where is the 75ohm part of digital rca's?

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where is the 75ohm part of digital rca's?

Postby mildew » 24 Nov 2016, 23:51

i just purchased a '75ohm digital" cable for an a/d converter.

If i measure the resistance from tip to tip its close to 0 ohms, from ground to ground its close to 0 ohms, from ground to tip its open circuit.

the cable is clearly marked "75 ohm digital" - can anybody explain to me what that actually means?

**edit i think i get it now, its the impedance not the resistance thats 75 ohm, info here ..

http://forums.audioholics.com/forums/th ... mean.1980/
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Re: where is the 75ohm part of digital rca's?

Postby deltafred » 25 Nov 2016, 10:28

It is unfortunate that resistance and impedance are both measured in ohms. It causes no end of confusion unless you understand a little about electronics (and for cables a bit of transmission line theory also helps).

Much like speakers, if you put a multimeter across an 8 ohm speaker it reads a resistance of around 5 to 6 ohms. What you are seeing is the DC part, the inductance accounts for the remainder once you put AC across it.

(A speaker may have a nominal impedance of 8 ohms but if you look at an impedance plot across the frequency range it is rarely 8 ohms.))
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