Single Wire Communications System
Here is a tone oscillator which uses two Transistors in a circuit which can power an Earphone connected at the other end of a single line a long distance away. A single line is all that is needed because the ground may be used as the second conductor.
The tone is composed of pulses which have a fundamental repetition rate of about 1600 cycles per second (hertz). This may be used to send code messages to a friend who is at the opposite end of the yard.
For the wire, you can use a fence or a clothes line, or any other metallic conductor. The ground connection can be made by connecting to some already grounded metallic object or something metallic pushed into the ground. Here is where some 'grassroots' experimenting can be done!
The oscillator circuit is arranged like a push/pull amplifier. The difference, of course, is mainly that the output across the Transformer is connected back into the input (base circuits) through the Capacitors. The amount of bias current supplied to the bases is quite high to obtain the strong oscillations.
You can experiment with this circuit by changing Capacitor and Resistor values, but don't decrease the values of Resistors or the Transistors may be damaged.
It is also interesting to place the Resistor directly across the Capacitors instead of from Battery negative to one end of a Capacitor.
Try different size Capacitors with these connections. With this circuit it is possible to obtain nearly every type of signal, from a sine wave to a square wave to a narrow pulse wave. If you have a VOM you will want to measure total Battery current as you experiment with this circuit.
Place the Meter on a current range above about 15mA, and then insert the Meter in series with the Key. Will this circuit work on 3 volts? Try it.
You are generally safe when trying lower voltages for Transistor circuits. About the only time a lower voltage may not be safe is when a motor is involved.