More test about Slug Tuned Inductor
This page investigates some inductor I have got. As always one can never find andy info about the coils and there is no manufacture label either so I have to investigate more.

I have made 4 coils with different number of turns. I made 6, 8, 12, ans 28 turns.
There is a formula for coils I will use and I have the been using a LCR meter to measure the inductance of the 4 coils. The values are plotted in excel to form a curve and from the curve I can calculate the AL value.
Formula : L (nH) = AL*n2

Where:
L = inductance in nanohenrys
AL = inductance factor
n = number of turns

This first diagram show the inductance with the screw-slug removed.

The red curve is made by excel and is a trendline. The inductance vary from 150nH to 3263nH.
The formula of the trendline is 3.2833 x 2.0681
If you compare this formula to he first one you can see the similarity.
The exponent is very close to 2 and the AL value will therefore be 3.28

The next diagram show the inductance with the screw-slug screwed to the bottom position.

The red curve is made by excel and is a trendline.
The inductance vary from 457nH to 9113nH.
The formula of the trendline is 12.514 x 1.9734
The exponent is still very close to 2 and the AL value will therefore be 12.51

Conclusion: The ferrite slug core raise the AL from 3.3 to 12.5, depending on how deep it is screwed into the coil.
The tables below show the complete data. The position of the slug-core is in percent of the total lengt of the core. If there is no core the value is 0% and if the complete core is screwed into the coil the value is 100%

 n = 6 Core position (%) Inductance (nH) 0% (no core) 150 16% 170 33% 209 50% 285 67% 372 83% 440 100% (max core) 457

 n = 8 Core position (%) Inductance (nH) 0% (no core) 198 16% 217 33% 265 50% 341 67% 464 83% 657 100% (max core) 700

 n = 12 Core position (%) Inductance (nH) 0% (no core) 624 16% 640 33% 690 50% 837 67% 1091 83% 1425 100% (max core) 1701

 n = 16 Core position (%) Inductance (nH) 0% (no core) 982 16% 1056 33% 1265 50% 1650 67% 2154 83% 2659 100% (max core) 2957

 n = 28 Core position (%) Inductance (nH) 0% (no core) 3263 16% 3546 33% 4110 50% 5199 67% 6728 83% 8240 100% (max core) 9113

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