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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Wed, 21 Mar 2018 09:22:11 +0000
Message-ID: <CAA8k23T_tfBA+h+Qo2sO8=bYU-rk5pmiC=UGVmjmPxYV93ddxg@mail.gmail.com>
To: rsgb_lf_group <rsgb_lf_group@yahoogroups.co.uk>,
        LineOne <rsgb_lf_group@blacksheep.org>
Subject: LF: Idea for tuned inductor
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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">Looking at some large pot cores , I was struck by this nov=
el idea.<div><br><div>Back in the very early days of 10GHz with wideband eq=
uipment, 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 cou=
ld be done with them.</div></div><div><br></div><div>Fix, somehow, one half=
 core to the micrometer so it can me pulled 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 effective gap is double the measured value<=
/div><div><br></div><div>Inductance is then uo * A / g=C2=A0 =C2=A0 where u=
o is mag permaeability of free space, 4E-7 * pi=C2=A0 =C2=A0A is the core a=
rea and g the adjustable gap=C2=A0 (SI units)=C2=A0</div><div><br></div><di=
v>You&#39;d have to watch out for saturation (V=3D 4.44 . N.A.B) but as a s=
mall adjuster to a larger fixed loading coil at low frequencies,=C2=A0 may =
have some merit for fine repeatable setting</div><div><br></div><div>Just a=
 thought</div><div><br></div><div>Andy=C2=A0 G4JNT</div></div>

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