72 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



Table IV — Specific Operating Channels Having No Third Order 

 Intermodulation Interference 

 p is the number of interference free operating channels which can be obtamed 

 from n consecutive channels. 



* Neither 3rd nor 5th order interference exists with this selection of eight op- 

 erating channels. 



possible number from which p channels having no 3rd order interference 

 can be selected. 



A plot of p versus n based on the above table is shown in Fig. 3. 

 The curve which includes both 3rd and 5th order intermodulation prod- 

 ucts shows that 300 consecutive channels must be made available to 

 provide for the careful selection of 10 operating channels which are in- 

 terference-free at all times, regardless of the traffic load. For comparison, 

 it was shown earlier (Fig. 2) that more than 500 consecutive channels 

 must be available to permit picking at random 10 operating channels 



UJ u 



■^ ui 



UJ UJ 



UI >■ 

 HO, 



- 10 



u 



3 

 Z 



II 



200 



400 



2 3 4 5 6 8 10 20 30 40 60 80 100 



n = NUMBER OF CONSECUTIVE CHANNELS 



Fig. 3 — Number of consecutive channels n required to provide a number of 

 interference free operating channels p. 



