of change of the common mode current. It is this voltage that alters the displacement currents in the two terminals at the antenna end, to make them look like a more balanced signal, and at the transmission line end, more like a single ended one. |
what a 1:1 choke balum used for
On Tue, 28 Mar 2006 12:05:01 -0500, John Popelish
wrote: But a choke with two wires wound through it is two inductors that also have mutual inductance between them, and if that doesn't define a transformer, what does? Hi John, Then you think of it as an air core transformer with series driven, bucking sections. Now, what kind of practical transformer does that define? 1:1 does not automatically spring to mind unless it is isolating one circuit from the other. However, it is not the transformer that does that, it is the choking ferrite and only in the service of snubbing common mode currents. With this in mind, do we add a characteristic of loss to the definition? A lossy air core transformer with series driven, bucking sections. You are bordering on stretching the definition of power transformer over the application of a BalUn. This is not always useful. So, what does it transform? A balanced circuit to an unbalanced circuit (or versa vice). 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
Reg Edwards wrote:
In brief, it is just a choke. And a Balun if there is enough choking action. -- 73, Cecil http://www.qsl.net/w5dxp |
what a 1:1 choke balum used for
Richard Clark wrote:
On Tue, 28 Mar 2006 12:05:01 -0500, John Popelish wrote: But a choke with two wires wound through it is two inductors that also have mutual inductance between them, and if that doesn't define a transformer, what does? Hi John, Then you think of it as an air core transformer with series driven, bucking sections. Now, what kind of practical transformer does that define? 1:1 does not automatically spring to mind unless it is isolating one circuit from the other. However, it is not the transformer that does that, it is the choking ferrite and only in the service of snubbing common mode currents. With this in mind, do we add a characteristic of loss to the definition? A lossy air core transformer with series driven, bucking sections. Air core? It is a ferrite core transformer with two one turn windings. One winding is the shield passing through the holes in the cores and the other winding is the center conductor passing through the windings. (view with fixed width font, like Courier) |half of dipole . | Center cond.-----MMMM-+ |
what a 1:1 choke balum used for
I mainly wanted to know if it would work on 160 & 80m, I dont care
if it acts like a choke/balun only at higher frequencys as long as as it doesnt interfere with 160 & 80s swr. Normally i just use coax hooked to each leg cut to frequency, without a balun. Its allways worked in the past years, i just thought it would be alot easier to use the ready made balun than try and makeup a weatherproof hanger |
what a 1:1 choke balum used for
In article . com,
wrote: I mainly wanted to know if it would work on 160 & 80m, I dont care if it acts like a choke/balun only at higher frequencys as long as as it doesnt interfere with 160 & 80s swr. It should not interfere. If the ferrites don't have enough reactance to make it act as an effective choke on 160/80, then it'll just "look like" a foot or two of coax to the signals. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
what a 1:1 choke balum used for
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what a 1:1 choke balum used for
On Tue, 28 Mar 2006 12:59:52 -0500, John Popelish
wrote: With this in mind, do we add a characteristic of loss to the definition? A lossy air core transformer with series driven, bucking sections. Air core? It is a ferrite core transformer with two one turn Hi John, If there's a transformer in the sense of windings; then it is an air core, the ferrite is wholly transparent to the transverse currents. You could remove the ferrite and it wouldn't make a bit of difference in that sense of transforming. this current mismatch would cause the transformer to produce more or less voltage across the windings In fact, nothing of that sort happens - at least not by your description. The ferrite is simply bulk resistance inserted into the common mode path. That is why common mode current is suppressed. The same thing occurs in the coiled transmission line choke, but the resistance is replaced by reactance. Again, common mode current is snubbed by encountering this too. The transformer property is in the isolation of the balanced circuit from the unbalanced circuit through this resistive characteristic. You are missing one path. The two from the source in the form of the inner shield of the coax, and the center conductor, and the one from the load in the form of the outer shield of the coax (same shield, but isolated circuits). Further, there is no flux linkage of the two conductors coming from the source. Their magnetic lines never break the cores, whereas the common mode current does break the core which thus inserts the resistance of the ferrite. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
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what a 1:1 choke balum used for
On Tue, 28 Mar 2006 17:39:52 -0800, Richard Clark
wrote: Further, there is no flux linkage of the two conductors coming from the source. That was not correctly expressed, the flux between the two are tightly bound and: Their magnetic lines never break the cores, whereas the common mode current does break the core which thus inserts the resistance of the ferrite. |
what a 1:1 choke balum used for
John I will have to take it down and measure it, im going to do it
anyway because the balun will not load up like it should even with wire on each leg cut to the proper length. I dosent dip with the dip meter at the proper freq either, after i take it down ill post the ohmeter results. |
what a 1:1 choke balum used for
Richard Clark wrote:
On Tue, 28 Mar 2006 12:59:52 -0500, John Popelish wrote: Air core? It is a ferrite core transformer with two one turn Hi John, If there's a transformer in the sense of windings; then it is an air core, the ferrite is wholly transparent to the transverse currents. I said that. It is a common mode transformer. You could remove the ferrite and it wouldn't make a bit of difference in that sense of transforming. The short length of the two conductors passing through the ferrite is certainly a poorer transformer (less mutual inductance between them) if you remove the cores. this current mismatch would cause the transformer to produce more or less voltage across the windings In fact, nothing of that sort happens - at least not by your description. The ferrite is simply bulk resistance inserted into the common mode path. Make that, "impedance (mostly inductive, if the ferrite is well suited to the frequency)" and I agree. That is why common mode current is suppressed. The same thing occurs in the coiled transmission line choke, but the resistance is replaced by reactance. Again, common mode current is snubbed by encountering this too. I agree with this, except that the purpose of the ferrite is to increase the common mode inductance of the section of coax passing through it, not add resistance. Some resistance is inevitable, because no ferrite is lossless, but the intention is for inductance. The transformer property is in the isolation of the balanced circuit from the unbalanced circuit through this resistive characteristic. Try transmitting through such a resistance and you are going to lose a lot of your power. You are missing one path. The two from the source in the form of the inner shield of the coax, and the center conductor, and the one from the load in the form of the outer shield of the coax (same shield, but isolated circuits). I can't parse this. There are two metal conductors entering the choke, and two exiting it. All currents pass through those 4 conductors. Further, there is no flux linkage of the two conductors coming from the source. Their magnetic lines never break the cores, I think you mean by this that a normal unbalanced signal in a coax has no magnetic field external to the shield. It is all between the center conductor and the shield. And I agree that this is what you are trying to accomplish by adding this two conductor choke between the coax and the balanced antenna. Without it, there would be some magnetic field from a net (uncanceled) current and voltage on the outside of the shield that would cause the coax to radiate. And the voltages and currents fed to the balanced antenna would not be equal and opposite (balanced) but somewhat unbalanced. There would also be non equal currents in the center conductor and shield. I think we agree on all that, but have a different picture of how a choke balun corrects these problems. whereas the common mode current does break the core which thus inserts the resistance of the ferrite. The common mode current causes flux in the core, and the conductors passing through that flux produce a voltage proportional to the rate of change of that flux, just as the conductor passing through any inductor would. The transformer aspect is that since both conductors pass through the exact same rate of change of flux, there is the same voltage produced at the ends sticking out of the core, and this voltage gets algebraically added to what is already there. If the inductance of each winding is high enough (5 to 10 times the coax impedance) a very small common mode current is enough to produce a large enough voltage across the ends to the two conductors to correct most of the unbalanced to balanced coupling. Admittedly, there is no need to get this inductance (including mutual inductance) with the aid of ferrite around the coax. You could just wind the coax into an air core transformer. But it would be considerable larger than one made with a high permeability core, though, probably lower loss. |
what a 1:1 choke balum used for
John Popelish wrote:
Richard Clark wrote: . . . In fact, nothing of that sort happens - at least not by your description. The ferrite is simply bulk resistance inserted into the common mode path. Make that, "impedance (mostly inductive, if the ferrite is well suited to the frequency)" and I agree. "Low frequency" ferrites are well suited to applications as HF chokes and broadband transformers. What you don't want to do is use them for a high Q inductor in a filter, tuned circuit, or similar application. That is why common mode current is suppressed. The same thing occurs in the coiled transmission line choke, but the resistance is replaced by reactance. Again, common mode current is snubbed by encountering this too. I agree with this, except that the purpose of the ferrite is to increase the common mode inductance of the section of coax passing through it, not add resistance. Some resistance is inevitable, because no ferrite is lossless, but the intention is for inductance. Baluns work fine with a resistive impedance, with the exception of applications involving large power. In fact, resistive impedance is desirable because the impedance changes little with frequency, and is relatively free of resonance effects. (More below.) The transformer property is in the isolation of the balanced circuit from the unbalanced circuit through this resistive characteristic. Try transmitting through such a resistance and you are going to lose a lot of your power. You're not "transmitting through" a balun's impedance. Only the common mode current effectively flows through it, and the power dissipated by the balun is Icm^2 * R, where Icm is the common mode current and R is the resistive part of the balun's common mode impedance. If R is small, dissipation is low. But if R is large, that makes Icm small, so dissipation is also low. It's really an impedance matching problem when the balun is resistive -- a very low or very high balun R results in low dissipation. Dissipation is maximum at some intermediate value of R and decreases on each side. A typical balun made with "low frequency" ferrite (e.g. Fair-Rite 70 series) and operating at HF or above (and therefore primarily resistive) having a common mode impedance of 500 ohms or greater generally won't dissipate any significant fraction of the transmitted power. However, if you're running high power, even a fraction of a dB dissipated in the balun will cause it to overheat. Consequently, people running high power often resort to type 43 ferrite (a Fair-Rite designation; or its equivalent from other manufacturers), which is less resistive than lower frequency ferrites. In extreme cases, high frequency (60 series) ferrite is necessary. The problem is that it's increasingly difficult to get adequate impedance with the higher frequency ferrites. Type 43 is often a good compromise, and it's widely available in many core sizes. . . . I think you mean by this that a normal unbalanced signal in a coax has no magnetic field external to the shield. It is all between the center conductor and the shield. And I agree that this is what you are trying to accomplish by adding this two conductor choke between the coax and the balanced antenna. Without it, there would be some magnetic field from a net (uncanceled) current and voltage on the outside of the shield that would cause the coax to radiate. And the voltages and currents fed to the balanced antenna would not be equal and opposite (balanced) but somewhat unbalanced. There would also be non equal currents in the center conductor and shield. I think we agree on all that, but have a different picture of how a choke balun corrects these problems. . . . Common and differential mode currents are physically separated in a coax cable, and so are the fields from the two components, providing that the shield is at least several skin depths thick. The differential mode current and its fields are entirely inside the coax, decaying rapidly as you go outward from the inner boundary of the shield. By the time you reach the outer boundary of the shield the fields from the differential current is negligibly small. So any core you put over the coax doesn't see or interact with the common mode current or its fields at all, and you can completely ignore it when analyzing balun action. Similarly, you can ignore the core when analyzing the differential mode properties of the system. The common mode current resides in a thin layer on the outside of the shield, it and its fields never reaching the inside. The balun provides an impedance to this current just as it would to any current on the outside of a conductor. When bifilar wound, the fields from the differential mode current are primarily between the turns, although some relatively small amount extends beyond to interact with the core. The net result is nearly the same. . . . Roy Lewallen, W7EL |
what a 1:1 choke balum used for
Roy Lewallen wrote:
So any core you put over the coax doesn't see or interact with the common mode current or its fields at all, and you can completely ignore it when analyzing balun action. Roy probably meant "differential" above instead of "common". Cores on coax definitely "interact with the common mode current or its fields" and that is their purpose. -- 73, Cecil http://www.qsl.net/w5dxp |
what a 1:1 choke balum used for
On Tue, 28 Mar 2006 22:33:18 -0500, John Popelish
wrote: this current mismatch would cause the transformer to produce more or less voltage across the windings In fact, nothing of that sort happens - at least not by your description. The ferrite is simply bulk resistance inserted into the common mode path. Make that, "impedance (mostly inductive, if the ferrite is well suited to the frequency)" and I agree. Hi John, No, the principle of the impedance is overwhelmingly resistive, not reactive. One core (#75) that snuggly fits over RG58, at about 10MHz, exhibits 25 Ohms resistance to common mode current. My BalUn uses 50 such whose combination presents 1250 Ohms resistance. This value varies over frequency, but easily finds a 1000:50 ratio over the entire MF/HF Ham spectrum. I also have two engineering samples boxes full of various material types and geometries and have measured them all. Some exhibit reactance, but are vastly overwhelmed by their intrinsic resistance. That is why common mode current is suppressed. The same thing occurs in the coiled transmission line choke, but the resistance is replaced by reactance. Again, common mode current is snubbed by encountering this too. I agree with this, except that the purpose of the ferrite is to increase the common mode inductance of the section of coax passing through it, not add resistance. Some resistance is inevitable, because no ferrite is lossless, but the intention is for inductance. Quite the contrary. Inductance, or more properly to the application, reactance, may come as a consequence of these cores, but that is really just a minor component to the vastly greater resistance. The transformer property is in the isolation of the balanced circuit from the unbalanced circuit through this resistive characteristic. Try transmitting through such a resistance and you are going to lose a lot of your power. That power, actually current, was forced into a common mode because of one of several problems: 1. Massive imbalance in the radiator design, 2. Massive catastrophe with the radiator. If you are destined to "lose a lot of power" into such resistance, you have far greater problems you are ignoring. However, let's return to this "loss of a lot of power." You have an antenna with a nominal 50 Ohm load resistance (presumably balanced to the common). You have a common mode choke with 1000 Ohms resistance in parallel (to the common of the common mode). Now, why would the power choose the path of 10 to 40 times more resistance to invest its calories in? I will be generous and pour 1.5KW into a balanced 50 Ohm load to develop 275V that is also across the 1000 Ohms of the BalUn. 76W into 50 beads. Now this verges on serious power for this load I will admit, but it also presumes key-down conditions which would only be found for RTTY or SSTV. By my bench measurements, I figure that the core's can tolerate as much power as the bulk equivalent carbon composition resistor - or least this is my rule of thumb. This means about 1 or 2W per bead to offer enough heat to cause pain, but perhaps not enough to blister. This is another benchmark from my days in the Navy. I once asked an ET Chief how much heat a transistor could tolerate. He said "If you can hold onto it and count to 10, it's not too much." I've been blistered by TO-5 cans with just a casual brush and they still filled their design mission. You are missing one path. The two from the source in the form of the inner shield of the coax, and the center conductor, and the one from the load in the form of the outer shield of the coax (same shield, but isolated circuits). I can't parse this. There are two metal conductors entering the choke, and two exiting it. All currents pass through those 4 conductors. Your count is four terminals (not conductors), there are six. You need to come to terms with this shortfall in your count as it explains the utility and design of BalUns. Further, there is no flux linkage of the two conductors coming from the source. Their magnetic lines never break the cores, I think you mean by this that a normal unbalanced signal in a coax has no magnetic field external to the shield. It is all between the center conductor and the shield. And I agree that this is what you are trying to accomplish by adding this two conductor choke between the coax and the balanced antenna. Without it, there would be some magnetic field from a net (uncanceled) current and voltage on the outside of the shield that would cause the coax to radiate. And the voltages and currents fed to the balanced antenna would not be equal and opposite (balanced) but somewhat unbalanced. There would also be non equal currents in the center conductor and shield. I think we agree on all that, but have a different picture of how a choke balun corrects these problems. That is apparent. whereas the common mode current does break the core which thus inserts the resistance of the ferrite. The common mode current causes flux in the core, and the conductors passing through that flux produce a voltage proportional to the rate of change of that flux, just as the conductor passing through any inductor would. This "rate of change" is spurious, call it frequency dependant, but then frequency dependency is neither here nor there at this moment. More to the matter trying to turn this BalUn into a power transformer is doomed in this analysis as it has absolutely no impact to correct most of the unbalanced to balanced coupling. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
Richard Clark wrote:
On Tue, 28 Mar 2006 22:33:18 -0500, John Popelish wrote: (snip) Make that, "impedance (mostly inductive, if the ferrite is well suited to the frequency)" and I agree. Hi John, No, the principle of the impedance is overwhelmingly resistive, not reactive. One core (#75) that snuggly fits over RG58, at about 10MHz, exhibits 25 Ohms resistance to common mode current. Yep. Type 75 operated at 10MHz is very lossy. My BalUn uses 50 such whose combination presents 1250 Ohms resistance. This value varies over frequency, but easily finds a 1000:50 ratio over the entire MF/HF Ham spectrum. Thank you for some specific facts. I had no idea that you were using a ferrite whose permeability falls to half the low frequency value (about 5000 at 200kHz) at only 700kHz and is not recommended for flux coupling applications higher than about 750kHz. It also has a very low bulk resistivity of 300 ohm cm. At 3 MHz, its permeability is only about 150 (and plunging). Type 43 material has a permeability of about 500 at 3 MHz and falling much more slowly. I also have two engineering samples boxes full of various material types and geometries and have measured them all. Some exhibit reactance, but are vastly overwhelmed by their intrinsic resistance. (snip) I agree with this, except that the purpose of the ferrite is to increase the common mode inductance of the section of coax passing through it, not add resistance. Some resistance is inevitable, because no ferrite is lossless, but the intention is for inductance. Quite the contrary. Inductance, or more properly to the application, reactance, may come as a consequence of these cores, but that is really just a minor component to the vastly greater resistance. If the cores don't have relative hi permeability (causing mutual inductance in the two conductors passing through) they can't produce any impedance in series with the common mode current. That is also transformed over to the two conductors by mutual inductance (as a loaded secondary reflected to those conductors as a primary). Try transmitting through such a resistance and you are going to lose a lot of your power. That power, actually current, was forced into a common mode because of one of several problems: 1. Massive imbalance in the radiator design, 2. Massive catastrophe with the radiator. If you are destined to "lose a lot of power" into such resistance, you have far greater problems you are ignoring. However, let's return to this "loss of a lot of power." You have an antenna with a nominal 50 Ohm load resistance (presumably balanced to the common). You have a common mode choke with 1000 Ohms resistance in parallel (to the common of the common mode). Now, why would the power choose the path of 10 to 40 times more resistance to invest its calories in? I will be generous and pour 1.5KW into a balanced 50 Ohm load to develop 275V that is also across the 1000 Ohms of the BalUn. 76W into 50 beads. Now this verges on serious power for this load I will admit, but it also presumes key-down conditions which would only be found for RTTY or SSTV. By my bench measurements, I figure that the core's can tolerate as much power as the bulk equivalent carbon composition resistor - or least this is my rule of thumb. This means about 1 or 2W per bead to offer enough heat to cause pain, but perhaps not enough to blister. This is another benchmark from my days in the Navy. If the radiator is perfectly balanced, the impedance of the ferrite (transformed to the primary side) sees half of the voltage that is between the center conductor and the shield. So if the coax carries 275 volts, half of that or about 1378 volts appears across the bead bead common mode impedance. So a 1000 ohm common mode choke limits the common mode current to 138/1000 = 138 mA. And if that impedance is dominated by resistance, the beads will absorb 138*.138=19 watts. 50 beads will stand that indefinitely. I don't think the O.P.'s balun has 50 beads, though. You are missing one path. The two from the source in the form of the inner shield of the coax, and the center conductor, and the one from the load in the form of the outer shield of the coax (same shield, but isolated circuits). I can't parse this. There are two metal conductors entering the choke, and two exiting it. All currents pass through those 4 conductors. Your count is four terminals (not conductors), there are six. You need to come to terms with this shortfall in your count as it explains the utility and design of BalUns. If the other two are the ends of the loss resistance, they can be transformed back to the two conductors. (snip) The common mode current causes flux in the core, and the conductors passing through that flux produce a voltage proportional to the rate of change of that flux, just as the conductor passing through any inductor would. This "rate of change" is spurious, call it frequency dependant, but then frequency dependency is neither here nor there at this moment. More to the matter trying to turn this BalUn into a power transformer is doomed in this analysis as it has absolutely no impact to It may not be the approach you are familiar with, but I think it is valid. The transformer just has a lot of core loss, if you use a ferrite optimized for a much lower frequency. And that loss shows up as if it were a resistor connected across the ends of the two windings. If a low loss ferrite (at the operating frequency) is used, then the impedance across the windings is dominated by inductance, as one normally expects with a transformer. But the analysis handles the whole range of cases. |
what a 1:1 choke balum used for
On Wed, 29 Mar 2006 10:45:05 -0500, John Popelish
wrote: It may not be the approach you are familiar with, but I think it is valid. The transformer just has a lot of core loss, if you use a ferrite optimized for a much lower frequency. And that loss shows up as if it were a resistor connected across the ends of the two windings. If a low loss ferrite (at the operating frequency) is used, then the impedance across the windings is dominated by inductance, as one normally expects with a transformer. But the analysis handles the whole range of cases. Hi John, Through these last comments, and those that go before, you have entirely missed the boat of both the dynamics involved (this is not a magnetic circuit being described, and there are NO magnetic lines broken in a typical circuit in a balanced configuration), and the topology. Specifically to this last, you still do not seem to comprehend that a coax has three conductors and is a six terminal device. Roy has also commented to these issues and I think you should review his correspondence and respond to him. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
On Wed, 29 Mar 2006 17:01:51 GMT, rocky wrote:
To sort of sum things up, then what should I use for a choke balun on 75 meters, 77, 73 or 43 mix? More the better? I read the W2DU article and he used 73, but I thought 77 may be better? Hi OM, More is better? What do you seek to achieve that is not already answered by Walt's article? Didn't he specify which type? #64 material is going to offer about 3 Ohms per bead; #43 material is going to offer about 8 Ohms per bead; #73 & 77 material is going to offer about 18 Ohms per bead; #75 material is going to show offer 28 Ohms per bead. If you are running power into a matched load, you may want more of the lower resistance beads. If you are running barefoot, fewer more resistive beads will work. Or you could do it the old-fashion way by looping your coax at the drive point. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
John Popelish wrote:
. . . It may not be the approach you are familiar with, but I think it is valid. The transformer just has a lot of core loss, if you use a ferrite optimized for a much lower frequency. And that loss shows up as if it were a resistor connected across the ends of the two windings. If a low loss ferrite (at the operating frequency) is used, then the impedance across the windings is dominated by inductance, as one normally expects with a transformer. But the analysis handles the whole range of cases. Broadband transformers, which can operate well over several decades of frequency, commonly use ferrite cores which are essentially resistive over most of the operating frequency range. The sign of the impedance is unimportant to the transformer's operation; all that's necessary is that its magnitude be adequately high over the operating range (and of course that the core's permeability be adequately high). The wide band high impedance requirement is virtually impossible to meet with an inductive core whose impedance is approximately proportional to frequency, but easily done with cores whose impedance is essentially resistive. Roy Lewallen, W7EL |
what a 1:1 choke balum used for
On Wed, 29 Mar 2006 18:50:04 GMT, rocky wrote:
I run up to a KW, dipole and could be using an antenna tuner to stretch the bandwidth. I was just thinking if it could be made even more effective by using other bead material. Looks like #75 offers the best attenuation at 75 M. but if I am getting this right, it will heat up more under high power and off resonance. Hi OM, Think of the beads as series 1W resistors. Ask yourself how much of a common mode load they will present to the antenna "as a source" (this means that the dipole will look like a KW source with complex impedance). You then have to judge the potential that source will present in Common Mode to the beads. Elsewhere in this thread I've done a simplified analysis that suggests 50 #75 beads will get a tad hot under matched conditions because they are dissipating roughly 1.5W each. "Hot" is of little consequence until we shatter the ceramic because of thermal stress (the sintered product contains bulk irregularities). That stress could be arguably applied through a rain drop hitting a bead. Then we get into new issues of balance and symmetry because one part of the bead is cooler than the other. ;-) If, instead for this matched load, you replace the 50 #75 beads with 80 #73 or #77 beads; then you have roughly the same total resistance, but the heat dissipation (still 1W suggested load for each) is spread out more. Again, moving off resonance demands another analysis. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
Richard Clark wrote:
On Wed, 29 Mar 2006 10:45:05 -0500, John Popelish wrote: It may not be the approach you are familiar with, but I think it is valid. The transformer just has a lot of core loss, if you use a ferrite optimized for a much lower frequency. And that loss shows up as if it were a resistor connected across the ends of the two windings. If a low loss ferrite (at the operating frequency) is used, then the impedance across the windings is dominated by inductance, as one normally expects with a transformer. But the analysis handles the whole range of cases. Hi John, Through these last comments, and those that go before, you have entirely missed the boat of both the dynamics involved (this is not a magnetic circuit being described, and there are NO magnetic lines broken in a typical circuit in a balanced configuration), and the topology. Specifically to this last, you still do not seem to comprehend that a coax has three conductors and is a six terminal device. I appreciate you taking the time and effort to try to straighten me out on this, but if there is no magnetic lines broken (whatever that means) why use a magnetic core? Why wouldn't disks of carbon work just as well. They are certainly resistive. |
what a 1:1 choke balum used for
John Popelish wrote:
. . . I appreciate you taking the time and effort to try to straighten me out on this, but if there is no magnetic lines broken (whatever that means) why use a magnetic core? Why wouldn't disks of carbon work just as well. They are certainly resistive. But resistive impedance isn't the only characteristic of ferrite. Disks of carbon won't work because they have a relative permeability of one. Fair-Rite type 73 ferrite has a Q of 1 (R = X) at about 3 MHz, and is essentially resistive above that; it's a "low frequency" ferrite. But its relative permeability is 700 at 10 MHz and 70 at 100 MHz. (Note that the permeability is a complex quantity, and that the permeability is mostly imaginary, hence the impedance resistive, at the higher frequencies.) Carbon has a relative permeability of one at all frequencies. The impedance of a type 73 ferrite core picked at random from the Fair-Rite data shows an impedance of 23 ohms at 3 MHz, 37 at 10, 51 at 100, and 49 at 200 MHz. Try making a carbon disk that'll give you that impedance. And if you make your baluns with multiple turns on a single core as I do, you'll have much poorer coupling between turns on a carbon core, than on ferrite. You'll learn a lot by reading the information in the Fair-Rite catalog, available at their web site. Good, professionally written information on EMI suppression is useful also. But I don't recommend looking to amateur publications and web sites for information on ferrites -- too many people share the same misconceptions you do, and pass them along without really understanding how transformers work and the properties of ferrites. Actually, a large number of engineers share those misconceptions, too. It's often one of the first things I have to explain to the engineers in my consulting work. Roy Lewallen, W7EL |
what a 1:1 choke balum used for
On Wed, 29 Mar 2006 15:36:08 -0500, John Popelish
wrote: I appreciate you taking the time and effort to try to straighten me out on this, but if there is no magnetic lines broken (whatever that means) why use a magnetic core? Why wouldn't disks of carbon work just as well. They are certainly resistive. Hi John, Breaking magnetic lines (flux) is a commonplace of fields, motors, and generators. A single wire that passes through a bead, torus, or core will build a magnetic field concentrated within that structure when the circuit is completed outside of it. The flux lines of half the loop will penetrate the core to reach the other half of the loop. The core breaks the magnetic line of flux. The dissymmetry of penetration builds a magnetic field in the core. However, when the complete current loop is within the same structure, the flux lines do not fulfill that same function. The flux lines that do emerge from the tightly bound wires can be said to penetrate the torus, but here the symmetry creates bucking fields, the net effect is as though there was no core at all (except to add capacitance). Both models attempt to stimulate a current within the toroid, the common mode of the single wire model above is lossy, the differential mode of the twin line model that followed sees nothing. Superpose these two for the coaxial solution. To put this to a test. Load up your rig, through a SWR meter to a dummy load using two short connection wires (this will undoubtedly require adapters and such to break out both paths). You should note a 1:1 indication. Place two #75 beads on ONE wire. You should note a 2:1 indication. You have just inserted 40 to 60 Ohms of additional resistance into the circuit. Now, move the same two beads to encompass BOTH wires. This should return the SWR meter to a 1:1 indication. 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
rocky wrote:
To sort of sum things up, then what should I use for a choke balun on 75 meters, 77, 73 or 43 mix? More the better? I read the W2DU article and he used 73, but I thought 77 may be better? If you are going to have to go out and buy the cores, type 43 (and its competitors) is way more common and cheap than any of the others. It is also readily available in long form toroids called shield beads. For instance, Digikey sells the Steward version of type 43 (called type 28) beads part number 28B1122-100, with a 13.7mm hole and 28.6mm long. This part produces about 60 ohms per bead at 4 MHz and costs $20 for 10 pieces. http://www.steward.com/ What diameter coax do you want to use a choke BaLun on? Generally the smaller hole size, the more impedance you get out of a given length core. |
what a 1:1 choke balum used for
Richard Clark wrote:
(snip) #64 material is going to offer about 3 Ohms per bead; #43 material is going to offer about 8 Ohms per bead; #73 & 77 material is going to offer about 18 Ohms per bead; #75 material is going to show offer 28 Ohms per bead. (snip) What dimension cores produce these impedances at 75 meters? |
what a 1:1 choke balum used for
Roy Lewallen wrote:
Broadband transformers, which can operate well over several decades of frequency, commonly use ferrite cores which are essentially resistive over most of the operating frequency range. The sign of the impedance is unimportant to the transformer's operation; all that's necessary is that its magnitude be adequately high over the operating range (and of course that the core's permeability be adequately high). The wide band high impedance requirement is virtually impossible to meet with an inductive core whose impedance is approximately proportional to frequency, but easily done with cores whose impedance is essentially resistive. As long as the impedance is high enough, what is the need for it to be constant (or even nearly so) over a useful frequency range? |
what a 1:1 choke balum used for
On Wed, 29 Mar 2006 17:30:54 -0500, John Popelish
wrote: Richard Clark wrote: (snip) #64 material is going to offer about 3 Ohms per bead; #43 material is going to offer about 8 Ohms per bead; #73 & 77 material is going to offer about 18 Ohms per bead; #75 material is going to show offer 28 Ohms per bead. (snip) What dimension cores produce these impedances at 75 meters? Hi John, It is called a 101 sized bead: .138" OD .051" ID .128" high 73's Richard Clark, KB7QHC |
what a 1:1 choke balum used for
Richard Clark wrote:
Breaking magnetic lines (flux) is a commonplace ... If magnetic lines can be broken, doesn't that imply the existence of magnetic monopoles which have never been found to exist in reality? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
what a 1:1 choke balum used for
John Popelish wrote:
You'll learn a lot by reading the information in the Fair-Rite catalog, available at their web site. I have a hard copy right beside me, and refer to it often. I also have a fold-up brochure from Amidon dated March 1991 and titled: "Iron-Powder and Ferrite Coil Forms". -- 73, Cecil http://www.qsl.net/w5dxp |
what a 1:1 choke balum used for
Roy Lewallen wrote:
John Popelish wrote: . . . I appreciate you taking the time and effort to try to straighten me out on this, but if there is no magnetic lines broken (whatever that means) why use a magnetic core? Why wouldn't disks of carbon work just as well. They are certainly resistive. But resistive impedance isn't the only characteristic of ferrite. Disks of carbon won't work because they have a relative permeability of one. I know that. I wanted to see if Richard does. (snip) You'll learn a lot by reading the information in the Fair-Rite catalog, available at their web site. (snip) I have a hard copy right beside me, and refer to it often. |
what a 1:1 choke balum used for
Richard Clark wrote:
Hi John, Breaking magnetic lines (flux) is a commonplace of fields, motors, and generators. A single wire that passes through a bead, torus, or core will build a magnetic field concentrated within that structure when the circuit is completed outside of it. The flux lines of half the loop will penetrate the core to reach the other half of the loop. The core breaks the magnetic line of flux. The dissymmetry of penetration builds a magnetic field in the core. I cannot picture what you are saying. I guess I need a picture. The way I understand flux, is that, any current has flux wrapped around it. Putting a core material around the current allows the flux to increase in magnitude in proportion to the permeability of the material. However, when the complete current loop is within the same structure, the flux lines do not fulfill that same function. The simplest way to say that is that two equal currents going in opposite directions have magnetic fields that cancel well outside the pair of conductors. It doesn't make a lot of difference if the two currents are coaxial or side by side, as long as the flux path surrounds both of them. The flux lines that do emerge from the tightly bound wires can be said to penetrate the torus, but here the symmetry creates bucking fields, the net effect is as though there was no core at all (except to add capacitance). Since the magnetic fields from the two currents cancel (at sufficient distance), there is no flux to enter a surrounding core. The only way bucking takes place is if the two currents are side by side. Then there is some flux leakage near the two current paths, but the fields these create buck each other in the two halves of the core, so there is only local flux fringing into and back out of the core. Both models attempt to stimulate a current within the toroid, the common mode of the single wire model above is lossy, the differential mode of the twin line model that followed sees nothing. Superpose these two for the coaxial solution. As I understand common mode current, it is the net imbalance between the current through the center conductor and the current through the shield. To put this to a test. Load up your rig, through a SWR meter to a dummy load using two short connection wires (this will undoubtedly require adapters and such to break out both paths). You should note a 1:1 indication. Place two #75 beads on ONE wire. You should note a 2:1 indication. You have just inserted 40 to 60 Ohms of additional resistance into the circuit. Now, move the same two beads to encompass BOTH wires. This should return the SWR meter to a 1:1 indication. Yes, obvious to the casual observer. You can string beads all along a coax, and if it had no common mode current in it, this will make absolutely no difference in how the coax acts. |
what a 1:1 choke balum used for
Richard Clark wrote:
On Wed, 29 Mar 2006 17:30:54 -0500, John Popelish wrote: Richard Clark wrote: (snip) #64 material is going to offer about 3 Ohms per bead; #43 material is going to offer about 8 Ohms per bead; #73 & 77 material is going to offer about 18 Ohms per bead; #75 material is going to show offer 28 Ohms per bead. (snip) What dimension cores produce these impedances at 75 meters? Hi John, It is called a 101 sized bead: .138" OD .051" ID .128" high Are these what you recommend as coax choke balun beads? That is some fine coax. |
what a 1:1 choke balum used for
John Popelish wrote: rocky wrote: To sort of sum things up, then what should I use for a choke balun on 75 meters, 77, 73 or 43 mix? More the better? I read the W2DU article and he used 73, but I thought 77 may be better? If you are going to have to go out and buy the cores, type 43 (and its competitors) is way more common and cheap than any of the others. It is also readily available in long form toroids called shield beads. You are going to get into trouble with the W2DU balun at high power levels or with high commonn mode voltages across the balun. Each bead suggested is only good for about 1/2 watt dissipation in open air during long duty cycle. Also, a string of beads is a terribly inefficient use of ferrite materials. If you double the expense of the balun by doubling the number of beads, you only double the common mode impedance. If you use a less resistive material with lower loss tangent and multiple turns through the core, you can greatly increase power capacity and choking impedance with much less increase in cost. 73 or 75 material beads are great in 50 ohm systems at modest power on higher frequencies when the common mode excitation is low, but I'd stay away from that method at kilowatt power levels especially if common mode exciting the shield is high in level or frequency is low. For high stress applications a string of beads is terribly inefficient. 73 Tom |
what a 1:1 choke balum used for
John Popelish wrote:
Roy Lewallen wrote: Broadband transformers, which can operate well over several decades of frequency, commonly use ferrite cores which are essentially resistive over most of the operating frequency range. The sign of the impedance is unimportant to the transformer's operation; all that's necessary is that its magnitude be adequately high over the operating range (and of course that the core's permeability be adequately high). The wide band high impedance requirement is virtually impossible to meet with an inductive core whose impedance is approximately proportional to frequency, but easily done with cores whose impedance is essentially resistive. As long as the impedance is high enough, what is the need for it to be constant (or even nearly so) over a useful frequency range? None. Roy Lewallen, W7EL |
what a 1:1 choke balum used for
John Popelish wrote:
. . . As I understand common mode current, it is the net imbalance between the current through the center conductor and the current through the shield. If you consider the sum of the physically separate currents on the inside and outside of the shield to be the current "through the shield", that's correct. And it's equal to the current on the outside of the shield. . . . Roy Lewallen, W7EL |
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