Asymmetric side-band broadcast transmission

Abstract

Wireless broadcasting technique is hampered because of the scarcity of channels and the multiplicity of transmitting stations. The spectra of frequencies radiated by stations occupying frequency-contiguous channels overlap, and the audio-frequency output from the receiver which is designed for ordinary domestic reception must be limited to meet the existing conditions of transmission. It is improbable that European nations will agree to limit either the existing power or the number of working stations; but, if it were possible to modify transmitters so that the spectrum of frequencies radiated contained the carrier and only one set of side-bands, spectrum overlap would be avoided or minimized.The paper sets out suggestions for limiting the frequency band-width of transmission by methods which are neither elaborate nor costly and which could be easily incorporated in existing transmitter circuits. It is shown also, that the adoption of the suggested technique would not cause service dislocation. A quantitative analysis indicates that, although the proposed adaptations do not limit the transmitted spectrum to a band width containing only the carrier and one set of side-bands, and although the transmission of certain vestigial side-bands is essential to the method, nevertheless, if the methods were adopted, spectrum overlap could be greatly minimized and transmission conditions would be more favourable to high-fidelity reception than they are to-day.