THE NEW YORK-LONDON TELEPHONE CIRCUIT 745 



When the United States subscriber speaks, a small portion of his 

 voice currents enters a detector, operating relays TM and TES. The 

 action of relay TM causes the operation of relays 6'5 and CS, thus 

 clearing the outgoing line. The operation of relay TES short-circuits 

 the receiving line. The main part of the outgoing voice currents 

 passes on through the delay circuit, wire line and radio transmitter to 

 the distant subscriber. Any transmission picked up by the radio 

 receiver is blocked by relay TES. When the subscriber stops talking, 

 the relays are restored to the normal condition. 



While relays .SkS and TES are sufificient to switch the speech paths 

 back and forth and prevent singing, Fig. 5 shows that there are two 

 other relays which also interrupt undesired transmission. One of these 

 is relay RES, which operates when a subscriber in England is speaking 

 and short-circuits the United States transmitting line. This short- 

 circuit prevents the transmitting relays from being operated by the 

 echo of received currents returned from the local subscriber's line. 

 The other relay, shown in Fig. 5 as CS, is not used at present but was 

 needed when the circuit was first opened due to the fact that the radio 

 transmitter and receiver in the United States were much closer to- 

 gether than they now are. The action of relay CS is similar to that of 

 SS, but it was located at the radio transmitting station for an interest- 

 ing reason. Although the radio transmitter is of a type which should 

 radiate energy only during the actual transmission of speech, it would, 

 were it not for relay CS, put a certain amount of noise energy into the 

 air. While this noise, which originates partly in the radio transmitter 

 and partly in the wire lines connecting it to the terminal, is too weak 

 to be heard at the distant terminal, it was strong enough when picked 

 up by the radio receiver at Riverhead, Long Island, to interfere with 

 reception of the distant transmitter. Relay CS suppressed any such 

 noise when the transmitter was idle, that is, when no one was speaking 

 from New York. There are a number of ways of operating relay CS; 

 either by voice currents rectified at the radio transmitter or via a wire 

 circuit from the action set up by voice currents at the terminal. This 

 latter method is shown in Fig. 5. When the United States radio re- 

 ceiver was moved to Houlton, Maine, the use of relay CS was discon- 

 tinued, as the noise currents picked up there from Rocky Point were 

 negligible. 



A graphical representation of the time functions of two of the relays 

 on the transmitting side of the voice-operated device is shown in Fig. 6. 

 This illustrates the action during a representative spoken syllable. It 

 will be noted that relay SS does not operate at the exact beginning of 

 the speech. As shown at a in Fig. 6, it is necessary for the speech wave 



