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G6Tanuki · 6th Oct 2018, 5:36 pm

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.

6th Oct 2018, 5:36 pm	#11
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,996	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.