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Stations have been monitored with female operators (live, or automated voice recordings) reading coded 5 - Letter groups.
These stations have been monitored since the mid -1970's.
Transmissions primarily appear to be one-way broadcasts and are usually identified with a tactical call-sign consisting of 3 phonetic letters (such as Charlie India Oscar. or Victor Lima Bravo, etc.). sometimes followed by a suffixed digit; the suffix "1" is indicative of a test transmission; a "2" means " no message." Broadcasts are often simulcast over several frequencies by a given call-sign. -
Originally posted by GrOuNd_ZeRo
the sounds are Number Stations.
Probably taken from The Conet Project.