====== Amateur radio ======

Amateur radio combines communication, experimentation and learning. Operators use radio to make local and long-distance contacts, develop technical skills and explore propagation.

===== Frequency and wavelength =====

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.

===== What makes a contact? =====

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.

===== See also =====

  * [[:amateur_radio_band|Understand bands and propagation]].
  * [[:amateur_radio_operating|Learn how to make and log a contact]].
  * [[:glossary|Look up unfamiliar terms]].

===== Further reading =====

  * [[https://www.iaru.org/|International Amateur Radio Union]] — the international federation of amateur radio societies.