and a more ergonomic layout - the main on-air/DJ studio had a modern sound/mixing board, and a smaller one for the hourly news bulletins, production (of commercials, etc.) and as backup. Radio London's transmitter was housed in a large purpose-built steel shed on the rear deck, because it was too large to fit in the hold. The US-manufactured RCA Ampliphase transmitter was rated at 50,000 watts (50kW). An on-air slogan ran 'Your 50,000-watt Tower of Power', although initially it operated at 17kW. In contrast, Radio Caroline, its main rival, operated with a Continental Electronics 10kW transmitter. In 1966, Caroline South upgraded to a 50kW Continental transmitter and, for a time, Radio London pretended to retaliate by increasing its power to 75kW. The station's antenna was a vertical-guyed tubular steel mast aft of the bridge. Radio London's publicity claimed the mast was high, but later calculations from photographs indicated that it was approximately , . The positioning of the antenna was at the ship's centre of gravity and that was critical, as no cement ballast was used in the ship's hull to counteract movement caused by such a tall and heavy mast on a floating vessel. Although the wavelength was announced as "266 metres", the station experimented with frequencies between and , and tended to suffer night-time heterodyne interference from stations in Zagreb and elsewhere. In 1966, a number of test transmissions took place on , announced as "277 metres", using a 10kW standby transmitter, but it was decided not to change frequency on a permanent basis. After Radio Caroline South increased power and changed its frequency to in the spring of 1966, it caused some interference to Radio London on . That seems to have been caused by resonance between the two ships' antenna masts, and possibly by the Galaxys steel hull. Station closedown At midnight on 14 August 1967, the Marine, etc., Broadcasting (Offences) Act came into effect in the United Kingdom. It created a criminal offence of supplying music, commentary, advertising, fuel, food, water or other assistance except for life-saving, to any ship, offshore structure such as a former WWII fort, or flying platform such as an aircraft used for broadcasting without a licence from the regulatory authority in the UK. Despite initial plans to the contrary, Radio London decided not to defy the law, and closed before the Act came into effect. It was decided to close