This circuit has an accuracy of 1%. The components used must be precision as well. The input frequency range is 40 Hz to 10 kHz with the indicated components.
The basis of this circuit is a CA3130 operational amplifier. The transistor can be BC548, and the...
This circuit, found in a 73 magazine for radio amateurs, is used in radio localization. The...
This circuit is from an American magazine Popular Electronics of March 1991. The circuit produces both...