Radioaaltoista

radioaaltoista, or radio waves, are a form of electromagnetic radiation whose wavelengths extend from about one meter to one thousand kilometres and whose frequencies range from 30 kHz to 300 GHz. They constitute the lowest‑frequency segment of the electromagnetic spectrum and lie above the microwave and far‑infrared regions.

The spectrum of radio waves is traditionally divided into several bands: extremely low frequency (ELF), very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra‑high frequency (UHF), super‑high frequency (SHF), and millimetre wave (MMW). Each band is associated with particular propagation characteristics and common technological applications.

Radio waves are generated by accelerating charges, typically in antennas or electronic circuits. The radiation can be linearly or circularly polarized, depending on the antenna geometry. The emitted field propagates as a transverse electromagnetic wave, with electric and magnetic components perpendicular to the direction of travel and to each other.

Propagation mechanisms vary across the spectrum. Low‑frequency waves diffract around the Earth’s curvature and can penetrate seawater and the ground, making them useful for submarine communication. High‑frequency waves reflect off the ionosphere, enabling long‑distance radio telegraphy. Very high‑frequency and higher bands propagate primarily in straight line (line‑of‑sight) and are employed for broadcast television, mobile communications, and radar.

Practical uses of radio waves include radio and television broadcasting, wireless networking, satellite communication, radar, medical imaging, and microwave ovens. The first man‑made radio signal was transmitted in 1895 by Heinrich Hertz, building on wireless concepts that led to modern telecommunications and the Global Positioning System.

Detection of radio waves is performed with antennas that convert the electromagnetic field into electrical signals, which are then amplified and processed by receivers.