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
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