: Often the first project, this design uses only an antenna, a tuning coil (inductor), a diode for detection, and earphones. It serves as a powerful demonstration of energy harvesting, as it operates entirely on the power of the received radio signal without external batteries. Regenerative Receivers

Moving beyond crystal sets, Davidson introduces active amplification to catch signals from further away.

: The quintessential beginner project. It requires no battery power, instead drawing energy directly from the radio waves themselves. It’s a masterclass in tuning and antenna design.