LOAD RATING THEORY 643 



channels but for large numbers of channels the effects are readily 

 estimated from the change in the location of the asymptote shown on 

 Fig. 7. The equation of this asymptote is as follows: 



L = 10 logio iVr + (Fo + .115(72) + MPF -K Po - 3 db, 



where L = test tone load capacity, 



MPF = asymptotic multi-channel peak factor, 



Po = long average power of a reference volume talker in db 

 above .001 watt. 



The other quantities are as defined before. 



Peak Voltage Limiting 



The curves referred to in the preceding discussion have so far 

 neglected the effects of peak voltage limiting in the transmitters and in 

 the channel terminal equipment. Fundamentally, the effect of such 

 limiting is to modify the distribution of instantaneous voltages in the 

 individual channels. The extent of the modification, however, de- 

 pends on the volume. For single-channel systems it is obvious that 

 the improvement in load capacity due to limiting will be substantially 

 equal to the reduction in the maximum peak voltage. For a large 

 number of channels the improvement will approach the reduction in 

 the rms voltage per channel. An approximate method of accounting 

 for these complicated reactions is to consider that peak voltage limiting 

 modifies the upper end of the single-channel volume distribution. 

 Strictly the amount of such modification is a function of the number 

 of channels as well as of the characteristics of the limiters. Curve B 

 of Fig. 1 represents a compromise between the dififerent effects which 

 is believed to give reasonably accurate results for both small and large 

 numbers of channels for the limiting characteristic of present terminals. 



With the talker volume distribution modified in accordance with 

 curve B of Fig. 1, computations of the load capacity with voltage limit- 

 ing present may be made in a manner identical with that previously 

 described. Curve C of Fig. 7 shows the results obtained for this 

 amount of limiting. 



All of the load capacity curves of Fig. 7 are based on the equivalent 

 volume which would be exceeded 1 per cent of the time, irrespective 

 of the number of channels in the system. Where voltage limiting 

 is used, it appears reasonable to consider this percentage as fixed 

 because the action of the limiters serves to restrict the range of 

 voltages above the overload point, thus reducing the severity of any 

 overloading effects. When there is no limiting, and particularly 



