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:
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>
unshielded twisted pair ethernet cables:
> I think the nominal impedance is 150 ohms
?I think twisted pairs are closer to 100¦¸, I once measured one
and got 102¦¸.
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 92¦¸.
?If the spacing of the center to center distance is increased
0.003" the impedance becomes 100¦¸.
Or if the er is lowered to 1.9 the impedance is 100¦¸.
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 100¦¸.
????????????????????????????? Mikek
.
