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BELL SYSTEM TECHNICAL JOURNAL 



ciently broad frequency range be transmitted. As explained in an- 

 other paper 3 it is not sufficient that a telephone circuit transmit sus- 

 tained alternating currents within a given frequency range. It must 

 also transmit short pulses of alternating currents within the proper 

 frequency range without introducing oscillations of its own or "tran- 

 sient effects." This requires that loaded circuits for loud speaker use 

 have a high cut-off frequency and hence have the frequencies of the 

 predominant natural oscillations high. It has been found that when 

 the cut-off frequency of loaded circuits is about 5000 cycles, good 

 results are secured with loud speakers. 



The two types of telephone circuit which best meet the require- 

 ments of transmitting a broad band of frequencies, both when sus- 

 tained and when applied in short pulses, are non-loaded open-wire 

 lines and extra-light loaded cable circuits. These are suitable for 

 transmission over very long distances. For transmission over short 



1000 1500 2000 

 Frequency — Cycles 



2500 



3C00 



Fig. 1 — Transmission Characteristic of Transcontinental Circuit — New York to 



San Francisco. 



distances, say from one point in a city to another point in the same 



city, non-loaded cable circuits equipped with distortion networks or 



attenuation equalizers for equalizing the attenuation, give good 



results. 



A good idea of the range of frequencies which can be transmitted 



8 Clark, Telephone Transmission Over Long Cable Circuits, Journil of A. I. E. E., 

 January, 1923. Also Bell System Technical Journal for January, 1923. 



