Radio Beacons During the 1930s to '50s most radio beacons in the waters around the coast of Sweden and many of its neighbors were made by AGA. These radio beacons were usually isotropic, i.e. the signal went out with the same strength in every direction. AGA also supplied directional radio beacons. These indicate a certain channel by radiating different signals on each side of the channel. AGA's first radio beacon equipment was completed in 1932. Intended for fully automatic operation is was designed to work analogously with the character of a lighthouse. The transmitter had low power so as not to disturb radio reception in the surrounding area. The intention was to provide an approach beacon and a range of 10 nautical miles was expected from the transmitter. The equipment was tested on board the lightship Grepen in the waters between Örskär and Öregrund in the Baltic Sea. During these tests the range was found to be double what had been expected. The beacon's new home was Visby harbor on the island of Gotland which is very difficult to approach in fog. In Visby an electric flashing apparatus was added to provide impulses. The beacon could be detected 70 nautical miles away which was considered a remarkably good result.