I'm not sure if I'm clear on what you want to happen here, but here's a possible solution...
You could accomplish what I
think you're after with a couple of triggers....
Radio TriggerSize:
as requiredCondition: Radio Alpha
Text: null
<-- Note: TEXT field, not name fieldCondition field: this
OnActivation field:
as requiredRadio on/off TriggerSize: 0,0
Condition: none (repeatedly)
Condition field:
unit in
vehicleOnActivation Field: 1 setradiomsg "
Radio call's name"
OnDeactivation Field: 1 setradiomsg "null"
So the first trigger is your radio message. Make it how you like it, just make sure the
Text field has
null in it... this way the radio call won't show up.
The second trigger detects when
unit (I'm guessing you'll want to put the player in there) is in
vehicle (again, put the name of your vehicle in). When this happens, it sets the radio message to the text in the quotes.
If
unit gets out, it sets the radio message to nothing again (so the player can't use it).
Anyway, as I said I'm not sure if I've read the situation you want correctly here. It's quite easy to adjust it for
any vehicle rather than a specific one, but if you give us a bit more info we'll tailor something a bit more specific to your needs