700 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



axis of the assembly is used for clamp- type connection. A guillotine clamp 

 for short-circuiting the input of the coaxial, as required in substitution type 

 measurements, is placed across the center wire and the projection parallel 

 to the axis of the assembly. The center conductor of each coaxial extends 

 0.500" beyond the tube, and is thus available for clamp type connections. 

 Soldered connections are thus completely eliminated in the use of the stand- 

 ards. 



Eccenlrkity 



Concentricity of the axes of wire and tube is assumed in most pubHshed 

 formulae which relate the dimensions of a coaxial structure to its electrical 



0.130 



0.125 



t 0.120 



-3 



5^0.110 



S^ 0.105 



<> 



•^"^ 0.100 



0.095 



0.090 



10 2 



BOTH STUD AND 

 HOUSING TIGHTENED 



40 50 60 70 80 90 100 

 CIRCULAR DEGREES FROM CLOSURE 



120 130 140 



Fig. 5 — Measured d-c resistance introduced by end 

 shorting device as a function of adjustment. 



constants. Consistent departures from concentricity, i.e. eccentricity, are 

 subject to analysis as regards effects on the electrical constants. In the case 

 of the standard coaxials, the use of straight, hard-drawn wire and tubing 

 combined with close-spaced support of the wire are all factors which reduce 

 eccentricity. However, it is obviously desirable to check the degree of resid- 

 ual eccentricity of the assembled coaxials point by point along each length. 

 A method developed to do this makes use of Biot and Savart's law.^ 



The external field, at any point P, of a long circular wire or tube carrying 

 a current I is given by 



r 

 * W. R. Smythe, Static and Dynamic Electricity, p. 272. 



(8) 



