Air Coil Calculation
This side will explain how to calculate coils and will explain how you can make your own coils.
I have made coils with different number of turns and measured the inductance.
All contribution to this page are most welcome!


Formula :










Where:
L = inductance in microhenrys
d = coil diameter in inches(from wire center to wire center)
l = coil length in inches ( 1 inches = 25.4 mm)
n = number of turns
There are lots of Internet-pages explaining how to make coils, but there are few that will give you exact values. I have been experimenting with different diameters, length and wire-diameter and found one good combination. I have been using Hewlett Packard 4192A LF Impedance Analyzer to measure the coils. To make the coils, I have used a two drills with a diameter of 7.2mm and 5.8mm. The diameter is chosen to give wide range of inductance and the coils will get good Q-values. The wire for the coils has a diameter of 0.6mm. The diameter of the wire is not so critical. The tables below shows the results.

INDUCTANCE TABLE (diameter 7.2 mm, 0.6mm wire)
Number of turns Inductance (nH)
(Compact coil)		 Q-value 13-MHz
(Compact coil)		 Inductance (nH)
(Air-space coil)		 Q-value 13-MHz
(Air-space coil)
37740766440
4122325102560
5177340--
6240440206550
7306509290690
83796073191300
94701500422>1500
10582>1000515>1000
11644>1000->1000
12656>1000545>1000
13745>1000612>1000
14789>1000658>1000




INDUCTANCE TABLE (diameter 5.8 mm, 0.6mm wire)
Number of turns Inductance (nH)
(Compact coil)		 Q-value 13-MHz
(Compact coil)		 Inductance (nH)
(Air-space coil)		 Q-value 13-MHz
(Air-space coil)
49254079-
5131370120530
6175340155500
7220300184640
8272370234560
9315470267770
103636503131270
The coil can be compact with no space between the winding or you can pull it out, to make some space between the windings. My measurements shows that you will get the best Q-value if you pull out the winding so the air-space is 0.6mm between the turns in the winding. The inductance will drop a little, se the table above.

* Compact = There is no space between the windings in the coil!
* Air space= There is an air-space between the winding with the same length as the diameter of the wire you are using (0.6mm in this case).

Improved LC-meter KIT
Front side
Here you have it. Few parts and perfect function.
Link visit my LC meter project.
Back side
Here you have it. Few parts and perfect function.
Link visit my LC meter project.



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