Abstract :
Receiver performance has in the past been limited by inadequate audio-frequency range (50¿5000 cycles per sec.) and inadequate range of volume levels. The paper describes a radio-gramophone in which alternative upper frequencylimits of 3, 5, 7, and 8 kilocycles per sec. are provided, and the range of volume levels is increased by including a form of ¿negative automatic volume control¿ in the audio-frequency amplifier. The first section of the paper summarizes the requirements of the new radio-gramophone, which include radio-frequency, intermediate-frequency, and audio-frequency circuits each of adjustable band width. The radio-frequency section includes amplified automatic volume control and a selective quiet tuning and indicating circuit. For gramophone reproduction a new pick-up and needle, with a cut-off frequency of 8000 cycles per sec, are described, together with a motor giving extreme constancy of speed. For the final acoustic reproduction, an improved electrodynamic loud-speaker is described having a paper cone with a metallic centre portion to give good reproduction up to 8000 cycles per sec. Circuit diagrams and performance characteristics of the individual sections of the receiver are illustrated, and the paper concludes with a series of acoustic frequency-response curves taken under various conditions.
