BALANCED RADIO FREQUENCY CABLES

Abstract : The results of this investigation of twin and dual coaxial cables show that the chief causes of transmission unbalance are: (1) Eccentricity of the twisted pair within the core and shield braid in twin cables, (2) Uneven twisting of the conductors in twin cables and of coaxial cables in dual cables, (3) Variation in the length of conductors or separate coaxial cables. Two equations have been derived. One correlates transmission unbalance to the measured capacitance unbalance. The second equation relates transmission unbalance to conductor length differences or capacitance unbalance. As a result of the production of the improved RG-22A/U and the new dual coaxial cables, it was found that values of transmission unbalance of 3% at 100 megacycles can be attained. It is apparent that the target value of 2-1/2% transmission unbalance for RG-22A/U has been very nearly achieved. However, in view of the findings of this development, it is felt that the 1% value at 100 megacycles specified for the dual coaxial cable was set too low initially. It is felt that with measuring and manufacturing techniques at their present level, dual coaxial cables can be fabricated with transmission unbalance values as low as 3% up to frequencies of 100 megacycles. (Author)