Here's an idea to try:
1. Place a trigger that is set to detect the presence of one side.
2. Name the trigger Radar.
3. Give it an x and y area in a circle as large as you'd like the radio detection to cover.
4. Set the trigger to activate repeatedly.
5. In the trigger's On Activation field, put the following code:
(list Radar) exec "radar.sqs"
6. Create the script, radar.sqs, and have the script do whatever you wanted to do, such as give a warning message, or whatnot.
You could have it count the number of enemy units, determine their direction from the radar station (or any other object), dispatch friendly units to the area, or whatever.