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BELL SYSTEM TECHNICAL JOURNAL 



also shows the new equipment provided at San Francisco on the two 

 program circuits under discussion. The three right-hand bays accom- 

 modated the special equipment. 



In making transmission measurements, the circuit under test was 

 first split up in a number of sections and each section was then meas- 

 ured at four test frequencies, namely, 50, 100, 1,000 and 7,000 cycles. 

 If the results were not within required limits the attenuators and 

 equalizers were readjusted as required. The various sections were 

 then connected together and the overall circuit measured at several 

 frequencies. Figure 22 shows the transmission-frequency character- 



'~ 30 50 100 500 1000 5000 10,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 22 — Transmission frequency characteristics of circuit No. 1, Chicago to San 



Francisco. 



istics of circuit 1. The solid line is the average of nine measurements 

 while the dashed lines show the extreme deviations obtained for any 

 of the nine measurements. Figure 23 shows corresponding data for 



01 -6 



2 2 



t- 30 50 100 500 1000 5000 10,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 23 — Transmission frequency characteristics of circuit No. 2, San Francisco to 



Chicago. 



circuit 2. For comparison purposes the average characteristics of the 

 two circuits separately and the two of them connected in tandem 

 making a loop circuit of over 5,000 miles are shown on Fig. 24. 



Other measurements were made to determine whether non-linear 

 effects were produced. For example, two frequencies were applied 



