Hum Coupling
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G'day,
By coincidence I opened up our stereo amp to have a go at lubricating a noisy volume pot. I noticed that the torroidal mains transformer was of shielded construction. Maybe this is the answer to the PSU hum coupling problem. A 20A psu in a double height EC, speaker etc as has already been suggested. Regards, Mike VP8NO _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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This belongs in the For What Its Worth file:
I cannot help but note that the venerable Kenwood TS-930S and TS-940S rigs had their big hunk of a power transformer mounted right next to the PLL section - and no hum problems were apparent, and it was NOT a toroidal type transformer, just a standard E+I section type, with no outer cover - you could see the laminations and windings. Yes, the PLL assemblies were inside shielded compartments, but there did not appear to be anything special about them - specifically, they were not "Mu Metal", although they were steel. However, the radio would operate just fine when the shield covers were open - as during testing and alignment, so the shielding or lack thereof (in the Kenwoods) was not germane to that sort of problem. What was different about their design that made it "hum proof" - at least from fields induced by the mains transformer? So, maybe the problem could be worth another look, as in maybe there is another way to solve it? Could something be done to the K2 itself to make it immune to this problem? This needs someone who is a better engineer than me to come up with an answer- I am just a lowly self-taught fumbler. 73, - Jim, KL7CC Michael Harris wrote: >G'day, > >By coincidence I opened up our stereo amp to have a go at lubricating a >noisy volume pot. I noticed that the torroidal mains transformer was of >shielded construction. > >Maybe this is the answer to the PSU hum coupling problem. A 20A psu in a >double height EC, speaker etc as has already been suggested. > >Regards, > >Mike VP8NO > >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Jim, KL7CC wrote:
"So, maybe the problem [hum getting into the K2's PLL] could be worth another look, as in maybe there is another way to solve it? Could something be done to the K2 itself to make it immune to this problem?" ========== Hum coupling from the K2's power supply xfmr is not much of a problem because separation of a couple of feet eliminates it. Hum coupling from a linear amp's hypersil HV xfmr is another story, however. Six feet is not sufficient distance from my Alpha 76CA. Ditto when my K2 was tried more than six feet from my friend's Alpha 99. Thirty feet separation does clear up the problem, but that is unacceptable. I am a QRO operator who chases DX and works the contests, so I cannot use my K2 for this purpose because of the trashy signal it puts out when used with an amplifier. Elecraft is aware of the problem and was going to investigate further into it, but that was perhaps a year ago. They were going to look into the possibility of fabricating a mu metal shield, but I have heard nothing back from them since. If no fix becomes evident soon, I'm afraid my K2/100 will be up for sale. 73, de Earl, K6SE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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As is probably typical of magnetic coupling, when I run my K2 with a
Henry 2K desk model set at right angles to the operating desk within arms reach I don't appear to have the problem. At least no one complained during my 1700+ qsos during CQP. In fact I had many compliments on the audio quality. Or I'm just lucky. I'll take it. Ken K6MR Earl W Cunningham wrote: >Jim, KL7CC wrote: > >"So, maybe the problem [hum getting into the K2's PLL] could be worth >another look, as in maybe there is another way to solve it? Could >something be done to the K2 itself to make it immune to this problem?" >========== >Hum coupling from the K2's power supply xfmr is not much of a problem >because separation of a couple of feet eliminates it. > >Hum coupling from a linear amp's hypersil HV xfmr is another story, >however. Six feet is not sufficient distance from my Alpha 76CA. Ditto >when my K2 was tried more than six feet from my friend's Alpha 99. >Thirty feet separation does clear up the problem, but that is >unacceptable. > >I am a QRO operator who chases DX and works the contests, so I cannot use >my K2 for this purpose because of the trashy signal it puts out when used >with an amplifier. > >Elecraft is aware of the problem and was going to investigate further >into it, but that was perhaps a year ago. They were going to look into >the possibility of fabricating a mu metal shield, but I have heard >nothing back from them since. If no fix becomes evident soon, I'm afraid >my K2/100 will be up for sale. > >73, de Earl, K6SE >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com > > > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
In a message dated 11/1/04 8:36:41 PM Eastern Standard Time,
[hidden email] writes: > I cannot help but note that the venerable Kenwood TS-930S and TS-940S > rigs had their big hunk of a power transformer mounted right next to the > PLL section - and no hum problems were apparent, and it was NOT a > toroidal type transformer, just a standard E+I section type, with no > outer cover - you could see the laminations and windings. > > > Yes, the PLL assemblies were inside shielded compartments, but there did > not appear to be anything special about them - specifically, they were > not "Mu Metal", although they were steel. There's the answer. Steel is ferromagnetic, aluminum isn't. Steel isn't as good a shield as MuMetal, but it does the job. I suspect that a K2 built with a steel cabinet would be much more magnetic-field immune than the stock aluminum case. It would also weigh a lot more, but that may not be a problem for home use. However, the radio would > > operate just fine when the shield covers were open - as during testing > and alignment, so the shielding or lack thereof (in the Kenwoods) was > not germane to that sort of problem. Was the entire shield removed, or just the covers? I suspect a lot of the shield wss still in place. What was different about their > > design that made it "hum proof" - at least from fields induced by the > mains transformer? > > The steel shield is a big factor. Another is that they may not have used iron-core coils in the PLL, or used a different type of iron. Yet another is the frequency range of the PLL. The prime suspect, IMHO, in the K2 hum pickup is the PLL coils with their iron cores. 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Interesting - I had complaint on air recently of having a wide CW carrier
when using a tube linear about two feet from the K2/100. Fraser G4BJM >From: Earl W Cunningham <[hidden email]> >To: [hidden email], [hidden email],[hidden email] >Subject: Re: [Elecraft] Hum Coupling >Date: Mon, 1 Nov 2004 19:49:07 -0800 > >Jim, KL7CC wrote: > >"So, maybe the problem [hum getting into the K2's PLL] could be worth >another look, as in maybe there is another way to solve it? Could >something be done to the K2 itself to make it immune to this problem?" >========== >Hum coupling from the K2's power supply xfmr is not much of a problem >because separation of a couple of feet eliminates it. > >Hum coupling from a linear amp's hypersil HV xfmr is another story, >however. Six feet is not sufficient distance from my Alpha 76CA. Ditto >when my K2 was tried more than six feet from my friend's Alpha 99. >Thirty feet separation does clear up the problem, but that is >unacceptable. > >I am a QRO operator who chases DX and works the contests, so I cannot use >my K2 for this purpose because of the trashy signal it puts out when used >with an amplifier. > >Elecraft is aware of the problem and was going to investigate further >into it, but that was perhaps a year ago. They were going to look into >the possibility of fabricating a mu metal shield, but I have heard >nothing back from them since. If no fix becomes evident soon, I'm afraid >my K2/100 will be up for sale. > >73, de Earl, K6SE >_______________________________________________ >Elecraft mailing list >Post to: [hidden email] >You must be a subscriber to post to the list. >Subscriber Info (Addr. Change, sub, unsub etc.): >http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/subscribers.htm >Elecraft web page: http://www.elecraft.com _________________________________________________________________ Stay in touch with absent friends - get MSN Messenger http://www.msn.co.uk/messenger _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Fraser Robertson wrote:
> Interesting - I had complaint on air recently of having a wide CW > carrier when using a tube linear about two feet from the K2/100. I do NOT have the problem (and I've had people listen carefully for it) with an Alpha 86 at full power located 4 feet from the K2. For what it's worth the front panel of the Alpha is perpendicular to the front panel of the K2. The Alpha has an enormous Hypersil transformer, as Earl mentions. I did have the problem with my HAM/2 antenna rotor control box closer than about two feet from the K2. -- 73, Vic, K2VCO Fresno CA http://www.qsl.net/k2vco _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Fraser, G4BJM wrote:
"Interesting - I had complaint on air recently of having a wide CW carrier when using a tube linear about two feet from the K2/100." ========== Exactly the problem. Rather than hum, it sounds like noise on the sidebands of the signal -- becoming less broad as the distance between the K2 and the amp increases. This is easily heard when you monitor your transmitted signal on another receiver. The K2/100 is absolutely clean barefoot. Perhaps the field from a hypersil xfmr is greater than a "normal" xfmr. Both Alphas I have tested my K2 on, at home and at a friend's QTH) have hypersil HV xfmrs. I even removed the KPA100 and ran my 10-watt K2 into the amp with the same noisy sidebands occurring on its CW and SSB output. There IS a problem! 73, de Earl, K6SE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Earl W Cunningham
Earl,
Contact the companies that sell mu metal products and you can get a mu metal foil or tape that should take care of the problem. That and some distance from the offending linear should help. Maybe even doing the MU Metal shield around the power transformer and choke of the linear would be enough. -Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Thanks for the mu metal info, Stuart.
If Eric and Wayne don't come out with a mod for it, I'll try that. 73, de Earl, K6SE _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
I have been following the "Hum Coupling" thread, and would like to comment,
from the viewpoint of an engineer who has done a lot of interference reduction. My guess is that magnetic fields from power transformers are either 1) being picked up by L30, or 2) that the magnetic fields are going through the cores of L30 and/or T5, and modulating the effective permeabilities of these cores. This will cause a modulation of inductance, and thus a modulation of the VFO frequency. There are two general solutions: First, one can make the cores less susceptible to permeability modulation by using lower permeability cores (although that would require more wire turns, and perhaps physically larger inductors to have the same inductance/coupling. Second, one can use shielding that is effective for low frequency magnetic fields, at the source, at the VFO, or both. That means, of course, a ferromagnetic material. Equipment that uses aluminum case construction offers little to no protection against magnetic fields below around 10MHz, and it isn't great until you get above 30MHz. Regarding shielding at the VFO, mu-metal is great stuff, but it is hard to apply. If you bend or form it at all, you will have to anneal it to get back its amazing high permeability and shielding effectiveness. Most people wind up using mild steel. For a given thickness it isn't as effective as mu-metal. However, it can be formed without the necessity of annealing. And, you can simply use more, if you like. To work best, the magnetic shield should completely surround the susceptible parts. Sometimes, you don't need the absolute best solution to make things good enough. For example, I have sometimes reduced interference enough by wrapping a few turns of hypersil tape around the outside of a toroid (this is the same thin metal tape that tape-wound transformer cores are made of). Also, one could try somehow putting a sheet of mild steel between the interference source and its target. Regarding shielding the interference source (a large power transformer), that is a lot harder. Mu-metal is ineffective because the strong magnetic fields near a high power transformer will saturate the mu-metal (it saturates easily), rendering it useless. Again, our friend, mild steel, can come to the rescue. A steel enclosure helps. For an E-I core transformer, steel end bells help. Toroidal power transformers have much lower external fields, but they are not zero. Enclosing the transformer in a steel box can help, provided that the transformer can run cool enough. [Whatever you do, never run a bolt through the core of a toroidal transformer if there is any possibility that the two ends can be connected together (such as by both touching the same metal box). It would be a shorted turn!] Of course, if the whole equipment using the big power transformer is in a steel box, that helps. Here's a possibility for experimenting with K2 susceptibility: Try using one of those bulk tape erasers near it. They put out huge 60Hz fields. [Just don't get it near your credit/bank cards!] Since I don't have a K2, I can't try this myself, but I would be happy to correspond with anyone trying to solve these problems. I am considering getting a K2, and joined this reflector to learn more about it. 73, Allen Walker _________________________________________________________________ FREE pop-up blocking with the new MSN Toolbar – get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Hello Allen,
>My guess is that magnetic fields from power transformers are either 1) being >picked up by L30, or 2) that the magnetic fields are going through the cores >of L30 and/or T5, and modulating the effective permeabilities of these >cores. This will cause a modulation of inductance, and thus a modulation of >the VFO frequency. The magnetic field is picked up by L30. >To work best, the magnetic shield should completely surround the susceptible parts. Putting the shield on only one side seems to make things worse. >Here's a possibility for experimenting with K2 susceptibility: Try using one >of those bulk tape erasers near it. They put out huge 60Hz fields. [Just >don't get it near your credit/bank cards!] Of course, keep it away from the latching relays. I used a tape head demagnetizer. Placing the probe near the base of L30 causes a vast huge amount of FM. Don't try this unless you cut the current way down. Looking on the scope, FM modulation is at 60 Hz, not 120 Hz, so we're not modulating the permeability, we seem to be inducing a 60 Hz voltage onto L30/T5 which is modulating the varacters. What I don't understand is this: I figure L30 has perhaps 14 turns, and 2.3 ohms winding resistance. I figure that the effective aperture is 1 cm squared. I figure that the winding resistance of T5 is 0.05 ohms, so a 1 gauss vertical 60 Hz field will induce 37 micro volts on T5. That should cause 0.3 Hz FM modulation on 80 meters. No one should notice that? BTW, I calculated 2.3 ohms from the Q, sensitivity at T5 goes way up if L30 has less resistance. I know that the cup and core used in L30 will focus any external field through the winding, but I don't know how to calculate how much. It would be nice if someone could put an L30 (TOKO T1005Z 4.7 uH) into a Helholtz coil and get the numbers on it (uV/gauss at 60Hz, winding resistance). 73, Michael _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Mike Harris-9
Hi Michael,
Thanks for your comments. I think you are on to something. The only hope for lower magnetic field susceptibility for the K2 would be if either the VFO circuit were changed so as not to use an inductor for adjusting the quiescent resonance point of the VFO, or good magnetic shielding were used. One possibility would be to use a gapped pot core with slug tuning for L30, but it might be difficult to get sufficient adjustment range. Or, perhaps one could use some kind of shield for L30 alone. The standard sort of thing for low-level or precise RF circuits is to enclose them all in steel shielding, with steel partitions between circuit sections or stages (it's called "egg crating"). It's something Elecraft could keep in mind for a "K3." If I had a K2 in front of me, I think I would try to put some kind of shielding around L30. Here is the web site of one vendor of shielding materials: http://www.lessemf.com/mag-shld.html By the way, I would guess that the Q of that Toko T1005 coil is determined by not only DC resistive loss in the wire, but also skin effect loss and core loss (and circulating currents from distributed capacitance, etc., etc.). I suppose we will never know for sure, as RF work at some point gets very empirical -- we just have to try it out, and if it works we're on to solving the next problem. Best of luck, 73, Allen Walker >From: "Masleid, Michael A." <[hidden email]> >To: A Walker <[hidden email]> >CC: [hidden email] >Subject: RE: [Elecraft] Hum Coupling >Date: Wed, 03 Nov 2004 13:01:47 -0600 > >Hello Allen, > > >My guess is that magnetic fields from power transformers are either 1) >being > >picked up by L30, or 2) that the magnetic fields are going through the >cores > >of L30 and/or T5, and modulating the effective permeabilities of these > >cores. This will cause a modulation of inductance, and thus a modulation >of > >the VFO frequency. > >The magnetic field is picked up by L30. > > >To work best, the magnetic shield should completely surround the >susceptible parts. > >Putting the shield on only one side seems to make things worse. > > >Here's a possibility for experimenting with K2 susceptibility: Try using >one > >of those bulk tape erasers near it. They put out huge 60Hz fields. [Just > >don't get it near your credit/bank cards!] > >Of course, keep it away from the latching relays. > >I used a tape head demagnetizer. Placing the probe near the base of L30 >causes >a vast huge amount of FM. Don't try this unless you cut the current way >down. > >Looking on the scope, FM modulation is at 60 Hz, not 120 Hz, so we're not >modulating >the permeability, we seem to be inducing a 60 Hz voltage onto L30/T5 which >is >modulating the varacters. > >What I don't understand is this: I figure L30 has perhaps 14 turns, and >2.3 ohms >winding resistance. I figure that the effective aperture is 1 cm squared. >I figure >that the winding resistance of T5 is 0.05 ohms, so a 1 gauss vertical 60 Hz >field will >induce 37 micro volts on T5. That should cause 0.3 Hz FM modulation on 80 >meters. >No one should notice that? BTW, I calculated 2.3 ohms from the Q, >sensitivity at >T5 goes way up if L30 has less resistance. > >I know that the cup and core used in L30 will focus any external field >through the >winding, but I don't know how to calculate how much. > >It would be nice if someone could put an L30 (TOKO T1005Z 4.7 uH) into a >Helholtz >coil and get the numbers on it (uV/gauss at 60Hz, winding resistance). > >73, Michael _________________________________________________________________ Check out Election 2004 for up-to-date election news, plus voter tools and more! http://special.msn.com/msn/election2004.armx _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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I remembered this thread and when I was looking at the slashdot article
on RF shielding paint the other day, remembered that I had problems with my K2 and a flourescent "Ott" light, presumably from its transformer. I ordered some "Metglas" tape from these folks, and tried a few layers of it around the transformer, and near the K2, but there was no effect. I opened up the bottom of the K2 and noticed the greatest disturbance from the lamp transformer was around L31. That area also seemed to be the most sensitive to detuning when I put on and took off the cover (and my hand). So I put a few layers of the tape (insulated inside a poly) on top of L31 and there seemed to be a slight effect, but not enough to make me want to try to put it there. I may open the top and try L30. In better news, though, I found that moving the light from the left of the K2 to the right eliminated the modulation, at least on RX. Leigh. A Walker wrote: > Hi Michael, > > Thanks for your comments. I think you are on to something. > > The only hope for lower magnetic field susceptibility for the K2 would > be if either the VFO circuit were changed so as not to use an inductor > for adjusting the quiescent resonance point of the VFO, or good > magnetic shielding were used. One possibility would be to use a gapped > pot core with slug tuning for L30, but it might be difficult to get > sufficient adjustment range. Or, perhaps one could use some kind of > shield for L30 alone. The standard sort of thing for low-level or > precise RF circuits is to enclose them all in steel shielding, with > steel partitions between circuit sections or stages (it's called "egg > crating"). It's something Elecraft could keep in mind for a "K3." > > If I had a K2 in front of me, I think I would try to put some kind of > shielding around L30. Here is the web site of one vendor of shielding > materials: > > http://www.lessemf.com/mag-shld.html > > By the way, I would guess that the Q of that Toko T1005 coil is > determined by not only DC resistive loss in the wire, but also skin > effect loss and core loss (and circulating currents from distributed > capacitance, etc., etc.). I suppose we will never know for sure, as RF > work at some point gets very empirical -- we just have to try it out, > and if it works we're on to solving the next problem. > > Best of luck, > 73, Allen Walker > >> From: "Masleid, Michael A." <[hidden email]> >> To: A Walker <[hidden email]> >> CC: [hidden email] >> Subject: RE: [Elecraft] Hum Coupling >> Date: Wed, 03 Nov 2004 13:01:47 -0600 >> >> Hello Allen, >> >> >My guess is that magnetic fields from power transformers are either >> 1) being >> >picked up by L30, or 2) that the magnetic fields are going through >> the cores >> >of L30 and/or T5, and modulating the effective permeabilities of these >> >cores. This will cause a modulation of inductance, and thus a >> modulation of >> >the VFO frequency. >> >> The magnetic field is picked up by L30. >> >> >To work best, the magnetic shield should completely surround the >> susceptible parts. >> >> Putting the shield on only one side seems to make things worse. >> >> >Here's a possibility for experimenting with K2 susceptibility: Try >> using one >> >of those bulk tape erasers near it. They put out huge 60Hz fields. >> [Just >> >don't get it near your credit/bank cards!] >> >> Of course, keep it away from the latching relays. >> >> I used a tape head demagnetizer. Placing the probe near the base of >> L30 causes >> a vast huge amount of FM. Don't try this unless you cut the current >> way down. >> >> Looking on the scope, FM modulation is at 60 Hz, not 120 Hz, so we're >> not modulating >> the permeability, we seem to be inducing a 60 Hz voltage onto L30/T5 >> which is >> modulating the varacters. >> >> What I don't understand is this: I figure L30 has perhaps 14 turns, >> and 2.3 ohms >> winding resistance. I figure that the effective aperture is 1 cm >> squared. I figure >> that the winding resistance of T5 is 0.05 ohms, so a 1 gauss vertical >> 60 Hz field will >> induce 37 micro volts on T5. That should cause 0.3 Hz FM modulation >> on 80 meters. >> No one should notice that? BTW, I calculated 2.3 ohms from the Q, >> sensitivity at >> T5 goes way up if L30 has less resistance. >> >> I know that the cup and core used in L30 will focus any external >> field through the >> winding, but I don't know how to calculate how much. >> >> It would be nice if someone could put an L30 (TOKO T1005Z 4.7 uH) >> into a Helholtz >> coil and get the numbers on it (uV/gauss at 60Hz, winding resistance). >> >> 73, Michael > > > __________ _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Leigh, most of your coupling may be magnetic, if shielding did not reduce
the RFI. You might want to experiment with steel shim stock or even tinplate from cans. The easiest fix is distance: Moving the rig away from magnetic and electric field sources of transformers as you have found. GL, Stuart K5KVH |
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Thanks! The foil is supposed to have be very good for magnetic
shielding and so I thought I would try it, as it is small and light enough that it could be put inaide the rig if it works. I will report when I try it on L30. Leigh. On Mon, 3 Jan 2005 6:53 pm, Stuart Rohre wrote: > Leigh, most of your coupling may be magnetic, if shielding did not > reduce > the RFI. > > You might want to experiment with steel shim stock or even tinplate > from > cans. > > The easiest fix is distance: Moving the rig away from magnetic and > electric field sources of transformers as you have found. > GL, > Stuart > K5KVH > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Aluminum foil has very slight magnetic shielding, but there is commercial mu
metal foil that is very expensive but very good. Thin sheet metal is cheaper and more readily found. Check it with a magnet to see if it will work as magnetic shield. If magnet sticks it is steel or ferrous (shield ability) material. -Stuart K5KVH |
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Thank you! Yes, this is commercial Mu Metal shielding, but no the same
brand. The magnetic permeability is >1,000,000 and it can be bent. See the link to lessemf.com in the original message for purchase info. I got $5 worth. It is fun stuff. Leigh. On Tue, 4 Jan 2005 3:23 pm, Stuart Rohre wrote: > Aluminum foil has very slight magnetic shielding, but there is > commercial mu > metal foil that is very expensive but very good. > > Thin sheet metal is cheaper and more readily found. Check it with a > magnet > to see if it will work as magnetic shield. If magnet sticks it is > steel or > ferrous (shield ability) material. > -Stuart > K5KVH Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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