[Pepsione1]

This isn't audio related btw but I could certainly use some help.

I am trying to make DIY communication cable. The manual specifies that you need a cable with 100ohms nominal impedance. The one I have I tested to be 3ohms only. I just tested from one end of the wire to the other with the multimeter and no load.

Did I do it correctly? Is less resistance better? Mean what I have on hand is more than sufficient for what is specified.

 

[jar]

Resistance and impedance are not the same thing, even though they're measured in the same units. Resistance is the opposition to DC current flow. Impedance is the opposition to AC current flow. Characteristic impedance of a transmission line is related to the DC resistance, the inductance, the conductance of the dialectric, the capacitance, and frequency. You can measure impedance with a network analyzer (an expensive piece of test gear).

Edited to add: A very fuzzy idea of transmission lines is about where my electrical engineering knowledge stops. I'm a digital guy. I'm sure amb or tangent can give you a much more useful explanation.

 

[fortney]

Check Mouser, or other companies that sell cable such as AES or maybe directly from Belden--for cable, coaxial cable, etc and maybe they have something you want. I know they have 50 and 75 ohm.

F

 

[tangent]

100 ohm cable is uncommon.

I would first search briefly at the major distributors; I'd add Markertek to the ones already mentioned. I wouldn't spend much time looking there because it's quite possible that the popular distributors won't carry something odd like this. You might have to go to a specialist supplier. In that case, the best course would be to search cable manufacturers' web sites to find product numbers, then Google for distributors of that cable.

 

[MisterX]

Does anybody here want to guess what the characteristic impedance of Cat 5 cable is?

 

[n_maher]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif Does anybody here want to guess what the characteristic impedance of Cat 5 cable is?

Oooh! OOOH! I know! 100 ohm!

 

[jcx]

yes the range for twisted pair AC impedance overlaps 100 Ohms depending on wire diameter, insulation dielectric&thickness and turns/inch

a fast 'scope and function generator with experimental series drive and teminating resistors can get you pretty close if you know what to look for