738 BELL SYSTEM TECHNICAL JOURNAL 



Fig. 2 (^) is a schematic circuit diagram emphasizing the land wire 

 sections to permit showing the locations of intermediate repeater 

 stations and terminal apparatus. This figure shows that the trans- 

 atlantic is similar to a long "four-wire" land telephone circuit in which 

 speech travels over different paths in the two directions. These two 

 branches are combined into a single circuit at the terminals where 

 special apparatus, including automatic switching devices, and specially 

 trained men known as "technical operators " are stationed. The usual 

 long distance girl operator establishes connections to subscribers. 



As will appear shortly, the duties of a technical operator have nothing 

 to do with the setting up of connections but require him to be continu- 

 ously attentive to the electrical operation of the circuit, and to make 

 adjustments of the amplification in the wire lines whenever the strength 

 of voice currents bound for the radio transmitter changes. He is 

 enabled to do this by watching the indicating needle of a sensitive 

 vacuum tube-operated meter, called a "volume indicator." The 

 volume indicator shows the strength or weakness of the electrical speech 

 waves in the line. Alongside of this meter are located the dials with 

 which he controls the amplification. Fig. 3 shows a technical operator 

 watching the meter at the New York terminal. The apparatus shown 

 on the panels in this picture includes the necessary terminal amplifiers 

 and devices for adjusting and maintaining various parts of the wire and 

 radio system. 



Fig. 2 {B) shows the relative strength of voice waves or "electrical 

 volumes" at various points in the circuit when a telephone subscriber 

 in England is talking to one in the United States. The broken lines in 

 this diagram indicate the magnitude of variations in the electrical 

 volumes delivered to the circuit and received from it, as well as trans- 

 mission variations in the radio section or "link." The relative values 

 of electrical volume in both directions of transmission are, of course, 

 essentially similar. The voice currents require about 1/15 of a second 

 to travel from either terminal to the other over the circuit. It is 

 interesting to consider that only about one fourth of this time is 

 occupied in traversing the radio link, although radio constitutes about 

 85 per cent of the total length of the circuit, the remainder being in the 

 wire lines and terminal apparatus. 



It is important to note from Fig. 2 {B) that the ratio of the strongest 

 to the weakest electrical volumes sent into the circuit at a terminal 

 may be as much as 1,000 times. This is indicated at (o) in the figure. 

 The variation is due partly to the different ways in which the sub- 

 scribers talk, and partly to the variation in losses in the lines which 

 connect the subscribers to the circuit. The technical operator adjusts 



