Amateur radio combines communication, experimentation and learning. Operators use radio to make local and long-distance contacts, develop technical skills and explore propagation.
Frequency describes how quickly a signal oscillates and is measured in hertz (Hz). Common units are kHz, MHz and GHz. Wavelength describes the distance occupied by one cycle of the wave.
In free space, a useful approximation is:
wavelength in metres = 300 / frequency in MHz
This connects band names to frequency. Antenna dimensions also depend on their design, materials and surroundings; the free-space wavelength is a starting point rather than a finished construction plan.
A radio contact, often called a QSO, involves stations exchanging information over the air. A callsign identifies a licensed station or operator. The operating mode determines how information is carried: voice, Morse code and digital data are familiar examples.