-# check that a field only has callsign characters in it but has more than the standard 3 callsign letters
-sub is_long_callsign
-{
- return $_[0] =~ m!^(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+) # basic prefix
- (?:/(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+))? # / another one (possibly)
- [A-Z]{1,5} # callsign letters
- (?:/(?:[A-Z]{1,2}\d+ | \d[A-Z]{1,2}\d+))? # / another prefix possibly
- (?:/[0-9A-Z]{1,2})? # /0-9A-Z+ possibly
- (?:-\d{1,2})? # - nn possibly
- $!x;