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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Wed, 21 Mar 2018 09:33:23 +0000
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To: LineOne <rsgb_lf_group@blacksheep.org>
Cc: rsgb_lf_group <rsgb_lf_group@yahoogroups.co.uk>
Subject: Re: LF: Idea for tuned inductor
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That should read:

Inductance = uo * A / g * N^2
where uo is mag permeability of free space, 4E-7 * pi,    A is the core
area and g the adjustable gap  (SI units) and N the number of turns

'jnt


On 21 March 2018 at 09:22, Andy Talbot <andy.g4jnt@gmail.com> wrote:

> Looking at some large pot cores , I was struck by this novel idea.
>
> Back in the very early days of 10GHz with wideband equipment, we tuned
> Gunn oscillator using a dielectric probe on a micrometer head - that
> allowed precise adjustment with a repeatable reading.    Looking at my
> gapped pot cores, it occurred to me something similar could be done with
> them.
>
> Fix, somehow, one half core to the micrometer so it can me pulled away
> from the other allowing a precise air gap.  Of course, doing it this way
> means you have a gap in outer and inner pieces, so the effective gap is
> double the measured value
>
> Inductance is then uo * A / g    where uo is mag permaeability of free
> space, 4E-7 * pi   A is the core area and g the adjustable gap  (SI units)
>
> You'd have to watch out for saturation (V= 4.44 . N.A.B) but as a small
> adjuster to a larger fixed loading coil at low frequencies,  may have some
> merit for fine repeatable setting
>
> Just a thought
>
> Andy  G4JNT
>

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<div dir=3D"ltr">That should read:<div><br></div><div><span style=3D"color:=
rgb(34,34,34);font-family:arial,sans-serif;font-size:small;font-style:norma=
l;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;le=
tter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;wh=
ite-space:normal;word-spacing:0px;background-color:rgb(255,255,255);text-de=
coration-style:initial;text-decoration-color:initial;float:none;display:inl=
ine">Inductance =3D uo * A / g * N^2=C2=A0 =C2=A0=C2=A0</span></div><div><s=
pan style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:sma=
ll;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal=
;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;tex=
t-transform:none;white-space:normal;word-spacing:0px;background-color:rgb(2=
55,255,255);text-decoration-style:initial;text-decoration-color:initial;flo=
at:none;display:inline">where uo is mag permeability of free space, 4E-7 * =
pi,=C2=A0 =C2=A0 A is the core area and g the adjustable gap=C2=A0 (SI unit=
s) and N the number of turns</span></div><div><br></div><div>&#39;jnt<br><d=
iv><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On 21 Marc=
h 2018 at 09:22, Andy Talbot <span dir=3D"ltr">&lt;<a href=3D"mailto:andy.g=
4jnt@gmail.com" target=3D"_blank">andy.g4jnt@gmail.com</a>&gt;</span> wrote=
:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-le=
ft:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">Looking at some large =
pot cores , I was struck by this novel idea.<div><br><div>Back in the very =
early days of 10GHz with wideband equipment, we tuned Gunn oscillator using=
 a dielectric probe on a micrometer head - that allowed precise adjustment =
with a repeatable reading.=C2=A0 =C2=A0 Looking at my gapped pot cores, it =
occurred to me something similar could be done with them.</div></div><div><=
br></div><div>Fix, somehow, one half core to the micrometer so it can me pu=
lled away from the other allowing a precise air gap.=C2=A0 Of course, doing=
 it this way means you have a gap in outer and inner pieces, so the effecti=
ve gap is double the measured value</div><div><br></div><div>Inductance is =
then uo * A / g=C2=A0 =C2=A0 where uo is mag permaeability of free space, 4=
E-7 * pi=C2=A0 =C2=A0A is the core area and g the adjustable gap=C2=A0 (SI =
units)=C2=A0</div><div><br></div><div>You&#39;d have to watch out for satur=
ation (V=3D 4.44 . N.A.B) but as a small adjuster to a larger fixed loading=
 coil at low frequencies,=C2=A0 may have some merit for fine repeatable set=
ting</div><div><br></div><div>Just a thought</div><div><br></div><div>Andy=
=C2=A0 G4JNT</div></div>
</blockquote></div><br></div></div></div></div>

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