Abstracts of Technical Articles by Bell System Authors (01 April 1949)

Electrons and the crystal trap density. Experiments are described which lead to a hypothesis of space charge neutralization. A possible cause of the current fluctuations observed at high crystal fields is discussed. The Philosophy of PCM * B . M . OLIVER, J . R . PIERCE and C . E . SHAN- NON. Recent papers describe experiments in transmitting speech by P C M (pulse code modulation). This paper shows in a general way some of the advantages of P C M , and distinguishes between what can be achieved with P C M and with other broadband systems, such as large-index F M . The intent is to explain the various points simply, rather than to elaborate them in detail. The paper is for those who want to find out about P C M rather t h a n for those who want to design a system. Many important factors will arise in the design of a system which are not considered in this paper. 

Objectives for Sound Portrayal.6 RALPH K. POTTER. Translation of sound into visible patterns is discussed in terms of broad objectives. It is suggested that no single design can be optimum and that perhaps the most useful standard of reference is the human ear. Special interests and complexity generally affect final design requirements. A Waveguide Bridge for Measuring Gain at 4000 Mc.6 A. L. SAMUEL and C. F. CRANDELL. A bridge has been constructed for measuring the gain and phase delay of amplifiers in the vicinity of 4000 Mc. The equipment is described, and the methods employed to reduce the possible errors are discussed.