Winding an air-core coil
How many turns on which former: inductance from diameter, length and number of turns, plus wire length and turn spacing.
Winding an air-core coil
Single-layer solenoid after Wheeler. Accurate enough for matching networks and common-mode chokes, as long as the coil is longer than half its diameter.
How the page calculates
- L = 0.3937 ยท rยฒ ยท nยฒ / (9r + 10l) (L in ยตH, r and l in cm)
- Wire length = n ยท ฯ ยท d
The formula is Wheeler's (1928) and applies to single-layer solenoids that aren't too short. Below about l = r the value comes out clearly too high; the calculator then warns you. Instead of the turns you can also enter the inductance you want, and it works out the turns needed.
Related terms
- Common-mode choke
- stops current on the outside of the coax shield and with it RF in the house
- Balun
- transition between a balanced antenna and an unbalanced cable
- Unun
- transformer between two unbalanced systems, often used with end-fed antennas