THE OCCURRENCE AND EFFECT OF LOCKOUT 263 



curred and Ks resumption operates he before W's response can operate 

 hj , a second lockout which will be of the lasting type, will at once occur. 

 Otherwise W's response will operate hJ giving control of the circuit 

 to W. 



Experimental Conditions and Data 



To obtain experimental data of the occurrence of lockout in long 

 distance conversations and to determine the resulting effect on repeti- 

 tion rate, added delay and echo suppressors were inserted at the New 

 York end of a circuit to Chicago, Illinois. This circuit is used as a 

 tie line by the Western Electric Company for the transaction of com- 

 pany business between its Hawthorne plant and New York office. 

 The regular echo suppressor usually associated with the circuit at 

 Pittsburgh was removed for these tests. The circuit arrangement em- 

 ployed is shown schematically in Fig. 2, the added equipment being in- 

 cluded between the dotted lines. This equipment was adjusted to have 

 zero insertion loss and the frequency characteristic was equalized to 

 within ± 2 db from 200 to 3000 cycles. The overall net loss from toll 

 board to toll board was 7 db. The suppressors were 44-A echo sup- 

 pressors operating at a sensitivity of 31 db referred to the zero level 

 point of the circuit, except in those cases specifically mentioned. The 

 added delay circuits were of the acoustic type consisting essentially of a 

 suitable length of brass pipe terminated by high quality loud speaking 

 telephones together with the necessary amplifiers and equalizers to give 

 zero loss over the frequency range from 200 to 3000 cycles. These de- 

 lay circuits were available in units of 0.023, 0.05, 0.08, 0.10 and 0.15 

 second, and various combinations of these delays were used together 

 with the tie line delay of 0.043 second to obtain the circuit conditions 

 which were tested. 



The details of the recording mechanism are indicated schematically 

 in Fig. 2. A relay was added in series with the shorting relay of each 

 echo suppressor, so that every operation of the echo suppressor relay 

 was accompanied by an operation of the added relay. The simultane- 

 ous operation of these relays energized two other relays, one of which 

 in turn operated a message register to record the number of lockouts, 

 and the other connected a 20-cycle oscillator to a cycle counter to record 

 the locked out time. 



Service observers at New York monitored both directions of the 

 conversation and recorded repetitions and other pertinent data regard- 

 ing each call. 



The circuit conditions tested are shown in Table I, the notation of 

 which corresponds to Fig. 1. For each condition the first line re- 



