Found in 90s Popular Electronics, this circuit uses common general-purpose transistors in a configuration that has been extensively explored on this site and in our articles.
This simple transmitter can send signals to distances up to 200 m, depending on the power supply...
In the figure we have the original version of an amplifier with high input impedance, 1.2 M ohms....
This circuit powered by photovoltaic cells was found in the November 1998 issue of Electronics Now magazine....