Experiments with LC circuits  part 8

A piece of theory:

One wire winding has a certain induction "L".
If we give the coil more windings (number of windings= n, so the total wire length is n times as long), and the magnetic coupling between the windings is very good, then the total induction will be: L.n²
If there is no magnetic coupling between the windings at all, then the total induction will be:  L.n
With some magnetic coupling the induction will be somewhere between these values.

For getting much induction, we must have much magnetic coupling between the windings by placing them close on each other, like in coil  L16.

But with the windings close on each other, the capacity between the winding also increases, so we can't reach a high tuning frequency.
Also dielectric losses increases, caused by the insulation of the wires, which reduces circuit Q.

A  3 dimensional coil

Now I constructed a coil where the windings are both placed besides and above each other, in a kind of 3 dimensional structure.
This reduces the distance between the first and the last windings, (compared with a spiderwebcoil with thick wire) this should increase the induction.
Between the windings there is a air spacing, the windings are not touching each other at any point.

 The windings are placed both beside and above each other. The sequence of the windings is indicated by the small dashes. This coil has 37 windings.

De windings have a fixed position, independent of the wire diameter.

 The coilformer is made of two side plates, and 48 strips where the wires are running over. The material of the coilformer is polypropylene

 Coil L19  Total wire length: 17 meters Number of windings: 37 Coil diameter: 10.6 cm between the centre windings Wire: litz 40x0.07 Induction: 229 uH
 Measurement  number LC combination F min  kHz F max  kHz Q 600 kHz Q 900 kHz Q 1200 kHz Q 1500 kHz 81 L19 C2b 532 1976 342 349 433 455

Compared to spiderwebcoil L10 coil L19 has less induction, but higher Q at higher frequencies.

 Coil L20 Total wire length: 17.5 meter. Number of windings: 38 Coil diameter: 10.6 cm between centre windings Wire: litz 660x0.04mm Induction: 244 uH For 37 windings a wire length of 17 meters is enough, the last 0.5 meter is wound as a 38th winding over the strips.
 Measurement  number LC combination F min  kHz F max  kHz Q 600 kHz Q 900 kHz Q 1200 kHz Q 1500 kHz 82 L20 C2b 515.7 1872 1304 1304 1142 914

Coil L20 has a little bit more induction than spiderwebcoil L13 which has also 17.5 meters wire.
The Q of L20 is comparable with spiderwebcoil L13.

L20 has 17.5/17.0= 1.029 times more wire then L19.
The induction of L20 should then be  (1.029)² = 1.059 times higher than the induction of L19, so 1.059 x 229uH =242.7 uH.
This comes close to the value of L20, from this I conclude that the kind of wire has not much influence on induction.

After measurement 18  my conclusion was that wire diameter did have much influence on induction.
But this has probably more to do with the fact that with thick wire, the coil gets a larger outside diameter.
This reduces the coupling between the inside and the outside windings, and so decreases induction.

But when the wires has a fixed position, the wire thickness has little influence on induction.

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