With this circuit from the September 1989 issue of Radio Electronics magazine, it is possible to receive VLF band signals on a common radio, just like the signals emitted by the previous receiver.
This oscillator with crystal for overtone operation was found in an old American documentation. The coil...
In the figure we have a basic PLL circuit with the LM567 or equivalent. The circuit is from a 1977...
The A3906 integrated circuit from Allegro MicroSystems (www.allegro.com) consists of a single...