KFF Homebrew Tips


Subject: Make Your Own Loading Coils DE KFF


OR: "If they look like DUX and walk like DUX and quack like DUX, maybe they


(then again maybe not)


"Air Dux" inductors were once plentiful and inexpensive. Not so today. Even if they were, HAMs

like to make their own apparatus when possible. Here is one method that I have long used to

make evenly spaced, nice looking coils of all sizes.



Make your own loading coils for antenna projects using Caterpillar Grommet

strips. Also called flexible grommets, flexible bushings etc.

These are used by installers to form protective bushings around the edges of holes cut into sheet metal,

and come in strips that are cut to desired length then snapped into the hole to cover the raw edge.

We used to use them when installing 2-way radios to line the holes we made in the firewall to pass the heavy 12V wires.

The evenly spaced notches make an ideal form and support for AIR DUX knockoffs. Use Duco or Testors model

cement to secure the wires in the strips before removing from the temporary

forms. Nylon Grommet strips can be purchased at McMasters, as well as many other supply houses.



Fig 1 is the caterpillar grommet material as purchased from the supplier:



Fig 2 - Next Wrap the form (whatever size you need) in wax paper and temporarily

tape the plastic strips on there:




Fig 3 -Wind the coil using the notches as a guide. Seat the wire all the way down

into the notch and wrap the coil tightly. Spread plastic cement down the

strips when the coil is wound: 

Fig. 4 - When the glue is dry, slip the assembly off the form and trim the strips to

correct length:



Fig 5 - Any size diameter or length can be wound, just use bigger forms and more



Happy Building, Geo>KFF