352 BELL SYSTEM TECHNICAL JOURNAL 



Volume Range 



Volume range to be transmitted without distortion or material 

 interference from extraneous line noise — about 40 db which 

 corresponds to an energy range of 10,000 to 1. 



Non-Linear and Phase Distortion 



Non-linear distortion with different current strengths and phase 

 distortion to be kept at such low values as to have negligible 

 effect on quality of transmission even on the very long circuits. 



The frequency range afforded by the new open-wire program circuits 

 extends about 3,000 cycles higher and more than 50 cycles lower than 

 the frequency range available with the open-wire ^ program circuits 

 previously used. The extension of the frequency range at the upper 

 end necessitates the sacrifice of one carrier telephone channel of carrier 

 systems operating on the same wires with the program pair since the 

 frequency band of the lowest carrier channel lies in this range. In 

 order to minimize noise and the possibility of crosstalk, the phantoms 

 of program pairs are not utilized and, of course, d.-c. telegraph com- 

 positing equipment is removed in order that the proper low-frequency 

 characteristics may be realized. 



Description of New Open-Wire System 

 In general, the amplifiers on the open-wire program circuits employ 

 the same spacing as the telephone message circuit repeaters on the 

 same pole lead. The average repeater spacing is about 150 miles 

 but the repeaters may be located as close as 60 miles or may be as 

 much, as 300 miles apart depending on the location of towns and cities 

 on the open-wire route and the gauge of the wires used. The upper 

 diagram of Fig. 1 shows a typical layout of the new wide-band open- 

 wire program system. Three types of stations are shown, a terminal 

 transmitting station, an intermediate station which may be either 

 bridging or non-bridging and a terminal receiving station. 



The terminal transmitting station includes an equalizer for correct- 

 ing for the attenuation distortion of the local loop from the broad- 

 casting studio, an attenuator for adjusting the transmission level 

 received from the local loop to the proper value, an amplifier for in- 

 serting the required gain, filters for separating the program and carrier 

 channels, monitoring amplifier, loudspeaker and volume indicator for 



^ A. B. Clark, "Wire Line Systems for National Broadcasting," presented before 

 the World P'ngineering Congress at Tokio, Japan, October, 1929; published in Proc. 

 L R. E., November, 1929, and in Bell Sys. Tech.^ Jour., January, 1930. F. A. 

 Cowan, "Telephone Circuits for Program Transmission," presented at Regional 

 Meeting of A. I. E. E., Dallas, Texas, May, 1929; published in Transactions of 

 A. L E. E., Vol. 48, No. 3, pages 1045-1049, July, 1929. 



