This third-order Butterworth filter was found in American documentation from the 1980s. Formulas for component calculations are attached to the diagram.
Found in a Popular Electronics from the 1990s, this circuit uses components from National...
This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the...
Suggested by the 90s ARRL Handbook edition, this circuit aims to reduce or cancel noise at the...