Re: post 3.
For the measurements, I customarily use an HP 4332A LCR meter. It uses two freqs., depending on the range selected (L or C). Highest is 100 kHz; lowest is 1 kHz.
For capacitance, I can also use an R & S capacitance meter (KARU 510). Highest freq. is 175 kHz; lowest is 5 kHz.
Of those two instruments, the shortest wavelength is 1700 m. (≈ 175 kHz).
Any cables that I will ever be likely to measure the Zo of will a lot shorter that 1700 m. !
Al.