202 BELL S YSTEM TECH NIC A L JOURNA L 



stators were tied into the same source of power, no separate synchronizing 

 means was necessary. 



Figure 7 is a photograph of the cathode ray trace of the output of the 

 transmitter tube when signals were being sent over three channels. A 

 circular sweep circuit w^as used which distorted the signals somewhat. The 

 shape of the pulses is shown better in Fig. 8 for which a linear sweep was 

 employed. Signals were put on three channels, two of which were adja- 

 cent. The double-humped top of the pulse is caused by the window in the 

 screen being slightly narrower than the beam width so that as the beam 

 crosses the window, the greater densities in the edges relative to the center 

 give this shape. A flat-topped pulse may be obtained by making the win- 

 dows wider than the beam. 



In conclusion the writer wishes to acknowledge his indebtedness to a 

 number of his colleagues in the Laboratories for aid in the development of 

 the tube. The 30-channel multiplex system was set up with the aid of 

 Mr. W. H. T. Holden. 



