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BELL SYSTEM TECHNICAL JOURNAL 



provided that there is no coupling between any of the four arms nor 

 any between them and the input and output circuits. This is in 

 practice a difficult result to realize, and this difficulty in obtaining a 

 simple but adequate system of shielding is one of the most serious 

 limitations to the bridge. 



Shielding 



Since the bridge contains no inductances of appreciable magnitude, 

 it is a comparatively simple matter to eliminate electromagnetic 

 coupling by using input and output transformers in toroidal form, 

 the input transformer being so designed that the core will not be 

 saturated when using the maximum input to the bridge. 



The elimination of the electrostatic coupling is not so simple, as 

 any electrostatic shielding introduced adds capacitance which, unless 

 due care is taken, will involve errors in the bridge. This means that 

 such capacitances must be limited to the corners BD and AC where 



GENERATOR 



Fig. 2 



