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Re: [TowerTalk] [RFI] HIGH POWER and RFI...

To: "Jim Brown" <>,
Subject: Re: [TowerTalk] [RFI] HIGH POWER and RFI...
From: "Dan Zimmerman N3OX" <>
Date: Tue, 6 Mar 2007 10:55:27 -0500
List-post: <>
On 3/6/07, Jim Brown <> wrote:
> On Tue, 6 Mar 2007 09:06:45 -0500, Dan Zimmerman N3OX wrote:
> >measures, inaccurately, on my MFJ-259
> Ferrite chokes are essentially very low Q parallel resonant
> circuits. Antenna analyzers are not very useful for measuring
> ferrite chokes,


I didn't mean to detract from the suggestion to look at your very good
tutorial...  that's excellent work and very useful.

I just had measured the Radio Shack cores particularly (and they don't say
on the package what material they are) so I figured it might be useful to
compare with manufacturer data on other cores.

>Second, antenna analyzers are essentially SWR analysers, and have
>their greatest accuracy when the unknown Z is close to their
>design impedance

When I'm trying to make a choke at home on a random core, I put a number of
turns on the core that comes as close as possible to mid-range impedance and
then I calculate from there if I'm shooting for a particular impedance.

For example, I might be reasonably confident that my SWR analyzer can
measure 36+j60 with sufficient accuracy.  I know the impedance of three
turns and can scale up within reason.  It's much better, for sure, to choose
proper cores and design from manufacturer data or the data in your tutorial,
but if you've got some nice big random cores at home and need to know what
they are, I think the SWR analyzer is not *entirely* useless, if you keep
the limitations you pointed out in mind.

Might give you the ability to identify your random core by looking at
manufacturer data.

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