Slug Tuned Inductor

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.
All contribution to this page are most welcome

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 A_L value.
Formula : L (nH) = A_L*n²

Where:
L = inductance in nanohenrys
A_L = 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 A_L 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 A_L value will therefore be 12.51

Conclusion: The ferrite slug core raise the A_L 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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