64 BELL SYSTEM TECHNICAL JOURNAL 



transducers have been assumed such that the first two effects listed 

 above are absent. In the physical networks which are covered by 

 the experimental work and part of the theoretical work these effects, 

 while not absent, are found to be unimportant. The present discussion 

 therefore is principally concerned with the third of these effects, 

 namely, the quadrature component. 



In a recent paper Smith, Trevor and Carter ^ have studied, both 

 mathematically and experimentally, the matter of single sideband 

 transmission over a rather simple filter and have found that the enve- 

 lope is greatly distorted when the single sideband transmission is used. 

 They give characteristics of their filters and also the location of the 

 carrier frequencies so that it is possible to deduce that the first two 

 effects, listed above, are unimportant for some of the carrier frequencies 

 used. Their filter characteristics fall easily within the usual require- 

 ments for single sideband picture transmission at a speed appropriate 

 to the bandwidth. Substantially the sole source of distortion in their 

 work is the presence of the quadrature component, when the carrier 

 frequency is suitably located. 



Studies have also been made of a picture transmitting system of the 

 type described by Reynolds.^ This system makes use of single side- 

 band transmission which had been found in previous experiments to be 

 practicable. These previous experiments had shown that the quadra- 

 ture component was present and was of considerable magnitude, but 

 that the impairment in the picture was rather slight. They had also 

 shown that if sufficient current was transmitted for the darkest portion 

 of the picture the impairment could be reduced to the point where it 

 was practically not detectable, and that a fairly small dark current 

 would suffice. 



Computations 



The present section will be devoted to the computations of in-phase 

 and quadrature components corresponding to certain assumed idealized 

 characteristics, and reasons will be indicated why the picture impair- 

 ment should be materially less than might be expected from the ap- 

 pearance of oscillographic records of the signal. 



Figure 1 indicates the magnitude of the transfer admittance charac- 

 teristic which will be assumed. The characteristic is made up of two 

 half-cycles of a sine wave separated by a horizontal portion. The 

 phase shift vs. frequency characteristic is a straight line. In order to 

 simplify subsequent sketches this constant delay has been put equal 



•' R.C.A. Review, Vol. 3; p. 213, October 1938. 



* Bell System Technical Jourtial, Vol. 15; p. 549, October 1936. 



