The figure shows a remote-control receiver working the 27 MHz band, very popular in the 60’s. The circuit us from a February 1961 Radio Electronics magazine.
Found in American documentation from the 90's, this JFET stage has an input impedance of 500 M...
We found this circuit in a 1995 documentation. It can measure frequencies from 100 kHz to over 100 MHz...
This circuit was obtained in a documentation from the 70s. The operational amplifiers used are...