REFERENCE SYSTEM FOR TELEPHONE TRANSMISSION 555 



Comparison of Master Reference System and Standard 

 Cable Reference System 



Since the master reference system is to replace the standard cable 

 reference system for volume ratings, the two systems have been 

 compared by means of voice volume balances so that data obtained 

 in the future may be directly comparable in this respect with those 

 obtained in the past. The respective elements of the two systems, 

 as well as the systems as a whole have been compared. The station 

 set and cord circuit at the sending end of the standard cable system 

 are taken as comprising the transmitting element of that system and, 

 likewise, the corresponding apparatus at the listening end as the 

 receiving element. In these measurements the reflection gain at the 

 junction of the standard cable line and the output terminals of the 

 transmitting element of the standard cable reference system has been 

 taken as part of the transmitting efficiency of that element. Similarly, 

 the reflection gain at the junction of the standard cable line and the 

 input terminals of the receiving element of the standard cable reference 

 system has been taken as part of the receiving efficiency of this 

 element. 



In the voice calibration of the master reference system to determine 

 the adjustments which make this system equivalent on a volume 

 basis to the standard cable reference system, eight series of voice 

 tests were made. The purpose of the first five series of these tests 

 was to determine the adjustments which make the master reference 

 system with transmitter distortion network No. 1 and receiver dis- 

 tortion network No. 1 inserted in their respective elements, equivalent 

 on a volume basis to the standard cable reference system. The 

 purpose of the sixth and seventh series of tests was to determine the 

 volume effects of the insertion of these distortion networks in the 

 reference transmitter and receiver. The eighth series of tests was a 

 direct comparison of the master system without distortion networks 

 and the standard cable system, and so serves as an overall check on 

 the determinations of the preceding tests. 



In the first series of tests a comparison was made of the reference 

 receiver with its distortion network and the receiving element of the 

 standard cable system by interchanging the two in the standard cable 

 system, with 24 miles of artificial cable in the line. The receiving 

 element of the master system was adjusted so that its sound output 

 was judged to be equal for this condition to that of the receiving 

 element of the standard cable system. In the second series of tests 

 a similar comparison was made of the reference transmitter with its 

 distortion network and the transmitting element of the standard 



