This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio Electronics magazine. Other operational amplifiers can be experimented, and the source must be dual.
The circuit was found in the February 1992 Radio Electronics magazine. The scale can be changed by...
Taiyo Yudem SAW filters can be ordered from Mouser Electronics for UMST (W-DMA), GSM, CDMA, LTE,...
This circuit was found in 1980s Electronic Engineering. Transistors can be modern equivalents. The...