Using the 741 this circuit can be adjusted to values between 1 Hz and 100 kHz. The power supply must be symmetrical. We found it in the Radio Electronics magazine of November 1973.
This line protector circuit was found in a 2002 documentation, but it is totally current and...
This antenna for the frequencies 146 or 440 MHz was found in a magazine 73 for Amateur Radio of...
With this circuit it is possible to increase the output voltage of a 7812 regulator. The circuit...