A NEW TELEPHOTOGRAPH SYSTEM 561 



All of these outputs terminate in high impedance circuits and have no 

 appreciable reaction upon the constancy of operation of the fork. 



Line Facilities Used with the New Telephotograph Equipment 

 Requirements for the communication channel used in the trans- 

 mission of pictures are obviously dependent upon the characteristics 

 of the telephotograph equipment employed and the amount of de- 

 gradation resulting from transmission which can be tolerated. In 

 general, telephotograph equipment capable of recording the trans- 

 mitted signals with a degree of fidelity of the order required for good 

 pictures may also record certain extraneous disturbances in the 

 transmission channel which will appear as blemishes on the received 

 picture. The more important of these disturbances are abrupt 

 variations in line net loss, delay distortion, certain types of noise, 

 echoes, and crosstalk. With the exception of delay distortion which 

 is more pronounced for the new equipment because of its higher speed 

 of transmission, the requirements relating to the other disturbances 

 are comparable to those applying to the earlier Bell System equipment. 

 Experience over a period of years with the earlier equipment indicated 

 that selected telephone circuits, specially conditioned to adapt them 

 to picture transmission and established as a regular network, could 

 be relied upon to give consistently good results. This general pro- 

 cedure has been followed in establishing wire networks for use with 

 the new telephotograph equipment and unretouched reproductions of 

 typical news pictures received over such circuits are shown in Figs. 8 

 and 11. 



The circuit facilities employed with the new telephotograph system 

 are 4- wire H-44-25 side circuits in cable ^^ where available and elsewhere 

 2-wire open-wire " side and physical circuits.* These facilities are 

 provided with delay equalizer networks for the frequency range from 

 1,200 to 2,600 cycles per second and precautions are taken to minimize 

 various transmission disturbances. Means are provided, controlled 

 by the sending telephotograph equipment, to prevent operation of the 

 transmission regulating network relays on cable circuits during the 

 transmission of a picture, and to obtain one-way transmission over 

 2-wire circuits. A wire network of nearly 8,000 miles established as 

 outlined above and connecting 26 stations of the new telephotograph 

 equipment has been in operation for more than a year, giving reliable 

 and technically satisfactory service. 



* A side circuit is a physical circuit that is used for one of the paths of a phantom 

 circuit; the notation H-44-25 indicates a loading coil spacing of 6,000 feet, inductance 

 of physical or side circuit loading coils 44 millihenries, and inductance of phantom 

 circuit loading coils 25 millihenries. 



