This can be put in the Init.sqs of your mission, or in a trigger. Targetfound.sqs is what happens when a target is located, you might want put in the script:
[West,"hq"] sidechat "We've found a tank at DF25"
_unit = your chopper
_target = an enemy unit like a tank or uaz
the targetfound.sqs would look a little like this:
_unit = _this select 0
_unit sidechat "blablabla"
~2
[West,"hq"] sidechat "blablabla"
exit