IMPEDAXCK RRIDGES FOR MrXiACYCLF, UANT.F. 1011 



The (liroct-capacitanco measiiromeiits are useful iu the (lovelopmoui of 

 low \alue(l capacitors, aud the balanced-to-jiiround measurements are 

 helpful in evaluating low-admittance off-ground networks. 



CONCLUSION' 



Bridges have been developed for the measurement of impedance and 

 admittance parameters at megacycle frequencies with accuracies hei-eto- 

 fore i)ossible only at much lower fre(iuencies. Se\'eral of the twenty- 

 megacycle general-purpose biidges ha\e been built and are furnishing 

 useful measurements of net woiks and components. Experience with these 

 l)rid^(>s has indicated ranges for which supplementary si)ecial-purpose 

 bridges would l)e desirable, and two such bridges have been built: a 

 Maxwell ])ridge for low-valued inductors, and an admittance bridge for 

 low-\alued capacitors. One feature of all of these bridges not generally 

 available in commercial measuring instruments for megacycle freciuen- 

 cies is the provision of standards having a range of several decades. These 

 allow balances to be made with greater precision over a wider I'ange of 

 phase angles in the apparatus under test, and assure that the absolute 

 accuracy will not be limited by readability. This added precision is \'eiy 

 useful in comparing similar components or in measuring characteristics 

 such as temperature coefficient. 



ACKNOWLEDGMENTS 



The de\elopment of impedance bridges during the past thirty years 

 has been under the direction of J. G. Ferguson, and the work described 

 in this article has been under the supervision of S. J. Zammataro. Their 

 assistance in the preparation of this paper has been ^'ery helpful and is 

 hereby acknowledged. It is a pleasure also to acknowledge the contribu- 

 tions of a number of the author's colleagues particularly J. E. Xielsen 

 who was largeh^ responsible for the twenty-megacycle general-purpose 

 bridge, and L. E. Herborn for the fi\e megacycle Maxwell bridge. 



REFERENCES 



1. W. J. Shackelton, "A Shielded Bridge for Inductive Impedance .Measure- 



ments," Bell System Tech. ./., 6, pp. 142-171, Jan., 1927. 



2. W. J. Shackelton and J. G. Ferguson, "Electrical Measurement of Communi- 



cation .\pparatus," Bell System Tech. ./., 7, pp. 70-89, Jan., 1928. 



3. J. G. Ferguson, "Measurement of Inductance bv the Shielded Owen Bridge," 



Bell System Tech. ./., 6, pp. 375 386, July, 1927. 



4. S. J. Zammataro, "Im])edance Bridges," Bell Labs. Record, 8, p]i. 1(17 170, 



Dec, 1929. 



5. J. G. Ferguson, "Shielding in High-Freciuency Measurement," Bell Si/strm 



Tech. J., 8, pp. 560-575, Aug., 1929. 



