These are the purest form of radio, requiring no batteries or external power. They work by "harvesting" the energy of the radio waves themselves.
Uses a movable ferrite core instead of a variable capacitor to change stations. 2. AM and Shortwave Receivers Radio Receiver Projects You Can Build By Homer L Davidson
These projects utilize modern (at the time) integrated circuits like the LM386 audio amplifier to drive speakers rather than just headphones. These are the purest form of radio, requiring