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Re: LF: Decca Coils

To: [email protected]
Subject: Re: LF: Decca Coils
From: "Rik Strobbe" <[email protected]>
Date: Mon, 29 Oct 2001 16:13:14
In-reply-to: <[email protected]>
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Hello Peter,

I got 2 formulae from 'Grundlagen der Hochfrequenztechnik' :

1. For 'slim' coils (H>>D) : L = 2*Pi*N^2*D(3.47/(1+2.2*H/D)-K*C/H)


L = inductance (nH)
N = windings
D = average coil diameter (cm)
H = coil length (cm)
C = thickness of the wirelayers (all together, in cm)
K = correction factor depending on H/C ratio :
        L/C     K
        2       0.10
        3       0.15
        5       0.23
        10      0.27
        15      0.30
        20      0.31
        30      0.32

2. For 'fat' coils (H<=D) : L = 78*L^2*D/(3*D+9*H+10*C)

If the coil is not close wound then a correction factor dL has to be taken
into account : dL = 2*Pi*D*(ln(b/d)+0.155)
b = wire spacing (centre wire to centre wire)
d = wire diameter
ln = natural logaritm

dL has to be added to L (but since always b > d , dL will be negative).

I hope the above gives at least an idea where to start with,

73, Rik  ON7YD

I am dismantling a Decca loading coil with the objective of rebuilding it to
load my 16m high antenna. It will be converted so that it is a multi-layer
coil. Does anyone know of a formula for multilayer coils where the spacing
between the layers is several times the wire diameter?

Peter, G3LDO

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