We find this circuit in American documentation from the 1980s. It consists of a frequency folder using a varicap. The capacitors and coils depend on the frequency of operation.
This interesting source, obtained in a 2001 catalog, can vary the output voltage between -16 and...
The LS4558 integrated circuit is a double 741. The filter response curve is given next to the...
This filter is from the Linear Applications Handbook of the National Semiconductor of 1994....