In order to meet future demands for high‐grade and economical circuits in cables, considerable carrier development work has been done which has included an extensive experimental installation on a 25‐mile loop of underground cable. Sufficient pairs were provided in the cable and repeaters were installed to set up nine carrier telephone circuits 850 miles long. Tests on these circuits showed the quality of transmission to be satisfactory, while the methods and devices adopted to prevent interference between them were found to be adequate. The trial has, therefore, demonstrated that the obtaining of large numbers of carrier telephone circuits from cable is a practicable proposition. This paper is largely devoted to a description of the trial installation and an account of the experimental work which has been done in this connection. Due to present business conditions, it is expected that this method will not have immediate commercial application. This work is part of a general investigation of transmission systems which are characterized by the fact that each electrical path transmits a broad band of frequencies. Such systems offer important possibilities of economy particularly for routes carrying heavy traffic. The conducting circuit is non‐loaded so that the velocity of transmission is much higher than present voice‐frequency loaded cable circuits. This is particularly important for very long circuits where transmission delays tend to introduce serious difficulties.

No abstract

Svxoesrs: The application of telephone repeaters has made it possible to use small gauge cable circuits to handle long distance telephone service over distances up to and exceeding 1,000 miles. A general picture of the long toll cable system which is being projected for usc in the northeastern section of the United States was presented recently by Mr. Pilliod and published in the July number of the Technical Journal.Many of the Circuits in these toll cables are so long electrically that a number of effects, which are comparatively unimportant in ordinary telephone circuits, become of large and sometimes controlling importance. For example, the time required for voice energy to traverse the circuits becomes very appreciable so that reflections of the energy may produce "echo" effects very similar to echoes of sound. The behavior of the circuits under transient impulses, even when two-way operation is not involved so that "echoes" are not experienced, is very imp?rtant. In order to keep within proper limits of variation of efficiency With frequency over the telephone range special corrective measures are necessary. Owing to the small sizes of the conductors, the attenuations in the longer circuits arc very large. Special methods are, therefore. required to maintain the necessary stability of the transmission, including automatic means for adjustment of the repeater gains to compensate for changes in the resistance of the conductors caused by temperature changes.

In a recent paper amplifiers capable of handling frequency band widths of the order of 1,000 kc. or more are described, together with terminal apparatus for effectively utilizing these wide bands for telephone, telegraph and television purposes. The paper confines itself to the coaxial line structure for transmitting these wide frequency ranges but points out that broad‐band transmission is also applicable to balanced conductor systems. The present paper discusses briefly some of the possibilities of the more familiar balanced circuits, circuits more or less as they now exist in the present plant being first considered, following which are circuits obtained by new construction. Wide‐band transmission over balanced circuits offers interesting possibilities both for circuits in the present plant and for new construction.

No abstract