Message-ID: <200901311642330609.13E0A7CD@smtp.wanadoo.fr>
In-Reply-To: <172D99CA495841DC87784DBC9160975A@JimPC>
References: <200901291143090013.08822D48@smtp.wanadoo.fr>
 <172D99CA495841DC87784DBC9160975A@JimPC>
Date: Sat, 31 Jan 2009 16:42:33 +0100
From: "John RABSON" <john.rabson@wanadoo.fr>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: Ferrite toroid cores using HEM series materials
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Paul, David, Alan, Jim, LF, (and anyone I may have left out)

Many thanks everyone for your replies and very useful information.  What kic=
ked my request off was the need to make an input transformer for the Softroc=
k for 136.

I have a few of these cores (and also assorted cores inherited from one of o=
ur club members in Suffolk) and will do some measurements. =20

73
John F5VLF

*********** REPLY SEPARATOR  ***********

On 29/01/2009 at 22:03 James Moritz wrote:

>Dear John, LF Group,
>
>Most of these "EMC" cores are made of something similar to Fair-Rite #43=20
>material, with mu of around 850. They will work quite well at LF and MF,=20
>although a given size of core will require about 1.5 times as many turns
>as=20
>the "traditional" 3C85/90/95 etc materials to get the same inductance.=20
>Unfortunately, the distributors have only heard of ferrite cores being
>used=20
>to put on cables to supress noise, so they don't know much about
>materials,=20
>and usually classify according to size, and, if you are lucky, impedance
>in=20
>the HF/VHF range, which is not very relevant to LF.
>
>You can make a reasonably accurate determination of the permeability by=20
>measuring the inductance of a core wound with several turns to get AL =3D L
>/=20
>n^2, The formula relating AL, mu, cross-sectional area, and magnetic path=20
>length is
>
>AL =3D 4pi * 100 * mu *A/l
>
>with cross sectional area of the magnetic path A in square metres, and=20
>magnetic path length l in metres  (in the case of toroidal shapes, this is=20
>roughly the average of the inner and outer circumferences of the core),
>and=20
>mu is the relative permeability.
>
>Once you know what permeability you have, you can be fairly sure behaviour=20
>will be near to that of a material with similar mu in one of the=20
>manufacturer's catalogues, e.g. Ferroxcube or Fair-Rite
>
>Cheers, Jim Moritz
>73 de M0BMU