This circuit was found in the January 1989 issue of Radio Electronics magazine. The circuit sends audio signals by modulating a low-frequency carrier through the power grid.
The gain of the Operational Amplifier in the figure is given by the ratio between R1 and R2. In...
This circuit for the car can be found in other versions in this section. This is from an 80's...
This circuit was found in the December 1992 Radio Electronis magazine. R2 is an NTC, there is a...