I just stumbled over the AM FM confusion as I started the TEW3 campaign again with the A-10C II. I think the easiest way to avoid this kind of confusion would be to give the modulation in mission briefing/kneeboard.
@baltic_dragon
I don't know how you manage it in your campaigns now, but I think it would be better to make sure the player has set correct frequency and only proceed if he has. If it's possible to set a flag in case the correct frequency is set I would do something like
If (frequency is set){
Play Mission Radio Call
}Else {
Play "Damn I got the wrong frequency" Message }
Just having no radio call and no message at all is a bad experience.