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.
We found this circuit in an article in Electronics Now magazine from March 1996. The frequency is limited...
This circuit is designed to measure very weak currents, in the nanoampères range, using the 1 V...
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...