Transmission Features of the New Telephone Sets

The new telephone instruments now being introduced by the Bell System result in an outstanding improvement in transmission performance in service. The evidence for this, as obtained by comprehensive laboratory and field tests, is presented here together with a discussion of the factors responsible for this superior performance and of the consideration involved in its appraisal. being in the plant of NEW telephonetoinstruments are wallsetappliedhandset, and resultthe Bell System the deskstand, and in markedly improved transmission performance. The new instruments are associated with the anti-sidetone feature which is also applied to the older sets already in plant. The selection of these particular designs from the wide choice made possible by new design technique, materials and manufacturing methods, has been based on developments in the methods for quantitatively rating the relative merits of different designs. In general there has been consistent effort over a period of years to base these ratings primarily on performance in service rather than on laboratory tests. The factors influencing service performance are so many, and so complicated in their relationship, and are in so many cases difficult or even impossible for the designer to evaluate or control, that their net effect on performance cannot be predicted with certainty by laboratory methods. Of necessity such methods involve a limited selection of primary test conditions, and an even more limited selection from the possible combination of these conditions.