COAXIAL IMPEDANCE STANDARDS 



699 



(c) The center wire is drilled and tapped to a depth of xV at one end to 

 accept the 0-80 screw carried by the stud. After the disc is tightly 

 pressed against the tube as in (a), the center wire screw stud is turned 

 until the center of the disc is drawn tightly against the end of the 

 center conductor. The stud projects from the end of the housing and 

 is milled at its end to accept a torque wrench. The wrench provides 

 the means for development of repeatable pressure of the end of the 

 wire against the center of the disc. 

 Experimental data on the relative pressure versus d-c. resistance char- 

 acteristics are illustrated by the curves of Fig. 5. Disc pressure on the cen- 

 ter wire is controlling as would be expected. The total d-c. resistance in- 



RUBBER ' 

 PRESSURE GROMMET 



0-80 SCREW 

 (TO ENGAGE CENTER WIRE) 



-HOUSING 



Fig. 4 — Assembly detail, end-shorting device. 



troduced by the short circuit is of the order of 0.1 milliohm, which includes 

 the contact resistance. On the basis of experimental observation the resist- 

 ance at radio frequencies appears to be more stable because the area of 

 contact becomes of less importance as frequency is increased. The inductance 

 introduced by the disc is negligible for all lengths and frequencies. The a-c. 

 resistance of the disc is equal to its d-c. resistance up to about 1 mc where 

 complete wave penetration ceases and skin effect becomes apparent. Above 

 2 mc the disc resistance increases as the square root of frequency. 



Connection — Test End 



A connector currently in use at the test end of the outer conductor is 

 shown in position in the photograph, Fig. 3. The projection normal to the 



