hi all,
can anybody plz tell how do we measure cahracteristic impedence of a cable, may it be coaxial, stp, utp or power cable.it looks impedence matching and trying to get the maximum power. i s there any other way?
characteristics impedence
Nov 24, 2007
5 Replies
If you really want to do this look here: http://72.14.205.104/search?q=cache:-K9ty8myB2YJ:sist.fnal.gov/archive/2000-topics/Owusu/owusu.doc+measuring+characteristic+impedance+of+cable&hl=en&ct=clnk&cd=8&gl=us
Tom
Well, you can safely forget about the concept for an equipment power cable.
Graham
Just measure it.
1] Measure the "L" with the lead ends short circuited. 2] Measure the open circuit "C" 3] Then Zo= square root of L/CSome I did last year ...
2mtr of "75ohm" coax L=1.48uH C=146pF ... Zo=100ohm* 2mtr of 50ohm coax L=0.83uH C=168pF ... Zo=70ohm 2mtr of 'twin flex' L=1.23uH C=70pF ... Zo=132ohm 2mtr of 'mains cable' L=2.84uH C=281pF ... Zo=100ohm 3mtr CAT5 patch cable L=2.51uH C=157pF ... Zo=126ohm(measured twice, still same result!)
"john jardine"
** Likely the frequency you used for the L and C measurement was not in the normal RF range.Zo for co-ax tends to rise at low RF and audio frequencies.
....... Phil
I would either look it up in the cable spec, calculate it, or measure it with a TDR.
Good Luck! Rich
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