The measured effects at super-high frequencies of irregularities in coaxial cables

If the local characteristic impedance of a cable is not uniform along its length its characteristic impedance at high radio frequencies will be frequency sensitive because of internal resonances. The results of the ¿uniformity of impedance` test of the British Services Specification DEF-14A carried out on about 50 cables are discussed. It is shown that there is a correlation between the measured impedance variations and in the first place the measured variations in cable core diameter and also with the amount of air trapped within the dielectric during the extrusion process.