Coltano Signal Station, early 1960's (Source: Peter Byrne) Another part of the Technical Control area. In the bottom left hand corner are two chart recorders: EMT is monitoring the European Mediterranean Tropo system; ETA monitors the European Tropo-Army system. The EMT system was the Air Force system, part of the 486L MEDCOM system. The larger antennas (aka Billboard antennas) were the Air Force system, looking west towards Monte Vergine on Sardinia.