Experiments with LC circuits part 8
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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
wirelength 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 sideplates, and 48 strips where the wires
are running over. The material of the coilformer is polypropylene 
Coil L19 Total wirelength: 17 meters

Measurement 
LC combination 
F min 
F max 
Q 
Q 
Q 
Q 
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 wirelength: 17.5 meter. For 37 windings a wirelength of 17 meters is enough, the last 0.5 meter is wound as a 38th winding over the strips. 
Measurement 
LC combination 
F min 
F max 
Q 
Q 
Q 
Q 
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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