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A radio frequency (RF) choke, also known as an inductor, blocks signals of a certain frequency. If you're building or repairing radio equipment, you can make your own chokes. You'll need a form on which to wind the inductor, wire and a calculator.

## Form

Wind the choke on a cylindrical form made of an insulator such as plastic or ceramic. You can use forms bought off-the-shelf or made from household odds and ends. The form's diameter helps determine the choke's inductance value. A hollow-centred form can accept an iron core, which increases the choke's inductance.

• Wind the choke on a cylindrical form made of an insulator such as plastic or ceramic.
• A hollow-centred form can accept an iron core, which increases the choke's inductance.

## Wire

Magnet wire--copper wire with a thin insulating varnish coating--makes good material for making chokes. The thin insulation wastes little space when you need to make hundreds of wire turns on the form. Use a wire thin enough to save space but thick enough to carry sufficient current.

## Calculations

Before you wind a choke, you'll need to know its inductance value in microhenrys. Use the formula (D^2 x N^2) / [(18 x D) + (40 x Z)], where D and Z are diameter and length in inches, respectively, and N is the number of turns.