Sound Transmission from London Television Station

Abstract

IT is well known that the use of ultra-short wavelengths for broadcasting purposes facilitates the attainment of a very high quality in the sound transmission on account of the extensive range of side-band frequencies which may be employed. At a meeting of the Wireless Section of the Institution of Electrical Engineers on May 3, Messrs. I. L. Turn-bull and H. A. M. Clark read a paper on “The Marconi-E.M.I. Audio-Frequency Equipment at the London Television Station”. This paper outlines the requirements of a high-quality sound equipment and describes the design and constructional features of the Alexandra Palace installation. The final section of the paper gives information on the overall performance of the apparatus and includes data on the frequency and harmonic distortion of the amplifier equipment. The overall frequency response from the microphone to the modulated radio frequency output to the transmitter is practically uniform from 40 cycles per second to more than 10,000 cycles per second; the second harmonic content varies up to a maximum of 0-5 per cent for full (that is, 100 per cent) modulation, while at the same modulation level the third harmonic content is about 0-1 per cent. The authors express the opinion that it is this low odd-harmonic distortion, quite as much as the extended frequency range, that is responsible for the satisfying and pleasing quality of the sound transmitted. The equipment has been in operation for a period of two years with complete satisfaction. It may be remarked in conclusion that, for some time past, it has been the practice of the British Broadcasting Corporation to transmit part of the ordinary National or Regional programme through the Alexandra Palace ‘sound’ transmitter, so that listeners having a television or other suitable ultra-short wave receiver may take advantage of this high-quality broadcasting station.