INDtJCTlVE LOADING FOB TELEPHONE FACILITIES 197 



installation of H22 loading was planned for program facilities in a new ca- 

 ble between New York and Philadelphia. This loading had a 40% higher cut- 

 off frequency than the H44 loading previously mentioned, and a 30% 

 lower nominal impedance. It was expected that the program frequency-band 

 could be stretched to a 6000-cycle top. It used a new loading coil described 

 later on. 



13.2 B22 Program Facilities 



f While the preparation for the H22 trial installations was still under way, 

 further experimental and theoretical studies showed it would be desirable to 

 provide an equalized transmission-band from about 50 cycles to about 8000 

 cycles, so as to obtain a margin for probable future improvements in broad- 

 casting services. Accordingly, a decision was reached in September 1927 to 

 develop a new type of cable program facility that would be satisfactory 

 for lengths of 2000 miles or more. A new type of loading, designated B22 

 (22 mh loading coils at 3000-ft. spacing), was authorized and a trial in- 

 stallation on cable circuits looped back and forth between New York and 

 Pittsburgh was planned. 



The development of the new loading was only a small part of the total 

 development effort. The equalizing and temperature-regulation problems were 

 much more difficult than those previously encountered in the development 

 of long-distance telephone message facilities, partly because of the much 

 wider transmission-band and partly because of the more severe Hmits 

 necessarily imposed. Improved repeaters were required and crosstalk and 

 noise problems demanded very serious attention. A comprehensive account 

 of the development work and a detailed description of the B22 cable 

 program-facility is given in an A.I.E.E. paper^^ by Messrs. A. B. Clark 

 and C. W. Green. Accordingly, the remaining discussion herein is limited to 

 the loading. 



The theoretical cut-off frequency of B22 loading is a Uttle over 11,000 

 cycles; its nominal impedance is closely equal to that of H44 loading, previ- 

 ously mentioned. The theoretical nominal velocity of wave propagation is 

 about 20,000 miles per second. The use of phase equalization networks of 

 8 kc band width, however, slows down the actual velocity to about 13,000 

 mi/sec. The attenuation on 16 ga. pairs at average temperature is about 

 0.24 db/mi at 1000 cycles, and ranges from about .14 db/mi at 35 cycles to 

 about .38 db/mi at 8000 cycles. 



The new 22 mh non-phantom type loading coils used compressed, 

 permalloy-powder cores similar m size to those of the toll cable side circuit 

 and phantom loading coils previously described in general terms. Non- 

 linear distortion in the line was satisfactorily low m consequence of the 

 favorable hysteresis characteristics of the permalloy-core coils. 



