FM broadcasting
VHF Radio waves do not travel far beyond the visual horizon, so reception distances for FM stations are usually limited to 30–40 miles (50–65 km) They can also be blocked by hills or buildings.
Radio 390
Radio 390 was named after the station's wavelength, so listeners would know where to tune. The actual wavelength was 388 metres (773 kHz), but 390 was easier to remember. Like its neighbour, Radio City, Radio 390 took advantage of the fort's layout by erecting a 250-foot vertical mast on an inner tower, guyed to three of the outer towers. This, with additional elevation from the height of the towers, gave a stable and efficient antenna, better than ship-based stations, ensuring coverage of southern England with only a 10 kilowatt transmitter. For advertisers, the station claimed 35 kilowatts.