On this page of our guide to Sniper Elite 4 you will find out how to murder an enemy radio operator as part of the second mission of the game - Bitanti Village. Getting rid of this opponent is not a mandatory mission objective, although you can easily earn a lot of experience points by completing it.
It's best to combine this side objective with retrieving the report of the assassinated sniper. Once you have the report, exit the tower and approach the bridge (M2.5): you will be able to spot a window, at which the operator spends most of his time (M2.2). He will leave his building from time to time, so if you don't spot him right away, just wait for a while. You won't have any problems with recognizing him - he has a large radio on his back.
The wind should not cause much of a problems so taking him out should be easy (about 120m). You could also come a little closer and adjust the weapon to 100m.