Butterfly circuit
In the words of the patent application,
The principal object of the present invention is to provide ultra-high-frequency tuning apparatus which is readily tunable over a wide frequency range, and which avoids the difficulties of erratic operation encountered in some existing resonant circuit controls.
The arrangement consist of a butterfly-type capacitor (two sets of stator plates with a butterfly-shaped rotor that needs no electrical connections) within an annular (inductive) band that surrounds and supports the stators, forming parallel inductive paths between the stators. In effect, turning the rotor varies both the capacitance and the inductance of the tuned circuit, thereby allowing a large tuning ratio without requiring any sliding or wiping contacts.
Links
- US Patent 2,367,681, Ultra-High Frequency Tuning Apparatus. Eduard Karplus and Arnold P. G. Peterson. Filed 1941-12-10, Granted 1945-01-23
- GR Experimenter 1944, October issue describing the butterfly circuit