We found this circuit in an old Mullard (Philips) documentation. The sensor consists of a reed-switch that is coupled to a magnet on one of the wheels of the vehicle.
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...