- Crystals-The first radio receivers were based on the use of crystals, such as galena (lead sulfide) or silicon, to detect radio waves. These crystals had the property of rectifying alternating current, which meant that they could convert the high-frequency alternating current (AC) radio waves into a low-frequency AC signal that could be amplified.
- Coils-Coils of wire were used to form inductors, which are used to store electrical energy. Inductors were used in combination with capacitors to form resonant circuits, which were tuned to the frequency of the desired radio station.
- Capacitors-Capacitors are used to store electrical charge. They were used in combination with inductors to form resonant circuits, and they were also used to block DC current from flowing through the radio receiver.
- Batteries-Batteries were used to provide the electrical power for the radio receiver. Early radio receivers used wet-cell batteries, which consisted of a glass jar filled with an electrolyte solution and two metal electrodes.
- Antennas-Antennas were used to receive radio waves. Early radio receivers used long-wire antennas, which were simply lengths of wire strung up in the air.
- Earphones-Earphones were used to listen to the radio. Early earphones consisted of a pair of small speakers that were held against the ears.
- Vacuum tubes-Vacuum tubes were later developed as a more efficient way to detect and amplify radio waves. They replaced crystals as the main active components in radio receivers and transmitters.