Using the CA3140 integrated circuit, this switch was found in the June 1986 Radio Electronics magazine. Sensitivity adjustment is made at the trimpot in series with the sensor.
We found this oscillator in a documentation for radio amateurs from the 1970s. The circuit can use...
Many oscilloscopes have high impedance inputs that make it difficult to observe high frequency signals...
This is the receiver for the previous circuit we found in the December 1992 Radio Electronics...