570 BRLL SYSTEM TECHNICAL JOURNAL 



Telephotograph Networks 



One of the obvious advantages of network operation of telephoto- 

 graph stations is that it offers a means for rapid and simultaneous 

 distribution of facsimile information and pictures to a large number of 

 receiving points. This method of operation appears to be particularly 

 advantageous for use by the large news-picture gathering and dis- 

 tributing agencies giving a nation-wide service. Such network opera- 

 tion of a number of telephotograph stations presents additional 

 requirements, not mentioned in the preceding paragraphs, which may 

 be of general interest. 



Requirements encountered in connecting a large number of sending 

 and receiving stations were that any sending station should be able 

 to transmit a picture simultaneously to all receiving stations, and 

 that any one station could be selected as the transmitting point, 

 establishing a new direction of transmission with a minimum loss of 

 time. The situation has been met by permanently bridging each 

 telephotograph station, consisting of separate sending and receiving 

 equipment, to the wire network on a 4-wire basis using separate 

 sending and receiving station loops and performing automatically such 

 switching operations as may be involved in altering the direction of 

 transmission. 



Typical arrangements which have been used at a bridging point on 

 a telephotograph network are illustrated in Fig. 14. Suppose, for 

 example, that the telephotograph station at this point wishes to 

 transmit a picture to the network. Operation of a key associated 

 with the subscriber's telephotograph transmitting equipment sends 

 out a d-c. signal over the simplexed loop to the control circuit station 

 repeater at the local telephone ofihce. Since this repeater is multipled 

 with the d-c. repeaters associated with each of the telephotograph 

 circuits connected at this point, the signal is transmitted over the 

 entire network and the switching operations performed to place the 

 circuits in condition to send a picture from this point. The d-c. 

 repeaters at the local telephone ofifice also cause short circuits to be 

 applied to the incoming transmission paths which are connected to 

 the bridging networks, thus preventing the temporarily inactive parts 

 of the circuit from contributing possible disturbances to the outgoing 

 paths being used. This figure also indicates the switching operations 

 performed on the 4-wire terminating set. At the conclusion of the 

 transmission the d-c. control circuit is automatically released by the 

 transmitting machine and the circuits returned to the initial two-way 

 condition permitting any station on the network to seize control of 

 the circuits for picture transmission. Signal lamps are provided at 



