8 BELL SYSTEM TECHNICAL JOURNAL 



The new apparatus shown in Figs. 4 and 5 not only costs but one- 

 tenth as much and weighs one-quarter as much as the older apparatus 

 but also has electrical advantages which enable a new and improved 

 measuring technique to be employed. The generator is a magneto 

 inductor alternator driven by a 50-cycle or 60-cycle induction motor 

 and gives a constant output without attention. The output is ad- 

 justed at the factory or on installation. Some of these machines have 



Fig. 5 — One thousand-cycle magneto generator used generally for transmission 

 testing. Cover plate removed to show the generator construction. Overall length 

 7 inches. 



been running continuously for about a year without showing any 

 appreciable change in output. They can, therefore, be mounted 

 permanently in an office and the output terminals wired to convenient 

 testing points so that the generator need not be carried around. 

 Because of this output stability, it is not only unnecessary to have an 

 experienced tester at the distant end of the circuit but in the larger 

 offices auxiliary switching equipment is arranged so that testing power 

 can be supplied automatically to one end of the circuit by direction of 

 the tester at the other end, who simply calls or dials a designated 



