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)
where
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)
where
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?
Regards,
Peter, G3LDO
e-mail <[email protected]>
Web <http://web.ukonline.co.uk/g3ldo>
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