Single side-band system applied to short waves

Although the single side-band system offers many advantages (increasing number of available channels, improving selectivity, giving less distortion and less trouble from fading, etc.) it has not yet been generally applied for shortwave work, although it is commonly used on long waves. The chief difficulty lies in supplying, at the receiving station, the suppressed carrier with sufficiently good synchronism. Synchronisation to at least 20 ~ is required, and on a wave-length of 15 m. This accuracy represents one part in one million. The necessary perfection can be secured either by the use of an accurately adjusted and reliable oscillator (e.g., a quartz oscillator) or by arranging a system of "pilot" signals. The author favours the latter, and discusses the possible systems in some detail, citing some successful tests made on the Buenos Aires-Madrid and the Madrid-Paris services.