I moved this to Utility.
This is an EAM sent on the US military (USAF operated but used by all services) HF-GCS (High Frequency Global Communications System). 6739 kHz is one of their regular frequencies and you should hear these messages several times a day. By the way, although hobbyist are in the habit of calling all such coded messages "EAMs" they are not all EAMs. But, by design, you can't tell the EAMs from other types of messages, such as FDMs.
Frequencies used are 4724, 6712, 6739, 8992, 11175, 13200, and 15016 kHz.
"SEMI PRO" is a rotating callsign. In the past this network has variously used rotating calls, fixed calls of the base that originated the message, and MAINSAIL group callsign. Last year they shifted pretty much exclusively to the rotating calls, and have been using them for many months now.
T!