The Vodas * 



By S. B. WRIGHT 



Since the first transatlantic radio telephone circuit was opened 

 for service over ten years ago, an increasing number of voice- 

 operated switching devices has been added to the international 

 telephone network. All of these have the common purpose of 

 preventing echo and singing effects due to arranging the facilities 

 to give the best possible transmission, even under difficult radio 

 conditions. Differences in the design and performance of the 

 several types of devices suggest that the advantages and dis- 

 advantages of each be made available. 



The characteristics of two types of "vodas" used on circuits 

 connecting with the United States are described in this paper. 

 For reference purposes, a complete list of Bell System papers re- 

 lating to these devices is included. 



Introduction 



'TpHE interconnection of ordinary telephone systems by means of 

 -'- long radio-telephone links presents some unique and interesting 

 technical problems. Since radio noise is often severe as compared 

 with that in wire lines, radio transmitter power capacity is relatively 

 large and expensive, and it is in general economical to control the 

 speech volumes so that the radio transmitter will be fully loaded and 

 thus the effect of noise minimized for a given transmitter power rating. 

 This volume control, to be fully effective, calls for voice-operated 

 switching devices to suppress echoes and singing. 



This paper describes the measures which have been developed for use 

 at radio-wire junctions in the United States. They are based upon an 

 arrangement called a "vodas." This word, devised to fill a need for 

 verbal economy, is formed from the initial letters of the words "z;oice- 

 operated crevice anti-ringing"; and thus implies not only a suppressor 

 of feedback or singing, but also automatic operation by voice waves. 



The general principles and applications of the vodas have been 

 discussed from time to time in various papers listed at the end of this 

 text. The present paper goes somewhat more into detail regarding the 

 transmission performance of the vodas, including a description of an 

 improved form of circuit which discriminates between line noise and the 

 syllabic characteristics of speech. 



* Presented at the Pacific Coast Convention of A.I.E.E., Spokane, Washington, 

 September 2, 1937. Published in Elec. Engg., August, 1937. 



456 



