Diode is 1N60, or similar, 20 K ohm resistor is piezoelectric earphone or also known as Crystal earphone at 20 K ohm impedance. Metal stake driven into earth is ground connection.
Close to strong AM transmitter, body may be enough antenna. Longer pole or tree line length of aerial may be needed if weaker signal or distance from transmitter Apparently, adjust antenna length to receive best signal and be happy with getting strongest area signal is how it works.
Islanders tend to be less choosy as I learned in Santa Catalina, Key West, and Hawaii islands.
