66 BELL SYSTEM TECHNICAL JOURNAL 



to zero. To take account of any constant delay it is sufficient to dis- 

 place the computed curve by an amount equal to the delay. The 

 characteristic of Fig. 1 may be separated into two components as 

 indicated in Fig. 2, where the top one gives rise to the in-phase com- 

 ponent and the bottom one to the quadrature component. Fc is the 

 carrier frequency for single sideband computations, and it is assumed 

 that Fc is great in comparison with the bandwidth. The characteristic 

 of Fig. 1 does not differ greatly from those used in the experimental 

 work. The quadrature component with the assumed characteristic 

 is somewhat more pronounced than with the experimental ones. 

 Figure 3 shows the equivalent low pass characteristics. Curve go 

 gives rise to the in-phase component and curve ho to the quadrature 

 component. Figure 4 shows the low-pass characteristic which is 

 equivalent to the original characteristic for double sideband compu- 

 tations with the carrier located in the middle. 



Figure 5 gives the computed envelope for a single transition when 

 this transducer is used on a single sideband basis. The figure shows 

 the rectangular sent wave, the envelope of the in-phase component, 

 the envelope of the quadrature component, and the envelope of the 

 resultant wave. Figure 6 shows the corresponding received wave for 

 the double sideband case. There is no quadrature component and 

 the in-phase component and the resultant are identical. Figures 7 

 and 8 show the single sideband envelopes for a unit dot and a unit 

 space, respectively. Figure 9 shows two dots in succession. Figure 10 

 shows the same case as Fig. 9 with the exception that dark current 

 14 db below the maximum current has been added. Figures 11 and 12 

 correspond to Figs. 9 and 10, the difference being that the dots are 

 shorter. Figure 13 shows a succession of five dots. Figure 14 shows 

 two dots as transmitted on a double sideband basis. In all the figures 

 but 11 and 12 the fundamental dotting frequency is 5 as indicated in 

 Figs. 1, 3 and 4. In Figs. 11 and 12 the dotting frequency is 45/3. 



In comparing these figures a number of things will be apparent. In 

 the first place, there is in the single sideband case a considerable 

 broadening of all the marks due to the presence of the quadrature 

 component. A second effect to be noted is that this broadening does 

 not cause the dots to run together nearly as much as might be expected. 

 This is particularly striking in Fig. 11 where the running together of 

 the two dots is only slightly greater than it would be with the in-phase 

 component alone. The reason for this is that when the dots tend to 

 run together the contributions from successive dots to the quadrature 

 component tend to cancel each other instead of adding to each other 

 as is the case with in-phase components. The broadening of Fig. 11 



