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BELL SYSTEM TECHNICAL JOURNAL 



it increases the effective inductance and resistance variation with 

 respect to frequency. 



If this combination of impedances can be grounded at A we have a 

 complete system having no variable admittances. The principle may 

 be extended to include any number of series elements, the effect being 

 to place admittances across all of the elements but one, and to enclose 

 the whole system in one outer shield. Such a system for five elements 

 in series is shown in Fig. 1/. 



Parallel Impedances 



The shielding of parallel impedances is comparatively simple since 

 any number may be shielded individually and the shielding all con- 

 nected to the same point. In reducing the shielding of multiple 

 impedances to the simplest form the question arises whether it is 

 sufficient to include them in a single shield or whether in addition 



4 



Fig. 2 — Method of Shielding Parallel Impedances. 



they should be shielded from one another. If they are not shielded 

 from one another, there will be distributed admittances between them 

 which may cause errors. Preferably each should be shielded indi- 

 vidually. Fig. 2 shows such a shielding system for capacitors in 

 parallel. 



By following the procedure outlined above it is comparatively 

 simple to apply shielding to any combination of impedances in series 

 or in parallel in such a way that we will have all admittances to 

 external conductors from the shielded elements concentrated at 

 terminals or junction points of the system. 



Circuit Shielding 



In many cases it is impossible to connect the above combinations 

 in a given circuit so that the outer shield is grounded. In such cases 

 it is necessary to determine from the position of the network in the 

 system the effect of admittances from the shield to other shields and 

 to ground. To illustrate let us take the simple bridge circuit shown 



