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amer7909
Active Contributor

Join Date: Aug 2008
Posts: 16

how to measure UTP cable resistance

11/27/2008 12:09 PM

Dears

I would like to ask about how to measure UTP cable 100 ohm resistance,and on what it depends ?
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Anonymous Poster
#1

Re: how to measure UTP cable resistance

11/27/2008 11:14 PM

Attach a pulse generator and a CRO to one end of the cable in parallel, then attach adjustable resistance to the other end. You will see a reflection from the cable - the edges of the pulse will not look clean, but will instead have a lot of steps. Change the resistance until there is only a single step visible at each edge, this is equal to the cable impedance. Note, to do this you would need a fair length of cable (for an average sort of pulse generator and CRO the rise time might be 10ns and you will need at least 5m to see things clearly).

Cable characteristic impedance depends on a lot of things including the insulation material, conductor diameter and spacing, proximity of other conductors, etc. Complicated subject. Link anyone?
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Haajee
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Join Date: Feb 2006
Posts: 1758
Good Answers: 6
#3
In reply to #1

Re: how to measure UTP cable resistance

11/28/2008 9:00 PM

Regards.

A good answer.

But I take the oppertunity to add that cables are manufactured according to specs.

All the specs are given in the cables nomenclature.

Contact the supplier.

For unknown cables charteristics there Equipment called normally TDR Test Equipment.

It is for the fault finding on running cables but can be used in labs for cable testing

Time-Domain-Reflectrometrery

I add one mark to your answer

Regards
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Haajee
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Join Date: Feb 2006
Posts: 1758
Good Answers: 6
#2

Re: how to measure UTP cable resistance

11/28/2008 8:50 PM

Regards.

Do you mean ZO = Characteristic Impedance ?
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