Variable Choke Coil

[Farlander]

Ok so I just had one of those stroke of epiphany moments where it hit me how to make a variable choke easily.

Wrap the bifilar wires around a core that has raised bridges in various locations.  This gets the wire up and away from the main coil.  Scrape some of the insulation back from the wire on top of the bridge, and tap into it.  Various taps should cause variable inductance, allowing you to play with the range of frequencies needed for resonant condition.  Push CTRL - to zoom out.  Good luck.

[HeairBear]

If you want one with a "wiper arm" you could use a variable transformer in a creative way. The windings are a 1:1 ratio, wound on the same core. and the wiper arm is already built in. Use the input side of the variable transformer for the positive side of the VIC and the output side to the negative side of the VIC.

[z.monkey]

Congratulations!

You just successfully re-invented the Variac...

http://www.variac.com/
http://en.wikipedia.org/wiki/Variac#Variable_autotransformers

[nievesoliveras]

Also there is the way of the radio antenna to make variable taps on the choke:

Jesus

[HeairBear]

WOW! You are one smart monkey! Here is a banana! (throws banana very far away)...