This weekend I made a variable inductor for an antenna tuner from a double pole, 6 position switch, a T80-6 toriod, some 26 gauge wire, and a lot of patience.
To begin I had to modify the switch to make it a single pole 12 position switch. I removed a set of contacts and bent the internal switch stop. This allowed 12 independent positions and 360 degree rotation.
Next I had to calculate the desired impedance for each switch position. I started with .25uH in the first position and increased the uH for each additional position. By the 12th position it will have 11.25uH of inductance.
Winding the toriod was a challenge because of needing 50 turns with 12 taps on it.
Then came the daunting task of soldering each tap from the toroid to the switch.
I could have made a larger inductor from a coil of wire and used a movable tap, but this is intended for a QRP tuner handling less than 5 watts of output.
Until next time....
