SHIELDING IN HIGH-FREQUENCY MEASUREMENTS 569 



The admittance between shields is considerable but due to the 

 method of construction the largest admittance is across the smallest 

 inductance and there is no intershield admittance added across the 

 highest decade. Accordingly, the effect is not as serious as might be 

 thought at first glance. 



In the case shown, the inductometer and the lowest decade are 

 generally used only in combination with the higher dials and under 

 these conditions they are not used at sufficiently high frequencies for 

 the admittance shunting them to have much effect. The greatest 

 effect of the admittance introduced by the shielding usually occurs 

 when the second highest dial is used at a high frequency with the 

 high dial set on zero. However, the admittance introduced across 



Three- Dial Shielded Adjustable Inductor. 



this decade is not appreciably larger than the distributed admittance 

 across the coils. The shielding, therefore, does not limit the range of 

 these inductance standards to any great extent. 



Adjustable Capacitor 



The units of an adjustable capacitor are practically always con- 

 nected in parallel and the problem of shielding them is that of shielding 

 a single capacitor. It is desirable to shield the decades from each 

 other if the capacitances are small as this facilitates calibration and is 

 easily effected. Where the capacitance is large, say over 10,000 /x/xf., 

 this precaution is unnecessary. The capacitance introduced from the 

 shield to the units has the effect of increasing slightly the value of 

 each dial setting. The form of construction of the shielding is similar 

 to that of the resistor shown in Fig. 5. 



