SCIN

[rickcr42]

"Shield Current Induced Noise"

another great read from the Rane Notes library

[rowuk]

where is the link?

[rickcr42]

Jun 23, 2008 20:03:27 GMT rowuk said:

where is the link?

it would help a bit i guess ;D

www.rane.com/note166.html


more content :

www.audiosystemsgroup.com/Shield_Current_Induced_Noise.pdf

www.audiosystemsgroup.com/SCIN-2.pdf

[dotnet]

Interesting. I seem to remember an audio builder's mantra from when I was an apprentice: never use the shield as a conductor, and only connect one end to the ground (the last bit obviously to avoid ground loops). I don't recall who taught me that but I stuck to it and always used shielded twisted cable for audio interconnects (internal or between devices), with the shield connected to ground at the source.

One thing I've always wondered about and didn't get around to try out for myself is how well a shielded Cat-6 cable would perform as TV antenna cable. On paper, the loss would be huge, due to the rather high capacitance of the cable. Then again, Cat-6 is used for Ethernet cable runs of 100m and more, at frequencies of several hundred MHz. Then again, a decent coax cable like RG6 has virtually no loss up to 1GHz over distances you'd encounter around the house. Impedance matching may also be a problem with Cat-6, I don't think it has a very predictable impedance.

Cheers
Steffen.

[rickcr42]

One thing I've always wondered about and didn't get around to try out for myself is how well a shielded Cat-6 cable would perform as TV antenna cable. On paper, the loss would be huge, due to the rather high capacitance of the cable. Then again, Cat-6 is used for Ethernet cable runs of 100m and more, at frequencies of several hundred MHz. Then again, a decent coax cable like RG6 has virtually no loss up to 1GHz over distances you'd encounter around the house. Impedance matching may also be a problem with Cat-6, I don't think it has a very predictable impedance.

Wouldn't work.At least not above the level of a "coat hanger" as antenna which means you may get lucky here and there and actually pick something up but not what anyone would actually call a good signal.

A "on air broadcast" signal from an antenna (either FM signals or UHF-VHF TV) must be matched to the line impedance of that antenna and that means either a balanced 300 ohm line or an unbalanced 75 ohm coax line.so while CAT-5 works as a transmission line for high bandwidth data streams and because of the topology with good (hopefully) noise rejection it is way out of spec on the impedaqnce side of things for antenna/receiver input matching

I imagine on the "If I WANT To I CAN and I will MAKE it work !" theory one could probably weasle up an amplified impedance converter at the antenna end to match the CAT-5,send the signal downline (Attenuation of the CAT-5 seems minimal at least) then at the receiver input a "down converter" type receiver that would convert the signal back to a recocnizable 75 or 300 ohm feed.

bottom line is you can make anything into a signal conduit if you use conversion techniques (like the AC riders ince used to strean audio over household mains wiring) but is it the best solution all things considered ?

Especially when you already have a plethora of well designed RF based on-air broadcast antennae,amplifiers.splitter/combiners to choose from...

As for the audio signal transmission side of things (interlinks) it has been my habit to use simple non-shielded "tiny wire" twisted pairs and/or triple braids like the Kimber PBJ for local componant interconnection being careful not to come close to any mains AC or if I have no choice to cross the line at a right angle to minimize mutual conductance unless the next stage is one that either has high gain or is located a far distance away.

For high gain feeds where noise pickup must be way minimized or it will be audible due to the high gains also amplifying any noise I have for years used Mogami Neglex (star quad type) in the unbalanced 2+2 "turnatable end only" shield connection for turntable to phono stage interconnect and for mics in the balanced mode with the shield connected at both ends as per the spec.I avoid any potential problems here by having both a "ground-lift" switch on all balanced inputs plus true-balanced-transformer isolation.

For very long runs,that would be for me anything over 10ft,I have come to the conclusion after trial and error that there is really little need for balanced lines if the cable uses an outter shield (again connected at the "send" end only) as long as you have enough DRIVE to push the signal along the cable and you use common sense impedance matching so I use both unbalanced 600 ohm transformer coupled send/receive type interfaces and more typical consumer level unbalanced 150 ohm line driver/cable/10K receiver.

Both work well for me with the 600 ohm line better at noise rejection due to the lower impedances used at the receiving end where the combination of high-Z's and solid state circuits can n some cases make for a dandy RF receiver ;D

[dotnet]

Jul 1, 2008 14:35:06 GMT rickcr42 said:

A "on air broadcast" signal from an antenna (either FM signals or UHF-VHF TV) must be matched to the line impedance of that antenna and that means either a balanced 300 ohm line or an unbalanced 75 ohm coax line.so while CAT-5 works as a transmission line for high bandwidth data streams and because of the topology with good (hopefully) noise rejection it is way out of spec on the impedaqnce side of things for antenna/receiver input matching

Yes, I thought so. Cat5/6 cable has a nominal impedance of 100 ohms, but there is no requirement for impedance matching at the termination, and the actual impedance fluctuates by at least +/- 20% over the frequency range (http://www.belden.com/pdfs/quality/Cat6_5.pdf). Even if one would replace the 300-to-75 ohm transformer with a 300-to-100 one, it would still be hit and miss.

Cheers
Steffen.