THE L3 SYSTEM — DESIGN 



789 



of the repeater as functions of frequency and the overload performance 

 of the repeaters. These factors depend on the repeater spacing and cable 

 loss characteristic, electron tube parameters, achievable feedback, and 

 the bandwidth to be transmitted. Thus, in the design procedures the 

 dependence of these properties on repeater gain and bandwidth are 

 determined and used in adjusting the system parameters for a final 

 compatible design. Figs. 5 and 6 show the noise and linearity properties 

 of the final L3 repeater. The four mile repeater spacing requires a re- 

 peater gain shown on Fig. 7. 



■90 



5-100 



•110 



-120 



0.2 Q.3 0.4 0.6 0.8 1.0 2 3 4 5 6 8 10 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 5 — L3 Auxiliary repeater noise characteristic. 

 2.15 SIGNAL MECHANISMS 



A signal-to-noise plan which contemplates transmitting the complex 

 wave form of the combined telephone and television channels through 

 1,000 auxiliary amplifiers and about 200 flat amplifiers with performance 

 factors that are variable with frequency will depend very strongly on 

 the detailed analysis of the interactions between the signals and the 

 repeater system characteristics. In developing this aspect of the signal- 

 to-noise design four related phenomena had to be examined in detail. 



2.151 Intermodulation Between Signals in Different Parts of the Band 



In the classical multichannel modulation theory for a large number 

 of message channels, the modulation noise generated by interaction of 

 the speech signals due to the non linear characteristics of the amplifier 

 is shown to be equivalent in interfering effect to random noise. In ad- 

 dition to this type of interference in message channels, cross modulation 

 between components of the message and television signals result in a 

 host of specific individual modulation products which have been ex- 

 amined by determining their amplitude, duration and probability of 



