Before the beginning of the First World War, the vast majority of them were spark And therefore could be used only in the telegraphic mode and almost exclusively by state structures, post, communications and military and in very rare cases - by lonely radio enthusiasts In 1903, the Danish engineer Waldemar Poulsen invented the arc transmitter, which was essentially a type of spark transmitter But instead of a single spark discharge, he used a series of discharges that created an arc It was the first type of transmitter that managed to generate continuous sinusoidal signals and not shaky as in spark transmitters However, almost at the same time, in 1902, the Canadian Reginald Fessenden patents another type of radio transmitter - a machine generator-alternator With the help of the latter, he managed to overtake Marconi in terms of transmission range and the first in the world in 1906 to achieve stable bilateral communication between the USA and Great Britain and this was the distance record at the time But the most important for radio broadcasting was his other patent - "Apparatus for sound transmission using electromagnetic waves".