558 



BELL SYSTEM TECHNICAL JOURNAL 



directed to the receiving photographic emulsion through the aperture 

 of a single ribbon light valve. The latter, however, is operated by 

 the rectified picture currents instead of by the modulated picture 

 carrier current as used in the earlier equipment. This change results 

 in very simple yet efficient optical arrangements for receiving a 



Q 

 ZZ 



<^ 



ill 3 3.2 

 5 3.1 



80 



20 





500 1000 1600 2000 2500 3000 3500 4( 



FREQUENCY IN CYCLES PER SECOND 



Fig. 6 — Over-all characteristics of filters and delay equalizer. 



variable density constant line width picture with no apparent structure. 

 The aperture of the light valve, which is uniformly illuminated by the 

 incandescent lamp, is adjusted so that the width of its image on the 

 receiving emulsion is 0.01 inch. The height of the aperture, which 

 determines the exposure, is regulated by the instantaneous position of 

 the light valve ribbon and this is proportional to the received picture 



