THE NEW YORK-LONDON TELEPHONE CIRCUIT 747 



to build up to a certain definite amplitude before operation can begin. 

 After this a finite time a-b is required for the relay to operate. During 

 the interval from to h, the voice currents are passing through the 

 delay circuit. Thus the relay clears the path in time to transmit fully 

 all necessary parts of this speech wave e^^en though they have a very 

 weak beginning. 



The final trailing weak part of the speech wave is allowed to pass, 

 by making the 5'6' and CS relays release slowly by means of suitable 

 circuits not shown on the drawing. This effect is shown from g to li 

 in Fig. 6, as the "voice hangover" action. This action also functions 

 to hold relay SS operated during any momentary weak lapses of speech 

 between parts of the syllable as shown at e-f in the speech wave in 

 Fig. 6. 



As previously mentioned, a strong echo of the outgoing transmission 

 is picked up at the radio receiver and suppressed by relay TES, the 

 operation of which is indicated at c in Fig. 6. This echo is delayed an 

 amount represented hy to d in being transmitted over the wire cir- 

 cuits. Relay TES has a releasing time slower than that of relay 5'5' 

 by the amount h-j, which is sufftcient to care for the time that the echo 

 is delayed. 



In the operation of this system it is necessary for relays 5'5 and CS 

 and the devices which operate them to be sufftciently sensitive to 

 operate on all parts of the outgoing speech sounds in order that none 

 may be lost. On the other hand, relay RES need operate only on 

 impulses which, if allowed to be transmitted across the multi-winding 

 transformer ("hybrid" coil) as echoes, would be strong enough to 

 falsely operate the relays associated with the transmitting side. Use 

 of a relay on the receiving side which normally blocks reception would 

 be possible, but this would require very much greater sensitivity. Due 

 to the noise (static) introduced by the radio links, the use of such a 

 sensitive relay is undesirable. Therefore, the device has been made 

 to have a transmission path normally free in the direction in which the 

 noise is high and a normally blocked path in the direction in which only 

 the noise on the two-wire line need be combated. 



If it were not for the delay circuit on the transmitting side, it would 

 be necessary to increase the sensitivity of the voice-operated relay 

 device so that the relays would obtain enough current to cause their 

 operation at the very beginning of the speech wave, rather than allow 

 the wave to build up to an appreciable amplitude before operation 

 occurs. This delay circuit, therefore, permits appreciable reduction 

 in the sensitivity of the transmitting side of the device, reducing the 

 probability of operation by noise from the connected subscriber's line. 



