[Lf] LF: Coil winding conundrum]

[Andre' Kesteloot]

"Soegiono, Gamal" wrote:

> Hello Andy G4JNT
>
> G4JNT> Both coils were the same diameter, same inductance, and roughly
> G4JNT> the same length in total.   So why was the one made of plain
> G4JNT> wire better ?   Self capacitance ?
>
> No. Unless the "capacity" exhibits significant dielectric losses,
> great self capacitance does not harm in lieu of Q.
>
> What you probably have missed is to keep distance between
> individual turns of the coil's winding. The effect of closely
> winded turns is named proximitty effect. Current in one turn
> tends to displace the current in the adjacent turn and vice versa.
>
> At "high" frequency AC we know the skin effect. That is, current
> flow concentates on the perifery (surface) of a relatively large wire
> diameter, rather than to evenly cover the total X-section
> of the wire as it does for DC.
>
> If more than one wires are arranged to lay one beside the other,
> the proximitty effect adds on in reducing the effecitve X-section
> by displacing current flow even more as the skin-effect alone already
> does.
>
> When constructing loop antenna windings, I try to keep a clearance
> of at least 2 times the wire diameter in between individual turns and
> always get optimum Q. For solenoid type of coils I recommend a minimum
> of 1 wire's diameter of clearance.
>
> As the self-made Litz wire has a greater outer diameter, it's
> relative close proximitty to the next turn reduces Q much more
> than in the case of the solid wire.
>
> I recommend you build a third coil similar to the first one, where
> you keep a clearance, equivalent of one/two wire diameters.
> Try to keep the same aspect (coil former diameter to winding length)
> as in coil 1. Would be interesting to know the actual difference in Q then.
>
> best 73 de Gamal
>