This interference rejection circuit for telegraphy was found in a 1980s documentation for radio amateurs. The integrated circuits used are common today.
This 80's Motorola circuit can generate 100 MHz signals, but they can reach 200 MHz with the...
Of course, the current is extremely small, but a voltage of 300 V can be obtained from 9 V of a...
We found this solid-state relay circuit that can function as a shield in a Radio Electronics...