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.
Indicated for powering circuits with operational amplifiers, this source was found in Popular...
This two-tone decoder has a bandwidth of 24%. The circuit is from a 1994 Electronics Now. The...
This circuit was obtained in the manual of the used integrated circuit. Equivalents may be used...