input impedance of an archimedean antenna

Hi, Have anybody worked with Archimedean single-arm (aka monofilar spiral antenna). The antenna is microtripe type. I have problem in feeding this antenna. As theory, we can feed it without using balun as done with the two-arm spiral type, Instead by using coaxal cable directly connect to the antenna. But we don't know the input impedance of the antenna (maybe greater than 100 ohm).
Does anyone know how many types of coaxial cable and their characteristic impedances.