This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics magazine. The source must be symmetrical. The capacitors can be changed for other frequencies.
This excellent circuit came out in a Japanese publication from 1971. It uses Japanese transistors of the...
This circuit is a little more elaborate with the previous one (CB19402E). The operational...
This circuit was found in a 1994 documentation, but it can be easily assembled today, as it uses...