75 ohm coax instead of rca cables

My approach to such questions i nots based upon general understanding of electricity and electronics and not pon specific configurations.

When you say "line out" I presume you mean an audio line. You are not specific as to what is driving the line and what (the load) is being driven. The length of the run can also be important.

If all you need is conductors, RG-6 will do just fine. On the other hand, if you are taking output from a pre-amplifier at relatively high impedance, a long run of cable of that kind could kill your high audio frequencies if not terminated properly. I do not remember just what the capacitance of RG-6 is, but 15pF per foot is not far off. The resultant

2.25nF could, but might not, lead to considerable frequency distortion.

Please tell us just what you are doing in greater detail.

Bill

A brief search shows that alt least one make of RG-6 is 16.2 pF / foot.

Most likely all will be well will be well unless you encounter ground loop issues. In that event transformer isolation will most likely cure it.

In which case you might as well run a balanced line with a bit of cheap twisted pair instead of expensive co-ax.>

My impression was that the OP had plenty of RG-6 cable on hand. A quick calculation indicates that the cable as a capacitor will still give a bandwidth of tens of kilohertz with a source impedance of 600 ohms. Good enough. It still would be good to know the source and load impedances.

Bill.

Yes it's an audio signal, the best I can describe it is the signal is the same as a "tape out" signal on a stereo receiver and I'm going in to the "tape in" input on the second stereo amplifier. I have a stereo in one end of my building and I'd like to carry the audio to the other end. I have several hundred feet of RG-6 duplex coax and want to use that instead of buying multi-conductor cable. I want to feed the signal to a secondary amp so I can control the volume, balance, tone etc. without going to the other end of the building which I would have to do if I simply added remote speakers.

I do not know what you mean by "duplex coax." Do you mean a pair of RG-6 cables attached to each other?

In any event, just try it. It certainly is not likely to be worse than the multi-conductor cable you do not have now. If you have problems, just add a resistor network that makes each cable look like it is terminated in 75 ohms. This includes the input impedance of your remote amplifier.

Bill

It should be easy enough to just run the cable down hallways and through doors, for a temporay test. A couple hundred feet of Rg6 should be no problem for a lo Z output preamp. I would expect the output z to be 1000 ohms or less and the input z to be

10k or more. The cable is to short to act like a transmission line at audio frequencies, so terminating the cable has no benifit. If anything, noise pickup might be an issue, so be carefull to keep the cable clear of motors, dimmers, AC wiring etc. Ground loops (hum) might also be an issue especially seeing as the amplifiers are likely to be on different power circuits. There are thingys called isolation transformers that can solve that issue and you can still use the Rg6. Going balanced would require that the inputs and outputs of the amps be converted to balanced, and transformers can do that to, but RG6 is not meant for balanced signals. Twisted pair like a phone line is meant for balanced signals. There are F to RCA adaptors that might make your connections easier.

Yep duplex coax is a pair of shielded conductors in a common jacket. I'll give it a try, at the least if I have problems I've got a pull wire in the plenum for twisted pair conductors... thanks to everyone that chimed in. I'll post again how everything works when I get the project completed

Finished installing the coax and everything is working fine. I haven't completed the ac wiring in the same plenum so I may encounter an induced noise issue. I'll probably add an isolation x-frmr to be safe.

It might be a good idea to ground the shield at only one end. This is a practice from the 50's with phono millivolt pickups. where a ground loop through the shield can cause problems. Try this before consideration of an isolation transformer,.

In many juristictions it is not permitted to run "Signal" cables in the same duct as Mains Power cables. But the risk is yours.

John G.

I'm aware of the NEC, but in this case I'll take the risk, besides that I don't live in any area that is governed by electrical building codes.

Idiot. ONE of the reasons you do not do it is because you can inject noise into your communications lines.

It is pretty stupid when the solution is merely to place another layer of steel between them.

An isolation transformer will not be a solution for the noise. Duh!

"life imitates life" wrote in message news: snipped-for-privacy@4ax.com...

take it easy tiger we're only talking about some wire and a little noise, it's not like I'm unleashing the mother of all electrical faux pa's

Well, "some" RG-6 uses copper plated steel for the center conductor. At VHF/UHF frequencies this works almost as well as pure Cu.

But at audio frequencies, it could make a difference.

For a long run at audio frequencies, I would think you are better off with some kind of balanced transmission line with shielding. Sometimes it doesn't pay to be too cheap. Save your RG-6 for when you want to install another TV.

To my 60 year hearing I can't detect anything abnormal. The center conductor is copper, I've never scrapped it to see if it solid on plated however it bends like cu. I've got plenty of RG-6 left probably around another 700', the satellite guys left this at my house after they finished installing the dish. Guess they didn't want to pick it up and throw it in their truck.