Experiments with LC circuits  part 4

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From tuning capacitor C1b I now removed the insulation rings which keeps the stator on it's place.
I found that the used nylon screws gave some dielectric losses which reduces circuit Q.
Now I use instead a polyethene block which supports the stator from the underside.
In the following drawings this is shown., this version of tuning capacitor I call: C1c.

Tuning capacitor C1b  1= frame of tuning capacitor 2= plastic insulation ring 3= nylon screw 4= polyethene insulation block 5= copper connection bar for stator plates 6= stator plates

Tuning capacitor C1c 1= frame of tuning capacitor  2= copper connection bar for stator plates 3= metal screw 4= polyethene block 5= polyethene bottom plate 6= nylon screw 7= stator plates

The plastic insulation blocks of tuning capacitor C2 are replaced by polyethene blocks (which are the green blocks on the next picture).

Left: C1c  (495 pF). Right: C2a (390 pF).

After these changes, I measured the Q's again, they were increased.
The percentages of increase are also mentioned, compared to measurement 21 and 22.

Now I have drilled a lot of 2 mm holes in the polyethene insulation blocks of tuning capacitor C2a.
Hoping that removing insulation material will reduce dielectric losses even more.
This version of tuning capacitor is called: C2b.

The percentages mentioned are compared to measurement 24.
At 600 kHz there is a decrease in Q, how that comes, I don't know.
Maybe there was a measuring error in measurement 24, normally the accuracy of the measured values are I think between +5% and -5%, but maybe this time the error is higher.

Or maybe the Q is really reduced at 600 kHz, this is no problem, at low frequencies a Q above 1000 is more than enough.

"Tot lering en vermaak"  That's an old Dutch expression which means "for learning and fun".
And that's why I made the following two measurements with lower Q coils, often used in crystal receivers.

Coil L10 13 meters litzwire 40x0.07mm on a former made of a CD. The shiny aluminium layer is fully removed from the CD. Coil L11 70 turns on a toilet paper roll. Wire: massive 0.8mm enamelled copper wire. Wire length: about 10.5 meters. The windings are not laying nice side by side, because it was used (old) wire with lots of bendings.

The used tuning capacitor is C2b.

* = not measured.
The measured values are not bad at all, but keep in mind that a very good tuning capacitor is used.
So, a good comparison with measurement 1 to 16 is not possible, also because the test method used now is much better.

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