- (?:\d?[A-Z]{1,2}\d*/)? # out of area prefix /
- (?:\d?[A-Z]{1,2}\d+) # main prefix one (required)
- [A-Z]{1,5} # callsign letters (required)
+ (?:\d?[A-Z]{1,2}\d{0,2}/)? # out of area prefix /
+ (?:\d?[A-Z]{1,2}\d{1,5}) # main prefix one (required) - lengthened for special calls
+ [A-Z]{1,8} # callsign letters (required)