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Can any RCA cable be used as a digital coax or does it have to be a 75ohm one?

post #1 of 13
Thread Starter 

So basically my television has a Digital Audio In jack, and my receiver box has a Digital Audio Out jack.

I have a bunch of unused "regular" RCA cables lying around. These RCA cables are intended to be used as analog interconnects.

If I wish to exploit this digital audio function, would these regular RCA cables work, or do I need a special 75ohm digital coax cable (actually not expensive)?

 

Thank you very much.

post #2 of 13

Theoretically or in practice?

 

Theoretically there is nothing about any given RCA cable (no matter how its made) that is acceptable for a 75ohm connection. 

 

In practice, do whatever you want unless the wire run is more than about 10feet. Honeybadger dont care and neither does your digital signal. 


Edited by nikongod - 7/18/11 at 7:53pm
post #3 of 13
Thread Starter 

...OK, so what you are saying is that there is no difference between a "regular" RCA cable and a special "digital coax" one?

post #4 of 13

A digital cable uses 75 Ohm cable. It should have 75 Ohm plugs and sockets, but laziness on the part of manufacturers means that it doesn't. I wouldn't worry about it for your TV though.

post #5 of 13

A digital cable is 75 ohm based on how thick the dielectric (plastic) is between the center conductor and the shield.  You can set the cable to whatever impedance you want if you're a cable factory based on that thickness.  The RCA plugs themselves in a few limited cases (like the Canare RCAP) can be 75 ohm too, with a specific design and termination technique/tools to keep the shield and center conductor properly spaced.  For a digital cable to be within spec it has to be 75 ohm.  However, it's questionable how many problems you'll hear with a non-spec cable (say, you take an audio RCA cable, and plug it in) unless you really know your gear and recordings.  

post #6 of 13
Quote:
Originally Posted by scootermafia View Post

A digital cable is 75 ohm based on how thick the dielectric (plastic) is between the center conductor and the shield.  You can set the cable to whatever impedance you want if you're a cable factory based on that thickness.  The RCA plugs themselves in a few limited cases (like the Canare RCAP) can be 75 ohm too, with a specific design and termination technique/tools to keep the shield and center conductor properly spaced.  For a digital cable to be within spec it has to be 75 ohm.  However, it's questionable how many problems you'll hear with a non-spec cable (say, you take an audio RCA cable, and plug it in) unless you really know your gear and recordings.  


+1
post #7 of 13
Thread Starter 

Well that's something.

So I'll interpret vague answer as yes?

post #8 of 13
The answer is YMMV. Theoretically, you need a 75ohm cable, while realistically, any cable will work. I will have no qualms about doing the latter unless someone with a scope or equipment can tell me there is a difference that can be heard audibly.
post #9 of 13
Thread Starter 

Well I jacked-in a regular RCA cable as a coax.

"Maybe" the sound is "cleaner". I don't know.

post #10 of 13

^ banned at his own request.. thats a new one..  ;-)

post #11 of 13

The rated cable impedance is most significant when the termination loads match. For example,  TVs and electronic boxes for cable TV are typically 75ohms and you can buy 75ohm coaxial cable for interconnects.  An impedance mismatch would result in signal reflections and loss of efficiency. A coaxial cable is a transmission line for TV signals.

 

But a coaxial cable for audio frequencies is no longer a transmission line. I think it is mainly a capacitive load.

post #12 of 13

I have been trying to get my soundbar for my TV to work on the digital link from my FIOS set top box. It works with the analog link but I am using that to send audio to my outside porch. If I use a analog cable on the digital link,  should I get sound but mabe just not good sound? I get nothing. Also tried a optical cable from the set top box to the Sound bar, nothing. The Verzion help line said all 3 audio outputs on the settop box could be used at the same time. I spent a hour with the help people at PHILLIPS (soundbar) who I think gave up and somehow disconnected from me. 

Thanks Phil

post #13 of 13

Most after-market RCA cables have a 75 Ohm Radio Frequency Characteristic Impedance almost by accident.  From a manufacturing point of view, it's the sweet spot in material & manufacturing costs.

 

Digital audio & digital video operate in a very different frequency band than does TV channel signals.

 

Digital audio SPDIF is a very robust system.  The cable Characteristic Impedance is only important in very long cables.

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