Abstract: A field unit for warning of a danger of collision between an aircraft and an obstacle, in particular a topographical ground obstacle or an obstacle formed by a mast, building or aerial cable structure, comprises a multi-part tubular mast having devices for fixing a solar panel and a radar antenna; an elongate radar antenna in an environment-protective casing, which, with an electronics unit, forms a radar system for synthesized radar detection of an aircraft in a radar coverage area; a central processing unit for identifying on the basis of information from the radar system an aircraft which is in a zone of the radar coverage area and which on the basis of radar information such as direction, distance and/or speed computes a collision danger area; and a high-intensity light system and radio transmitter system that can be activated by the central processing unit upon detection of an aircraft in a collision danger area.