500kHz

500kHz refers to a specific radio frequency, 500 kilohertz. This frequency falls within the medium frequency (MF) band of the radio spectrum. Historically, 500kHz held significant importance in maritime communication. It was designated as the international distress and calling frequency for Morse code telegraphy. Ships and shore stations would monitor this frequency for emergency signals.

The use of 500kHz for Morse code distress calls was phased out with the adoption of more modern digital communication systems, particularly those employing GMDSS (Global Maritime Distress and Safety System). While its primary role as a distress frequency has diminished, the 500kHz frequency is still allocated for various purposes, including some forms of long-range radio navigation systems and certain amateur radio activities. The propagation characteristics at 500kHz allow for relatively long-distance communication, especially during nighttime hours, due to skywave propagation. Its historical significance as the international calling and distress channel for maritime safety is a key aspect of its recognition.