K3 External 2nd receiver with KXV3 and 6m pre-amp?
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On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote:
>Yes, I have several ferrite core 2.5 mH chokes here, including the >Hammond one you mention. There's a significant difference in high >frequency performance of the pi wound on ceramic form versus the smaller >pi-wound over ferrite and that's one of the things I'm hoping to >illustrate in the article. The RFI and Ferrite tutorial on my website includes clear explanations of the nature of ferrite materials from a circuit point of view. You may find it helpful in explaining why your very correct in your analysis. You are welcome to cite it as a reference. http://audiosystemsgroup.com/RFI-Ham.pdf However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 MHz. 73, Jim Brown K9YC _______________________________________________ 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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Jim:
Thank you for the reference. Indeed, the self-resonant frequency of the typical small (FT50 size) chokes I've wound are in the 5-10 MHz range, but at 100 MHz some (depending upon the core material) still show enough Z to be useful. For truly wideband 10 KHz - 100 MHz choke action, it's necessary to series two wound with different core material and turns, e.g., 35 turns on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on FairRite 43 material for > 50 MHz. You have to pay particular attention to the u' and u'' values of the ferrite material and how they change with frequency as this is a case where core loss at high frequencies can be good. Jack K8ZOA Jim Brown wrote: > On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote: > > >> Yes, I have several ferrite core 2.5 mH chokes here, including the >> Hammond one you mention. There's a significant difference in high >> frequency performance of the pi wound on ceramic form versus the smaller >> pi-wound over ferrite and that's one of the things I'm hoping to >> illustrate in the article. >> > > The RFI and Ferrite tutorial on my website includes clear explanations of > the nature of ferrite materials from a circuit point of view. You may find > it helpful in explaining why your very correct in your analysis. You are > welcome to cite it as a reference. > > http://audiosystemsgroup.com/RFI-Ham.pdf > > However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 > MHz. > > 73, > > Jim Brown K9YC > > > > _______________________________________________ > 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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When you wire two chokes of different value in series, you almost always
get a series-resonant "hole" in the attenuation somewhere between the parallel-resonant frequencies of the two chokes. It's not hard to see why that's true if you model each choke as an ideal inductor in parallel with a capacitor. So you need to design the combination so that the series-resonant frequency falls somewhere unimportant. Al N1AL On Thu, 2008-07-31 at 09:14, Jack Smith wrote: > Jim: > > Thank you for the reference. > > Indeed, the self-resonant frequency of the typical small (FT50 size) > chokes I've wound are in the 5-10 MHz range, but at 100 MHz some > (depending upon the core material) still show enough Z to be useful. > For truly wideband 10 KHz - 100 MHz choke action, it's necessary to > series two wound with different core material and turns, e.g., 35 turns > on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on > FairRite 43 material for > 50 MHz. > > You have to pay particular attention to the u' and u'' values of the > ferrite material and how they change with frequency as this is a case > where core loss at high frequencies can be good. > > Jack K8ZOA > > > Jim Brown wrote: > > On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote: > > > > > >> Yes, I have several ferrite core 2.5 mH chokes here, including the > >> Hammond one you mention. There's a significant difference in high > >> frequency performance of the pi wound on ceramic form versus the smaller > >> pi-wound over ferrite and that's one of the things I'm hoping to > >> illustrate in the article. > >> > > > > The RFI and Ferrite tutorial on my website includes clear explanations of > > the nature of ferrite materials from a circuit point of view. You may find > > it helpful in explaining why your very correct in your analysis. You are > > welcome to cite it as a reference. > > > > http://audiosystemsgroup.com/RFI-Ham.pdf > > > > However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 > > MHz. > > > > 73, > > > > Jim Brown K9YC > > > > > > > > _______________________________________________ > > 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 _______________________________________________ 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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Indeed such is the case, and it is quite pronounced with high Q inductors.
You may wish, however, to model and/or measure two series chokes when both are wound on lossy ferrite material. The response looks quite different. The resistance in parallel with the inductors radically modifies the response when the material causes the inductor Q to be < 1. I'll E-mail you some early measurements and a quick simulation plots. Jack K8ZOA Alan Bloom wrote: > When you wire two chokes of different value in series, you almost always > get a series-resonant "hole" in the attenuation somewhere between the > parallel-resonant frequencies of the two chokes. It's not hard to see > why that's true if you model each choke as an ideal inductor in parallel > with a capacitor. So you need to design the combination so that the > series-resonant frequency falls somewhere unimportant. > > Al N1AL > > > On Thu, 2008-07-31 at 09:14, Jack Smith wrote: > >> Jim: >> >> Thank you for the reference. >> >> Indeed, the self-resonant frequency of the typical small (FT50 size) >> chokes I've wound are in the 5-10 MHz range, but at 100 MHz some >> (depending upon the core material) still show enough Z to be useful. >> For truly wideband 10 KHz - 100 MHz choke action, it's necessary to >> series two wound with different core material and turns, e.g., 35 turns >> on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on >> FairRite 43 material for > 50 MHz. >> >> You have to pay particular attention to the u' and u'' values of the >> ferrite material and how they change with frequency as this is a case >> where core loss at high frequencies can be good. >> >> Jack K8ZOA >> >> >> Jim Brown wrote: >> >>> On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote: >>> >>> >>> >>>> Yes, I have several ferrite core 2.5 mH chokes here, including the >>>> Hammond one you mention. There's a significant difference in high >>>> frequency performance of the pi wound on ceramic form versus the smaller >>>> pi-wound over ferrite and that's one of the things I'm hoping to >>>> illustrate in the article. >>>> >>>> >>> The RFI and Ferrite tutorial on my website includes clear explanations of >>> the nature of ferrite materials from a circuit point of view. You may find >>> it helpful in explaining why your very correct in your analysis. You are >>> welcome to cite it as a reference. >>> >>> http://audiosystemsgroup.com/RFI-Ham.pdf >>> >>> However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 >>> MHz. >>> >>> 73, >>> >>> Jim Brown K9YC >>> >>> >>> >>> _______________________________________________ >>> 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 >> > > > 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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Good point. That's why ferrite beads make good parasitic suppressors -
at VHF frequencies they act more like resistors than inductors. Where I ran into this problem was trying to come up with a plate choke for a kilowatt amplifier that would work from 1.8 to 19.7 MHz. The high inductance needed for the 160 meter band pretty much guaranteed poor performance at 10 meters. I couldn't make the choke lossy because it would burn up at those power levels. The solution was to use two chokes in series and select values that resulted in a series resonance that fell safely in between amateur bands. Al N1AL On Thu, 2008-07-31 at 10:34, Jack Smith wrote: > Indeed such is the case, and it is quite pronounced with high Q inductors. > > You may wish, however, to model and/or measure two series chokes when > both are wound on lossy ferrite material. The response looks quite > different. The resistance in parallel with the inductors radically > modifies the response when the material causes the inductor Q to be < 1. > > I'll E-mail you some early measurements and a quick simulation plots. > > Jack K8ZOA > > Alan Bloom wrote: > > When you wire two chokes of different value in series, you almost always > > get a series-resonant "hole" in the attenuation somewhere between the > > parallel-resonant frequencies of the two chokes. It's not hard to see > > why that's true if you model each choke as an ideal inductor in parallel > > with a capacitor. So you need to design the combination so that the > > series-resonant frequency falls somewhere unimportant. > > > > Al N1AL > > > > > > On Thu, 2008-07-31 at 09:14, Jack Smith wrote: > > > >> Jim: > >> > >> Thank you for the reference. > >> > >> Indeed, the self-resonant frequency of the typical small (FT50 size) > >> chokes I've wound are in the 5-10 MHz range, but at 100 MHz some > >> (depending upon the core material) still show enough Z to be useful. > >> For truly wideband 10 KHz - 100 MHz choke action, it's necessary to > >> series two wound with different core material and turns, e.g., 35 turns > >> on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on > >> FairRite 43 material for > 50 MHz. > >> > >> You have to pay particular attention to the u' and u'' values of the > >> ferrite material and how they change with frequency as this is a case > >> where core loss at high frequencies can be good. > >> > >> Jack K8ZOA > >> > >> > >> Jim Brown wrote: > >> > >>> On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote: > >>> > >>> > >>> > >>>> Yes, I have several ferrite core 2.5 mH chokes here, including the > >>>> Hammond one you mention. There's a significant difference in high > >>>> frequency performance of the pi wound on ceramic form versus the smaller > >>>> pi-wound over ferrite and that's one of the things I'm hoping to > >>>> illustrate in the article. > >>>> > >>>> > >>> The RFI and Ferrite tutorial on my website includes clear explanations of > >>> the nature of ferrite materials from a circuit point of view. You may find > >>> it helpful in explaining why your very correct in your analysis. You are > >>> welcome to cite it as a reference. > >>> > >>> http://audiosystemsgroup.com/RFI-Ham.pdf > >>> > >>> However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 > >>> MHz. > >>> > >>> 73, > >>> > >>> Jim Brown K9YC > >>> > >>> > >>> > >>> _______________________________________________ > >>> 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 > >> > > > > > > _______________________________________________ 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 Jack Smith-6
I've been looking for a pair of RFC's to bleed the static off of my parallel
feedline to ground. Have a couple of resistors, but would prefer a lower resistance DC path to ground. The antenna is used for the 160 through 6 meter ham bands and general coverage receiving so having something that would have a high impedance from 10 kHz to 100 MHz would be great. Would this type of choke be suitable? Darrell VA7TO K2 #5093 On Thursday 31 July 2008 09:14, Jack Smith wrote: > Jim: > > Thank you for the reference. > > Indeed, the self-resonant frequency of the typical small (FT50 size) > chokes I've wound are in the 5-10 MHz range, but at 100 MHz some > (depending upon the core material) still show enough Z to be useful. > For truly wideband 10 KHz - 100 MHz choke action, it's necessary to > series two wound with different core material and turns, e.g., 35 turns > on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on > FairRite 43 material for > 50 MHz. > > You have to pay particular attention to the u' and u'' values of the > ferrite material and how they change with frequency as this is a case > where core loss at high frequencies can be good. > > Jack K8ZOA > > Jim Brown wrote: > > On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote: > >> Yes, I have several ferrite core 2.5 mH chokes here, including the > >> Hammond one you mention. There's a significant difference in high > >> frequency performance of the pi wound on ceramic form versus the smaller > >> pi-wound over ferrite and that's one of the things I'm hoping to > >> illustrate in the article. > > > > The RFI and Ferrite tutorial on my website includes clear explanations of > > the nature of ferrite materials from a circuit point of view. You may > > find it helpful in explaining why your very correct in your analysis. You > > are welcome to cite it as a reference. > > > > http://audiosystemsgroup.com/RFI-Ham.pdf > > > > However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50 > > MHz. > > > > 73, > > > > Jim Brown K9YC > > > > > > > > _______________________________________________ > > 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 -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ 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 is probably drifting away from Elecraft specific topics, but a
quick answer to your question is "maybe yes or maybe no." The issue is what happens when one puts large RF voltages across these lossy ferrite-based chokes. In my application, it isn't an issue but it certainly can be as was mentioned earlier in, e.g., a plate choke environment or in your case where high voltage across parallel feed lines is possible. I would be hesitant to use this design across a parallel transmission line without first measuring the impedance of the chokes over the transmitting frequency range and evaluating the expected voltage across the chokes and the consequent power dissipation in the cores. There's also a possible concern with the chokes generating harmonics if driven into or close to magnetic saturation. Sorry to not be able to give a direct answer but it's not a questions permitting a yes or no response. Jack K8ZOA Darrell Bellerive wrote: > I've been looking for a pair of RFC's to bleed the static off of my parallel > feedline to ground. Have a couple of resistors, but would prefer a lower > resistance DC path to ground. The antenna is used for the 160 through 6 meter > ham bands and general coverage receiving so having something that would have > a high impedance from 10 kHz to 100 MHz would be great. > > Would this type of choke be suitable? > > Darrell VA7TO K2 #5093 > > On Thursday 31 July 2008 09:14, Jack Smith wrote: > > 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 Alan Bloom
On Thu, 31 Jul 2008 09:42:16 -0700, Alan Bloom wrote:
>That's why ferrite beads make good parasitic suppressors - >at VHF frequencies they act more like resistors than inductors. EXACTLY! The equivalent circuit of a wire going through a ferrite bead is a low Q parallel resonant circuit. (For some ferrite materials, its two parallel resonant circuits in series.) When we wind multiple turns through or around a core, we increase the capacitance between turns and multiply the inductance and loss by N squared, both of which serve to move the resonance down in frequency and increase the R at resonance. For all practical purposes, Q changes only to the extent that u' and u'' are changing with frequency. Thus, a material like Fair-Rite #43 which for most form factors has a resonance around 200 MHz can provide effective suppression at HF by winding multiple turns through it. The tutorial includes a development of the equivalent circuit (this work is original with me, and was first published in an AES Paper, also on my website). 73, Jim Brown K9YC _______________________________________________ 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 |
Re: RF Chokes (renamed)
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In reply to this post by Jack Smith-6
Jack Smith wrote on Thursday, July 31, 2008 at 7:08 PM:
> There's also a possible concern with the chokes generating harmonics if > driven into or close to magnetic saturation. Jack's warning is one good reason why chokes wound on ferrite cores, or powdered iron cores, for use as 'static bleeders' have to be designed very carefully if IMD generated by the chokes themselves is not to become a problem when they are subjected to strong signals e.g. AM broadcast as one example. At low values of magnetic flux within the core the level of IMD products might be acceptable, but not so at high values of flux. Without going into detail two good guidelines are to use as many turns as possible for the required inductance which requires lower values of core mu, and use a large diameter core not simply stack small cores. A similar situation exists in a particular receiver's front end L-C filters where T94-10 cores are used to maintain an IMDDR3 of 120db at 7 MHz. IMHO non inductive resistors are still the best bet for draining static. My apology if this has been said already, I have been away. 73, Geoff GM4ESD _______________________________________________ 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 Alan Bloom
On Thu, 31 Jul 2008 09:10:54 -0700, Alan Bloom wrote:
>When you wire two chokes of different value in series, you almost always >get a series-resonant "hole" in the attenuation somewhere between the >parallel-resonant frequencies of the two chokes. It's not hard to see >why that's true if you model each choke as an ideal inductor in parallel >with a capacitor. But that's not an accurate model! If ferrite chokes are wound on the "right" ferrite material (the mix), they have a dominant RESISTIVE component in the frequency range of interest. While it IS important to consider the series L-C possibility, in REAL chokes, the resistive component can prevent this from being a problem. Indeed, this goes back to the original comment that the important property of a ferrite choke is RESISTANCE, NOT inductance! A properly designed choke (that is, right number of turns, winding style, and using the "right" material) can be made to have a high resistive impedance over at least an octave, and Fair-Rite's #31 is good for at least two octaves. Again, see my tutorial, which also shows how simple curve fitting in a spreadsheet can be used to come up with actual R, L, and C values from magnitude-only impedance data. It also shows a method of measurement that is much better than commonly accepted "standards," like the HP Z meters and network analyzers when the unknown Z is high. 73, Jim Brown K9YC _______________________________________________ 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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