Demodulation is the reverse of modulation. The receiver extracts the information (audio or data) from the modulated carrier wave. For example, if frequency was modulated, the receiver tracks frequency changes; if amplitude was modulated, it tracks amplitude changes. Then that extracted signal is turned back into sound.
Depends on frequency and purpose:
Long wire / ferrite rod antennas for AM.
Dipole, monopole, telescopic antennas for FM.
More complex or directional antennas for ham, shortwave, or specialized use. Antennas are tuned to particular wavelength ranges for best reception.
You might get very weak or no signal without an antenna. Many radios have built‑in antennas (internal or telescopic) or expect to have external ones. The antenna picks up electromagnetic waves; without it, the receiver has little to work with.
Many sources: atmospheric effects (lightning, storms), electrical devices, power lines, nearby electronics, other stronger radio stations broadcasting on nearby frequencies, multipath reflections (signals bouncing off surfaces). FM is less sensitive to amplitude‑based interference; AM is more.
