Prefix allocation
The ITU prefix identifies each call sign worldwide — Switzerland was allocated the HBA–HBZ group in 1929; H9 became HB9.
ITU prefix
The ITU prefix (commonly known as the country code) is an internationally recognised component of the call sign of a transmitting installation or radio station, allocated by the International Telecommunication Union (ITU). The prefix is country-specific and serves to uniquely identify the call sign. It may consist of individual letters, digits or a combination of both.
The registration marks for aircraft in international aviation are also derived from this. The Latin alphabet and Arabic numerals are used.
In 1929, Switzerland was allocated the group HBA – HBZ (HB standing for ‘Helvetischer Bund’). The number 9 was allocated to amateur radio operators by the authorities — H9 became HB9.