1004 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



frequency of twenty megacj^les was decided upon as a design objective 

 with a basic accuracy of ±0.5 per cent for the major component. The 

 immediate need was for a general-purpose bridge, but it was expected 

 that special-purpose bridges having better accuracy would be required 

 later. 



GENERAL PURPOSE 20-MEGACYCLE BRIDGE 



It was decided first to develop a single bridge unit which would em- 

 brace both admittance and series impedance methods, and thereby cover 

 a reactance range from a few ohms up to nearly a megohm, as sho^^^l in 

 Fig. 4. Such a bridge would combine the features of (a) and (b) of Fig. 1. 

 There were numerous departures from the earlier designs, however, in- 

 cluding the use of a series range capacitor to reduce the size of the series 

 capacitance standard, the use of deposited carbon resistors, the form 

 and construction of both conductance and resistance standards, and 

 especially the use of transformer-coupled inductive ratio arms. 



O 10^ 



['admittance ^ 



k<> METHOD CsJ 



.^^ 



0.1 0.5 1 10 20 100 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 4 — Reactance/frequency chart applj'ing to the general-purpose bridge 

 shown in Fig. 5. 



