[RTTY] Question

[Phil Sussman]

I am trying to calculate the impedance of open wire transmission line and
I've stumbled across two different formulas.

I'm dealing with open wire feeder composed of #14 stranded wire with
ceramic insulators separating the line at 4 inches with each insulator
spaced at about one foot (between insulators).

One calculation gives a value of about 450 ohms and the other about 650
ohms. How am I goofing up? Any suggestions?

Thanks,

de Phil - N8PS