Java Projects

Air Core Coil Design

Revised 7/21/97

Preface

This calculator helps you to design a single-layer air core coil of a given inductance. The formulae come from the ARRL Handbook for Radio Amateurs. These formulae provide close approximations of values for frequencies in the 1-30MHz range which are sufficiently accurate for most amateur radio purposes. The calculations are useful in the VHF and UHF range by only as a basis for further calculation and experimentation.

Turns per Inch

This program designs close-wound coils. For turn spacing (Turns per Inch) choose one of the following:

• Bare Wire - Enter the guage, then double the diameter. During assembly, use a length of the same size wire as a spacer between turns.
• Enamelled Wire - Manually add 0.005" to the diameter.
• Insulated Wire - Either measure the OD including insulation and enter this directly, or wrap several turns around a ruler and enter the turns per inch.

In all cases, spread the winding evenly over the calculated winding length before securing in place.

Standard Forms

Standard plastic water and drain pipe is available in the following outside diameters:

0.66", 0.88", 1.66", 1.90", 2.38", 2.88", 3.50", 4.50"

Coil Design

To calculate diameter and number of turns:

1. Determine turns per inch.
• Enter AWG # for bare or enamelled wire. Note the resistance in Ohms per inch for the wire chosen.
• Adjust diameter: add 0.005 for enamelled, double for bare wire.
• For insulated wire, wrap a form and count the turns per inch. Enter turns per inch directly for insulated wire.
2. Enter the desired micro-Henries of inductance.

To calculate actual inductance for a standard sized wire form and whole number of turns:

1. Adjust coil diameter to a standard form. If you will make a form, you must still enter a number for diameter (possibly the number given as output).
2. Adjust the number of turns to the nearest integer
3. Note the total length of wire. Compute total length * ohms per inch to get the overall resistance of the coil.