Toroid Balun Cores
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I'm refurbishing an old antenna here and the toroid in the matching balun is
cracked in several places. Will that affect the toroid performance? 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Amateur Radio Operator N5GE
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Tom,
Are the cracks all the way through? If so, just as is I would think there would be an effect. Assuming little material is missing, I think you probably could carefully glue it back together, trying to get things as tight as possible. If the cracks don't separate it into pieces, I might try using super glue in the cracks to keep it together. Perhaps a more important question is why did it crack, and what can you do to prevent further cracking. If there was no obvious physical stress that caused the cracks, it sounds like it could be defective material in the first place and you might be better off replacing it if possible. 73 - Mike WA8BXN -------Original Message------- From: [hidden email] Date: 10/15/2011 8:30:31 PM To: Elecraft Subject: [Elecraft] Toroid Balun Cores I'm refurbishing an old antenna here and the toroid in the matching balun is Cracked in several places. Will that affect the toroid performance? ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by N5GE
Thanks to all that answered. I guessed it was toast. It's an old (1998 vintage) Cushcraft X7. I understand that the older ones had problems with the balun's, which is why probably why it quit working properly. 73, Tom Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member On Sat, 15 Oct 2011 19:29:57 -0500, [hidden email] wrote: >I'm refurbishing an old antenna here and the toroid in the matching balun is >cracked in several places. Will that affect the toroid performance? > >73, >Tom >Amateur Radio Operator N5GE >ARRL Lifetime Member >QCWA Lifetime Member > > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[hidden email] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Amateur Radio Operator N5GE
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In reply to this post by N5GE
On 10/15/2011 5:29 PM, [hidden email] wrote:
> I'm refurbishing an old antenna here and the toroid in the matching balun is > cracked in several places. Will that affect the toroid performance? Yep. It's toast. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by N5GE
On 10/15/2011 8:14 PM, Ron D'Eau Claire wrote:
> Back in the dark ages we had air core baluns. They were HUGE - an HF balun > might take up a couple of cubic feet of space - but they were impervious to > such failures since air doesn't saturate or crack, Hi! They also didn't do much except make us feel better. Ferrite core chokes actually DO something useful. The cracked balun was poorly designed, so it overheated. That's a DESIGN mistake, not a "defect" of ferrite cores. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Ron D'Eau Claire wrote:
>> >>They also didn't do much except make us feel better. Ferrite core chokes >>actually DO something useful. The cracked balun was poorly designed, so >>it overheated. That's a DESIGN mistake, not a "defect" of ferrite cores. >> >>73, Jim K9YC >> >Why would you think that? Properly designed, an air core balun and a >ferrite core balun are electrically identical. > That simply isn't true. Air-cored chokes are reactive in impedance, narrowband and easily detuned. A properly designed ferrite core choke is predominantly resistive and broadband, which makes it a much more dependable solution. Steve Hunt G3TXQ has measured a wide range of different chokes and plotted the results on a graphic that shows this point very clearly. <http://www.karinya.net/g3txq/chokes/> In Steve's graphic, an effective choke needs the largest possible bandwidth of dark green, preferably with the black underline denoting predominantly resistive impedance. This can only be achieved with the help of ferrite - and even then, only with the right ferrite core and the right kind of winding. Air-cored chokes are shown to be relatively ineffective, narrowband devices... and then there's worse. Steve has also shown that the series reactances of the feedline and the wrong kind of air-cored choke can sometimes cancel, leading to a higher level of common mode current than before. This cannot happen with a ferrite choke that is predominantly resistive. For further information read Steve's page followed perhaps by my own article, at: <http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#1005> That in turn will lead you on to K9YC's much longer papers. Steve, Jim and I have different styles of presentation but we're absolutely agreed on the one key point: an air-core choke and a ferrite-core choke are very different indeed. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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An interesting discussion...much is usually made of the "self-shielding"
property of ferrite toroids, and we see this in practice in interstage transformers as well as in "baluns [sic]". (I am talking here about the "balun" type also called a "choke balun.") However, it is also a fact that the magnetic field outside a cylindrical solenoid tends to zero as the solenoid tends to "infinite" length. So, for example a choke balun wound on a cylindrical form rather than as a clump of scramble-wound turns is also more or less self-shielding. Parenthetically, it is this self-shielding nature of solenoids that plays an important role in experimental verification of the Ahranov-Bohm effect (see recent QEX article by Robert Zimmerman and Feynman Lectures Vol. II Chapter 15, sections 15.4 and 15.5). I agree with the contributor(s) who said that the cracked toroid is basically junk. It has lost its utility because the magnetic circuit is broken at the crack. It is unlikely that superglue will restore it. John Ragle -- W1ZI ===== On 10/16/2011 4:41 PM, Ian White GM3SEK wrote: > Ron D'Eau Claire wrote: >>> They also didn't do much except make us feel better. Ferrite core chokes >>> actually DO something useful. The cracked balun was poorly designed, so >>> it overheated. That's a DESIGN mistake, not a "defect" of ferrite cores. >>> >>> 73, Jim K9YC >>> >> Why would you think that? Properly designed, an air core balun and a >> ferrite core balun are electrically identical. >> > That simply isn't true. Air-cored chokes are reactive in impedance, > narrowband and easily detuned. A properly designed ferrite core choke is > predominantly resistive and broadband, which makes it a much more > dependable solution. > > Steve Hunt G3TXQ has measured a wide range of different chokes and > plotted the results on a graphic that shows this point very clearly. > > <http://www.karinya.net/g3txq/chokes/> > > In Steve's graphic, an effective choke needs the largest possible > bandwidth of dark green, preferably with the black underline denoting > predominantly resistive impedance. This can only be achieved with the > help of ferrite - and even then, only with the right ferrite core and > the right kind of winding. > > Air-cored chokes are shown to be relatively ineffective, narrowband > devices... and then there's worse. Steve has also shown that the series > reactances of the feedline and the wrong kind of air-cored choke can > sometimes cancel, leading to a higher level of common mode current than > before. This cannot happen with a ferrite choke that is predominantly > resistive. > > For further information read Steve's page followed perhaps by my own > article, at: > > <http://www.ifwtech.co.uk/g3sek/in-prac/index.htm#1005> > > That in turn will lead you on to K9YC's much longer papers. Steve, Jim > and I have different styles of presentation but we're absolutely agreed > on the one key point: an air-core choke and a ferrite-core choke are > very different indeed. > > > -- Sent from my lovely old Dell XPS 420 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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OK, now I am confused (a normal state of affairs around here) If a "cracked" toroid core is useless, then how do the "split bead" clamp-on cores manage to work? Isn't the "split" equivalent to as great big lengthwise crack? I also seem to remember broken ring cores working again when glued together. After all, isn't a ferrite core itself manufactured from ferrite powder that has been "glued together" by a binding material? Yes, the particles are pressed very close to one another,but they are still individual particles, are they not? - Jim, KL7CC John Ragle wrote: > <snip> > > I agree with the contributor(s) who said that the cracked toroid is > basically junk. It has lost its utility because the magnetic circuit is > broken at the crack. It is unlikely that superglue will restore it. > > John Ragle -- W1ZI > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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First, even a very thin gap may significantly reduce the core
permeability. A high quality split core will have its mating surfaces lapped flat. Second, if the core cracked because of excessive heat, it's likely the ferrite material incurred irreversible damage. Jack K8ZOA On 10/16/2011 5:58 PM, Jim Wiley wrote: > > OK, now I am confused (a normal state of affairs around here) > > > If a "cracked" toroid core is useless, then how do the "split bead" > clamp-on cores manage to work? Isn't the "split" equivalent to as great > big lengthwise crack? > > > I also seem to remember broken ring cores working again when glued > together. > > > After all, isn't a ferrite core itself manufactured from ferrite powder > that has been "glued together" by a binding material? Yes, the > particles are pressed very close to one another,but they are still > individual particles, are they not? > > > - Jim, KL7CC > > > > John Ragle wrote: >> <snip> >> >> I agree with the contributor(s) who said that the cracked toroid is >> basically junk. It has lost its utility because the magnetic circuit is >> broken at the crack. It is unlikely that superglue will restore it. >> >> John Ragle -- W1ZI >> >> >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Some confusion results from the fact that there are two different materials used in
toroids (etc.): Ferrite and powdered iron. Powdered iron cores are composed of tiny particles which are insulated from one another...so if they break you can glue them back together and they will work fine. Ferrite is a ceramic material, and if you glue a broken piece of ferrite back together you are introducing an insulating gap which breaks the magnetic circuit. Powdered iron is a bunch of little magnets separated by gaps already. Baluns seem to be made out of ferrite. On 10/16/2011 3:13 PM, Jack Smith wrote: > First, even a very thin gap may significantly reduce the core > permeability. A high quality split core will have its mating surfaces > lapped flat. > > Second, if the core cracked because of excessive heat, it's likely the > ferrite material incurred irreversible damage. > > Jack K8ZOA > > > On 10/16/2011 5:58 PM, Jim Wiley wrote: >> >> OK, now I am confused (a normal state of affairs around here) >> >> >> If a "cracked" toroid core is useless, then how do the "split bead" >> clamp-on cores manage to work? Isn't the "split" equivalent to as great >> big lengthwise crack? >> >> >> I also seem to remember broken ring cores working again when glued >> together. >> >> >> After all, isn't a ferrite core itself manufactured from ferrite powder >> that has been "glued together" by a binding material? Yes, the >> particles are pressed very close to one another,but they are still >> individual particles, are they not? >> >> >> - Jim, KL7CC >> >> >> >> John Ragle wrote: >>> <snip> >>> >>> I agree with the contributor(s) who said that the cracked toroid is >>> basically junk. It has lost its utility because the magnetic circuit is >>> broken at the crack. It is unlikely that superglue will restore it. >>> >>> John Ragle -- W1ZI >>> >>> -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Jim Wiley-2
Jim...
I think the snap-ons are designed to be lossy devices. They are designed to be a convenient shape for wires, cords, cables, etc. and to provide loss for fields that fringe out of those cables. Tiny air gaps are not particularly important for this function. Ferrite donuts used as transformer cores are for transferring magnetic flux from primary to secondary without leakage. In a real balun, the action is as a transformer...remember those plug-in coils with "links" on them that Millen et al. used to make, back when...? Those were air-core transformers (and not very efficient...). The core in the balun on your beam was probably a transformer core. Again, 'way back when, when transformers for tube "B+" & filament voltages were normal parts of power supplies, the windings were on interleaved, laminated "E"-shaped core material. In those, working at 60 Hz, a tiny air gap could be tolerated, even though its effect was somewhat like a "magnetic" resistor in the flux path. One does not see these as much any more, but I can remember taking them apart to harvest the wire inside...and being left with dozens of the laminations... John Ragle -- W1ZI ===== On 10/16/2011 5:58 PM, Jim Wiley wrote: > > OK, now I am confused (a normal state of affairs around here) > > > If a "cracked" toroid core is useless, then how do the "split bead" > clamp-on cores manage to work? Isn't the "split" equivalent to as great > big lengthwise crack? > > > I also seem to remember broken ring cores working again when glued > together. > > > After all, isn't a ferrite core itself manufactured from ferrite powder > that has been "glued together" by a binding material? Yes, the > particles are pressed very close to one another,but they are still > individual particles, are they not? > > > - Jim, KL7CC > > > > John Ragle wrote: >> <snip> >> >> I agree with the contributor(s) who said that the cracked toroid is >> basically junk. It has lost its utility because the magnetic circuit is >> broken at the crack. It is unlikely that superglue will restore it. >> >> John Ragle -- W1ZI >> >> >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > > > -- Sent from my lovely old Dell XPS 420 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Vic Rosenthal
On 10/16/2011 4:29 PM, Vic K2VCO wrote:
> two different materials used in > toroids (etc.): Ferrite and powdered iron. AND each generic type -- ferrites and powdered iron -- have many variations that are VERY different from each other. The ferrite types are different as a result of their chemical MIX, and every MIX is designed for a different use -- that is, suppression over one range of frequencies and/or inductance in a different range of frequencies. See the RFI tutorial on my website about these matters. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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