This resistive sensor was found in a 1969 US documentation. The circuit uses transistors of the time, but current equivalents can be employed.
This circuit can also operate with SW and even VHF signals up to 150 MHz. The circuit can be...
This integrating circuit multiplies the time that can be obtained with a 555 timer. We find it in...
This transmitter for the 7 MHz range, as we can assume by the number of turns of the coil, since the...