CARRIER SYSTEMS ON TELEPHONE LINES 



607 



freedom from voice interference with the receiving apparatus is 

 obtained, since this apparatus is designed to respond to very small 

 currents of this character but to discriminate sharply against other 

 currents. 



Tests and Adjustments of Apparatus. For the purpose of testing 

 and "patching" (i.e., interconnecting various equipment units in the 

 carrier system), jacks are provided as previously shown in Figure 19. 

 The equipment which is employed for testing and adjusting the 

 carrier apparatus provides means for measuring gains and losses at 

 the various frequencies encountered and includes a supply of testing 

 current at these frequencies. The general arrangement of the testing 

 apparatus provided for measuring gains and losses is shown in Figure 

 29. This is assembled with the other carrier equipment as previously 

 shown in Figure 20. It consists chiefly of means for switching a 

 known loss in the testing circuit, an attenuator, and a calibrated 

 thermocouple type measuring instrument for determining the value 

 of the current transmitted through this apparatus. The 1,000-cycle 

 current is used for practically all testing of the terminal apparatus. 



The testing equipment at a carrier repeater station is arranged in 

 a manner similar to that at the terminal stations, as previously shown 

 in a general way in Figure 29. It requires in addition, however, a 



TESnNCj* 



current'! 



TE5TINC CIRCUIT FOR MEASURING 1J033E5 



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TESTING 

 CURRENT!, 



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 -^^_ 



APPARATUS 

 TO BE 

 MEASURED 



"ei 



"ei 



TESTING CIRCUIT FOR MEASURING GAINS 



Figure 29 — Schematic of testing circuit for type "C" carrier telephone system 



carrier-frequency oscillator. Only high-frequency currents are trans- 

 mitted through the carrier repeater, hence the 1,000-cycle supply 

 employed at the terminals where modulation and demodulation of 

 these carrier currents occur, is not useful in testing the repeater 

 equipment. 



