MULTICHANNEL MODULATION SYSTEM 39 



V. Performance 



In general the behavior of the system has shown promise for toll plant 

 application. Among other things the stability realized in the adjustments 

 of the coder and decoder, and the apparent absence of aging or other drift 

 in the compressor and expandor have been gratifying. A daily check of the 

 focus and centering in the coders and of the time constants in the decoders 

 appears adequate to keep them in optimum adjustment. The synchronizing 



Fig. 24. Output of decoder (vertical) vs. input to coder (horizontal). 



gear has been found equally easy to maintain. On the other side of the 

 ledger, occasional breakdowns have pointed up the need for alarm and auto- 

 matic replacement facilities in any version of the system which might be 

 developed for commercial service. 



A few measured characteristics are given in this section in addition to the 

 compression and audio gain-frequency characteristics already shown (Figs. 

 14 and 11, respectively). 



Input-Output Characteristics. The diagonal trace in the oscilloscope 

 pattern of Fig. 24 shows the relationship between the input of a coder (hori- 

 zontal deflection) and the output of the corresponding decoder (vertical). 

 For this pattern a full-load audio signal was applied to the input of the odd 



