In the early twenties, began with amateurs assigned 200-250 m, i.e. 1500-1200 kHz.
Due to the increase of amateur licenses, in 1935 the relative density of stations per kilohertz on the air was over 8 times when compared with 10 years before. Thus, the familiar amateur bands 160-80-40-20 and 5 m had been assigned. This radio boom was due to the improvement in the transmitter technology by the elimination of several factors affecting the frequency stability for self-controlled oscillators.
The home wireless experiments era gave birth to the factory made equipments with many technological innovations responsible for so many advances in radio communication. Fig 291

Fig. 291 - Frequency allocation chart according the Washington convention in 1927.