Take the most direct route to the Eastern Communications Post, sneak into the building marked by the Soviet flag on the roof via a hole in its rear wall, plant C4 on the radio transmitter, then leave without being detected. If you're quick, you can be in and out before guard patrols necessitate pauses or direct action. You can detonate the C4 charge from a safe distance, just before you exfiltrate the hot zone.

Simple method using grenade, like this clip, is also possible, but one of targets is difficult to aim.