/diy/ - Do It Yourself

>>1704679
>>1704681
And a filter capacitor. In this case I'd be tempted to stick with a single-diode instead of a full-bridge, for ground reference reasons.

>>1704680
the springs would "short" the electric field, unless you made them out of plastic. Also pretty sure some primitive varicaps already work like this, though only with an offset spring-loaded metal plate as the top electrode held down by the screw that pulls it closer to the base with an insulator in between.

>>1704694
What matters more than absolute capacitance is the ratio between minimum and maximum capacitance, as it equals the maximum ratio of the highest to the lowest possible tuneable frequency. Furthermore, 400pF is actually pretty high for a variable capacitor, it's most common to get single plate models from 5-70pF, while decently-sized rotating multiplates get up into the ranges you're talking about.

>>1704717
>as you rotate the free end you add more loops and make the coil tighter
Sounds like copper fatigue in the making. Isn't it more conventional to just move a ferrite core in and out of a solenoid?