Hi..
I am a bit noob myself. But i think you put this in your init.sqs file (in the user/mission folder) The init file contains everything your mission is going to contain or do in the start of it....
in the init.sqs: 1 setRadioMsg "null" (1 being radio alpha,2 is bravo......)
and you have: 1 setRadioMsg "message" in a trigger you like?
Maybe this is of some help.....
If this isnt helping you may wanna take a look at the tuturials....