If you take random hookup wire and twist it with some random pitch, you'll often see something closer to 100 than to 150, but 150 is certainly not out of the question. That said, CAT5 is spec'd at 100 ohms, plus or minus 5 ohms.

-- Cheers
Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070

On 3/29/2023 08:51, Mikek wrote:

> unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms

?I think twisted pairs are closer to 100Ω, I once measured one and got 102Ω.
It is dependent in the diameter of the wire and the thickness of the insulation.
Using the calculator,?
I get a slight lower number for a Cat5 wire I have, it is 24 gauge with polyethylene?
insulation that is 0.075" thick. This puts the 0.0201" wire spaced 0.015" by the
insulation that has an er of 2.25 at a center to center distance of 0.035" and an impedance of 92Ω.
?If the spacing of the center to center distance is increased 0.003" the impedance becomes 100Ω.
Or if the er is lowered to 1.9 the impedance is 100Ω. i.e. I could have a little error in the thickness
and/or the er of the insulation, a small change could get me close to 100Ω.

????????????????????????????? Mikek

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