Re: Determining Zo for coax cable
I'd use a TDR and a terminated length of coax of known-impedance.
Join the unknown and known coaxes in series, then run a TDR. If you can see the transition then the two coaxes are of different impedance.
Though I've always got near-enough by measuring inner/outer diameter ratios. Oddities like RG62A/U [93 Ohm, used for IBM '3270' display-screens] are usually revealed by their construction before you bother to reach for any testgear.
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