Re: slightly off topic feel free to delete
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To add to this¡ ? The number of twists per foot determines the differential-mode susceptibility of the cable. More twists per foot, higher rejection of differential energy. ? It does not improve the Common Mode environment susceptibility though ¨C the cable is still a monopole receive or transmit antenna. ? Shielding and properly terminating the shields helps with Common-mode susceptibility and emissions. ? Ross ?
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From: [email protected] < [email protected]> On Behalf Of Tom Lee Sent: Wednesday, March 29, 2023 10:16 AM To: [email protected]Subject: Re: [Test Equipment Design & Construction] slightly off topic feel free to delete ? And I should have added that the impedance is measured at a frequency of 100MHz.
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 3/29/2023 09:14, Tom Lee wrote: 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 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
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