IMPEDANCE BRIDGES FOR MEGACYCLE RANGE 



1001 



megacycle range. A ratio-arm bridge^ using external standards was 

 developed for precise measurements up to three megacycles. Intercon- 

 nection of bridge and standards using coaxial cords provided flexibility 

 of configuration resulting in an admittance bridge for high impedances 

 and a series-reactance bridge for medium impedances. These two bridge 

 circuits are shown schematically in (a) and (b) of Fig. 1. A separate, 

 self-contained Maxwell product-arm inductance bridge, shown sche- 

 matically in Fig. Ic and illustrated in Fig. 2, was designed primarily 

 for measuring low-impedance parameters up to one megacycle/sec. 

 Inductance was measured using calibrated air capacitors, and resistance 

 was measured by means of conductance decades employing wire-wound 

 resistors. The bridge included a double-shielded coupling transformer 

 and complete shielding not shown in the simplified schematic. 



To show clearly the scope and inter-relation of these three 

 bridge methods, it is helpful to plot their ranges on a Slonczewski 

 reactance/frequency chart ' shown in Fig. 3. In this chart, the top 

 frequency shown for the ratio-arm bridge is three megacycles, and for 

 the Maxwell bridge is one megacycle, as these are considered boundaries 



(a) ADMITTANCE BRIDGE 



(b) SERIES REACTANCE BRIDGE 



(c) MAXWELL INDUCTANCE BRIDGE 



Fig. 1 — Simplified schematics showing the basic circuits of three existing 

 bridges for use at frequencies up to about three megacycles. 



