TRANSMITTED FREQUENCY RANGE FOR CIRCUITS 



4SQ 



the ratio of approximately 3:4 in the number of channels obtained 

 within a griven frequenc\" range. However, this does not mean a 

 4:3 increase in the cost per circuit. The amount is considerably less 

 than this — depending somewhat on the type of s^^stem. In the pro- 

 posed coaxial system, which appears to be a favorable example, where 

 the attenuation increases roughly as the square root of the frequency, 

 a frequency band increased by one-third means that for repeaters of 

 a given t>pe and amplification the number of repeaters is multiplied 

 by approximately y^; that is to say, approximately 15 per cent more 

 repeaters are required. Furthermore, the line and terminal apparatus 

 costs are not changred in a case of this kind, and since they constitute 

 a major part of the total cost, the net increase in cost for the wider 



' 1000 2000 3000 ♦OOC 



FREQUENCY- CYCLES PER SECOND 



Fig. 2 — Representative transmission frequency characteristics of 3000-mile toll 



circuits. 



band width will be considerably less than 15 per cent — about five 

 per cent in the case of the longer systems where the terminal apparatus 

 costs are a small factor, and only a per cent or two in the case of the 

 ver>- short systems where the terminal apparatus costs predominate. 

 In the ideal case, using substantially perfect transmitters and re- 

 ceivers, articulation is improved as the upper limit in frequency 

 transmission is raised, as shown in Fig. 3. The increase in transmission 

 performance, which a step from 2750 to 3300 cycles, or 3600 c>-cles 

 for a single link, makes possible, is evidently still on the part of the 

 band width-articulation relationship where a measurable increase in 

 articulation may be expected. An improvement in band width accord- 

 ingly reduces the eflPort needed to interchange ideas, since fewer repe- 



