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List:       elecraft
Subject:    Re: [Elecraft] K3 6m pre-amp
From:       Darrell Bellerive <va7to () yahoo ! ca>
Date:       2008-07-31 17:43:11
Message-ID: 200807311043.11407.va7to () yahoo ! ca
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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
> >
> >
> >
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-- 
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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