Electronics
Multi-layer air-coil design information

Air-Cored Multi-Layer Coils for Non-Critical Applications

Author: R.J.Edwards G4FGQ © 5th May 2002

A Multi-Layer Coil Design Program

Typical Coil Applications

  • Receiving antenna loading coils
  • Receiving antenna coupling transformers
  • Receiving preselectors
  • Circuit decoupling chokes
  • Interstage coupling transformers
  • Frequency response compensation
  • Frequency filters
  • Coaxial cable choke baluns
  • Very low power MF transmitters
  • Speaker crossover networks

Typical Winding Cross-Sections

  000
000 00000
000 00000
000 00000 00000
000 00000 00000 00000000
000 00000 00000 00000000
----- ------- ------- ----------
----- ------- ------- ----------
000 00000 00000 00000000
000 00000 00000 00000000
000 00000 00000
000 00000
000 00000
000

A coil is specified by inside diameter, outside diameter, axial length and number of turns. Turns disposition does not have a great effect on performance. Highest test frequency accepted is 3000 KHz.

For coil proportions similar to those on the previous screen, coil inductance is computed to within 5 or 10 percent. Accuracy is less for more extreme shapes such as basket-weave, pancake windings, or long single-layer solenoids but will be good enough for experimental purposes. If not, use programs such as solnoid3.

Solid copper wire is assumed, wire insulation increases overall diameter, turns can be wound simply layer on layer. Inductance will not be greatly affected by rough hand-winding though self-capacitance may increase above computed values.

Computed self-capacitance is a rough estimate. Different wire insulation thicknesses, scramble-winding and internal air-spaces are too uncertain to take into account accurately so some practical measurement experience has been included.

For a square winding cross-section set axial length to half the difference between inner and outer diameters. To approximate a circular bundle of conductors (a coax cable choke balun) set side of square to 90% of diameter of the bundle.

Q is fairly low due to skin and proximity effects. It may be improved somewhat by using Litz wire but for most purposes this will not be worth the trouble.

Note that the aspect-ratio of the winding cross section can be varied by using keys Z and X with a minimal effect on turns, wire gauge and inductance. This facility may assist organising the number of layers and turns per layer.

Run this Program from the Web or Download and Run it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link MultiLay then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.


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