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.n
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
Number of windings: 37
Coil diameter: 10.6 cm between the center 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 wirelength: 17.5 meter.
Number of windings: 38
Coil diameter: 10.6 cm between center windings
Wire: litz 660x0.04mm
Induction: 244 uH

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 
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) = 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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