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.
Soldatensender Calais
"Soldatensender Calais" operated on the mediumwave band on 833 kHz (360 metres), 714 kHz (420 metres), and 612 kHz (490 metres), with an associated shortwave station "Kurzwellensender Atlantik" created to broadcast to U-boat crews. The station used a 500 kilowatt transmitter originally built for American broadcaster WJZ, in Newark, New Jersey. This transmitter had lain unused at the factory after the United States Federal Communications Commission imposed a 50 kW power limit on all U.S. stations, and so RCA was glad to sell it overseas and the British Secret Service bought it for £165,000. Codenamed Aspidistra, it was installed in a huge, underground bunker near Crowborough in Sussex, England, where it was briefly the world's largest medium wave station, perfect for deceptive "black" operation.