622 BELL SYSTEM TECHNICAL JOURNAL 



transformers providing adequate transmission of the entire frequency 

 range from 10 cycles to 20,000 cycles. 



Arrangements for Television Circuits 



Line Layout between New York and Washington. The layout of 

 the wires between New York and Washington is shown in Fig. 2. 

 The circuit over which the waves actually carrying the pictures were 

 transmitted (marked Picture Circuit) consisted principally of a pair 

 of copper wires 165 mils in diameter. At a number of places on the 

 route the circuits were carried in cable as indicated in the figure. 

 The total length of the television circuits was about 285 miles, of 

 which 8 miles consisted of cables and the remainder of open wire. 



Transpositions. As the circuits employed were originally designed 

 for voice-frequency operation only, except for a section at the New 

 York end, it was necessary to add transpositions to them to prevent 

 interaction with adjacent circuits at the high frequencies involved in 

 the television transmission. The high-frequency currents were thus 

 prevented from passing over into the adjacent circuits which would 

 have resulted in irregularities in the attenuation, line impedance and 

 phase shift characteristics of the circuit. 



Incidental Cables — Loading. Any appreciable length of non-loaded 

 cable included in an open-wire television circuit has certain very 

 objectionable effects. The impedance irregularities introduced by the 

 cable destroy the uniformity of the line attenuation, impedance and 

 phase shift characteristics as a function of frequency, and tend to 

 produce echoes as described above. Types of loading developed 

 for use on incidental cables occurring in circuits employed for carrier 

 telephone and carrier telegraphy operation - were employed to reduce 

 these effects to a minimum. This carrier loading is designed so that 

 when used on No. 13 A. W. G. cable circuits it provides an impedance 

 which approximates very closely that of the open wire. With a 

 spacing of about 930 feet between loading coils, this loading has a 

 nominal cut-off of about 45,000 cycles, which corresponds to an 

 effective transmission range extending up to about 36,000 cycles. 

 In order to obtain a close match between the impedances of the open- 

 wire and the cable pairs, thereby avoiding impedance irregularities, 

 13-gage pairs were selected for the television circuits in all of the 

 cables. 



The length of the submarine cable under the Hackensack River 

 (about 1100 feet) was too great to permit the use of regular carrier 



^ "Development and Application of Loading for Telephone Circuits," T. Shaw 

 and W. Fondiller, Journal A. I. E. E., Vol. XLV, pages 253-263, March, 1926. 



