WW2 Beam systems
Standard Beam Approach was the UK implementation of the German Lorenz Beam Approach system.
SBA was installed at a large number of UK airfields and, despite a crazy amount of investment in money and time, was almost a complete failure, being rejected by Coastal Command in 1941, and by Bomber Command in 1943. It was unreliable and unstable, and was eventually replaced by BABS and Lucero.
The early version of SBA had 'dots to the left' and 'dashes to the right'. Later (1942ish ?) this became Morse A/N coding as described. It was reckoned to be more readable.
SBA was far too bulky for single seat aircraft, hence in 1941 a system was developed to allow these aircraft to use their existing VHF R/T sets. It was named VHF or Tuneable BA and was significantly better than SBA.