Experiments with LC circuits part 3

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The next step in improvement of the LC circuit is the use of litzwire with very much strands.
The next coil is made with litz 660x0.04mm (also called 660/46,  660 is the number of strand, the wiresize is 46 AWG = 0.04 mm).

Coil  L9 Wirelenght on the coil: 14.5 meter and two leads of 0.25 m. Total wirelenght: 15 meter. Inside coildiameter: 6 cm. Outside coildiameter: 16 cm. (coilformer is 20 cm diameter). Number of windings: 41 Wire: litz 660x0.04mm Coilformer material: 3mm foam PVC Induction: about 175 uH.

One measurement is made with capacitor C1b, and one with C2.

Conclusion:

C1b gives a higher Q then  C2, this is strange, in  measurement 5 and 6 C2 gives the highest Q.
Coil L9 has a lower induction then e.g. coil L5 (F min is higher), though L9 has more wirelenght.
The 660x0.04 litz seems to give less induction then the 40x0.07 litz.
The Q of L9 is much higher then the coils made with 40x0.07 litz.

Until now the Q measurements were made with a 1:100 probe between LC circuit and oscilloscope.
The test setup is discribed here as test setup 2.
But I found that the testprobe has a negative effect on the Q.

In the next measurement I use a self-made FET amplifier between the LC circuit and the oscilloscope.
The test setup is described here as test setup 3

The same circuits are now measured again.

By using the FET amplifier, the Q increases, especially at high frequencies.

When measuring high Q circuits, the frequency of the signal generator must be adjusted very accurate.
With the sweep signal generator I used this was not easy, so the values of Q were not reliable.
Now I replaced the sweep generator by a DDS generator, at which the frequency can be very accurate set.
The test setup you will find here as test setup 4.
With the use of the DDS generator I measured the Q's again of the same circuits:

The Q's in measurement 21 and 22 are mostly lower than in measurement 19 and 20, this is caused by the inaccuracy of measurements until number 20.
The measurements 17-18 and 19-20 and 21-22 are all done withe the same LC circuits, only the used test equipment was different.

In my opinion measurement 21 and 22 give the most reliable Q values.
But the measurements before were also usefull because a increase or decrease of Q could be seen .

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