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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



and a crystal with the necessary fixed and adjustable capacitors. The 

 small size is made possible partly by the high Q ferrite coil, and partly 

 by the circuit configuration employing it. As compared with filters em- 

 ploying air-core coils and having comparable cutoffs, the reduction in 

 size of these filters is very striking. 



The group receiving unit is shown with its plug-in filters on Fig. 31. 

 The filters are held in place by stud screws and nuts. The arrangement 

 shown on Fig. 31 is also used with different filters for the repeater ampli- 



10 20 30 40 50 60 70 80 90 1( 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 22 — Tj-pical line filter characteristics (Gl, 537A or 538A). 



