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BELL SYSTEM TECHNICAL JOURNAL 



such as brass or aluminum which will give mechanical stability without 

 excessive weight.^ 



INPUT 

 JACK 



■EGRATING 1/ , 



NDENSER "ir^]_ 



Fig. 8 — Schematic of a 3 hnc echo box. 



-IN23 CRYSTAL 



OUTPUT METER 

 (WICROAMMETER) 



BACK CAVITY-_ 

 BEARING 



*^OTION 



INPUT 

 JACK 



Fig. 9 — Schematic of a 9 kmc echo box. 



The movable plate is driven by the piston which operates in a close-fitting 

 bearing. The drive mechanism translates the rotary motion of the tuning 



