Radio triggers are like global variables and even more confusing. They exist on all machines (east, west, etc..). The values that set them off (i.e. Radio Alpha) are not only global, but are broadcast to all machines.... (one of the few values that are automatically broadcast). So... if you click Radio Alpha, the trigger goes off on all machines. If you wish to limit it to a specific side, you must make this your Condition line:
(this) AND (side player==WEST)
this makes it so that not only the radio alpha is pressed (the "this") but also that the player is a WEST unit (the "side player==WEST")
the only thing to look out for is that all players on WEST will have it triggered, so... if it is something that only needs to run once (take for example a script that creates a Tank) you must further refine you activation line or script in something to make sure it only runs once.
For example:
three players on West side... and player one clicks a radio alpha that calls a script "makeTank.sqs"
Three Tanks would appear because the other two players machines would act as if Radio Alpha was also pressed on their machines because not only is Radio Alpha true... but they are WEST units also.
er... I hope this isn't too confusing for ya