How callsign prefixes work
Every amateur callsign starts with a prefix that identifies the country that issued it. The International Telecommunication Union (ITU) gives each country one or more blocks of prefixes: the UK has G, M and 2, the US has K, N, W and part of A, and Australia has VK. Countries then share out their prefixes, so in the UK GM is Scotland and GW is Wales, and US call areas are numbered 0 to 9.
DXCC entities
For awards and contests, amateurs count DXCC entities rather than countries. The ARRL's DX Century Club list includes separate islands and territories that are far from their parent country, such as Alaska, Hawaii, the Canary Islands and Corsica, so there are about 340 current entities. Working 100 of them earns the DXCC award. This lookup uses the widely used country files maintained by Jim Reisert AD1C, which also include special prefixes and the exceptions for individual callsigns.
Portable and special callsigns
A callsign like F/G4ABC means a UK amateur operating in France, so the prefix before the slash decides the country. Suffixes such as /P, /M and /QRP don't change it. Special event and contest stations often use unusual prefixes, such as GB, which the lookup recognises too.
CQ and ITU zones
The world is divided into 40 CQ zones and 90 ITU zones, used in contest exchanges and for the WAZ (Worked All Zones) award. The UK is in CQ zone 14 and ITU zone 27.
Questions
What country is a VK callsign?
Australia. The digit after VK shows the state, such as VK2 for New South Wales and VK3 for Victoria.
What does DXCC mean?
The DX Century Club, the ARRL's award for contacting 100 or more of the roughly 340 DXCC entities.
What does F/G4ABC mean?
A UK amateur, G4ABC, operating in France. The prefix before the slash is the country they're operating from.
Which CQ zone is the UK in?
CQ zone 14 and ITU zone 27.