For over a century now, radio amateurs have made tuned circuits using a coil of wire and a variable capacitor. In recent decades the supply of variable capacitors has dwindled, as SDR technology has supplanted the traditional tuning capacitor. No more tuned circuits for the radio amateurs? Not quite, as [Bill Meara N2CQR] shows us in the video below the break by making variable inductors using permeability tuning. This is hardly high-tech, the major component is as simple as a glue stick.
A permeability tuned inductor has a core that is moved in and out of its center by means of a screw. A glue stick has a glue core on a lead screw from a knob at its end, so an old glue stick with the glue replaced by a ferrite ring makes a reasonable permeability tuned former. The coil is wound on its outside, and when assembled into an oscillator it gives a useful tuning range. This is hardly a new idea as permeability tuning could be found in car radios and TV tuners among other applications back in the day, but it’s still a good trick to bear in mind.
We’ve featured plenty of Bill’s videos before here at Hackaday, most recently tracking down an unusual early TV.