XLEagle wrote:
> This is not a LabVIEW, but a basic electrical question. I think many LabVIEW guys have an EEE background. Please forgive me for my ignorance if the question sounds too simple to you.
>
> Impedance values (either 50 Ohm or 75 Ohm) are specified for BNC connectors/cables. What does this impedance value mean? I know the resistance value of a BNC cable is effectively 0 Ohm. My guess is that the value must be the impedance at a particular frequency, but I am not sure. Can someone clarify? Also, does this impedance value matter in data acquisition?
>
> Thanks.
>
> XLE
The impedance of a cable is the impedance seen looking into the near
end, when the far end is terminated in that impedance. So if the cable
is 50 Ohms, and you terminate the far end in 50 Ohms, then the near end
will look like 50 Ohms.
If you take a 50 Ohm cable, and terminate the far end in 75 Ohms, then
the impedance seen looking into the near end will depend quite a lot on
frequency. But as long as you terminate the 50 Ohm cable in 50 Ohms, the
frequency you measure will be close to 50 Ohms, irrespective of frequency.
Read up on transmission lines, if you want to know more.
--
Dave K
http://www.southminster-branch-line.org.uk/
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