Toroid Cores

Powdered-Iron Toroidal-Cores

Magnetic properties

Inductance and Turns formula
The turns required for a given inductance or a inductance for a given number of turns can be calculated from:
N=100 √ L/AL  or   L=AL{N2/10.000}
Were N = number of turns;
L = desired inductance (μH)
AL = inductance index (μH per 100 turns)
AL Values (μH per 100 turns)
MIX
  Size 
26
   3    
   15  
    1  
   2   
   7  
   6   
   10  
   12  
   17  
   0  
T-12

    na

  60

  50

  48

  20

  18

 17

 12

7.5

7.5

3.0

T-16

 145

  61

  55

  44

  22

  na

 19

 13

8.0

8.0

3.0

T-20

 180

 76

  65

  52

  27

  24

 22

 16

10.0

10.0

3.5

T-25

 235

 100

  85

  70

  34

  29

 27

 19

12.0

12.0

4.5

T-30

 325

 140

  93

  85

  43

  37

 36

 25

16.0

16.0

6.0

T-37

 275

 120

  90

  80

  40

  32

 30

 25

15.0

15.0

4.9

T-44

 360

 180

 160

 105

  52

 46

  42

 33

 18.5

 18.5

 6.5

T-50

 320

 175

 135

 100

  49

  43

  40

  31

 18.0

 18.0

 6.4

T-68

 420

 195

 180

 115

 57

  52

  47

  32

 21.0

 21.0

 7.5

T-80

 450

 180

 170

 115

 55

  50

  45

  32

 22.0

 22.0

 8.5

T-94
 590
 248
 200
 160
 84
  na
  70
  58
 32.0
 na
 10,6

 Magnetic Properties Iron Powder Cores
Most powdered-iron toroid-cores that radio amateurs use are manufactured by Micrometals, who uses paint to identity the material used in the core. The Micrometal color code can find in the table below.
Mix
Color
Material
 μ
Temp stability
(ppm/0C)
 f (MHz)
Notes
 26
 yellow/white
 hydrogen reduced
75
 825
 dc – 1
 Used for EMI filters and dc chokes
 3
 gray
 carbonyl hp
 35
 370
0,05 – 0,50
 Excellent stability, good Q for lowe frequencies
 15
 red/white
 carbonyl gs6
 25
 190
 0,1 – 2
 Excellent stability, good Q
 1
 bleu
 carbonyl c
 20
 280
 0,5 – 5
 Similar to mix 3, but better stabillity
 2
 red
 carbonyl e
 10
 95
 2 – 30
 High Q material
 7
 white
 carbonyl th
 9
 30
 3 – 35
 Similar to MIX-2 and Mix-6, but better temp stabillity
 6
 yellow
 carbonyl sf
 8
 35
 10 – 50
 Very good Q and temp. stability for 20 – 50 Mhz
 10
 black
 Powdered-iron W
 6
 150
 30 – 100
 Good Q and stability for 40 – 100 MHz
 12
 green/white
 Synthetic oxide
 4
 170
 50 – 200
 Good Q, moderate temp stability
 17
 bleu/yellow
 carbonyl
 4
 50
 40 – 180
 Similar to Mix-12, better temp. stability, Q drops about 10% above 50 MHz, 20% above 100MHz
0
tan
phenolic
1
0
100 – 300
 Inductance may vary greatly with winding technique