Round cables vs. flat

[Edvardas]

I know that round cabpes offer better cooling possibilieties, dont block the air flow too much. But dont all those wires together interfere?

 

[sturm]

No they wont. Thats what all the extra wires are for on the 80 wire cables. Cut out electrical interferance

 

[Crashman]

Actually flat cables are better for cooling, if you flatten them out against the motherboard tray.

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[grafixmonkey]

I was told by Promise tech support that the rounded cables cause crosstalk, but I'm not sure if they were just covering their arses about their RAID cards or not. I took a transmission lines course in college, and I'd believe it if the rounded cables don't keep the signal-ground pairs together like they should. In my rounded cables, the wires seem to be all in a random jumble, which would indeed cause crosstalk if the cable is meant to use a "signal-ground" pairing with adjacent wires. The only way to tell for sure is to use equipment that I don't have access to.

 

[Crashman]

Rounded cables should used TWISTED pairs, but since it's more difficult to produce them that way, most companies don't do it. If you find a company that does, you'd probably be best off using them!

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[grafixmonkey]

I think from now on when I want to use rounded cables, I'm going to make them myself. It's so easy there's no reason not to. I just fold the cable in thirds in the middle, propagate the fold as far along the cable as I want, and put little pieces of duct tape around it. Takes about two minutes per cable, and it ends up less obtrusive than those rounded cables with their jumble of wires, metallic inserts, and big honking plastic tubes around them.

 

[Crashman]

I don't even bother. When I have a cable in the way, I fold it out of the way. If a cable has to go up to the top drive, for example, I fold it 45 degrees and lay it flat against the backpanel, so it points upward, then bring it back out toward center at the drive.

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[jiaruigoh]

hmm... but i cant do that because my flat cables are already almost at max length to reach the mobo in my huge case. so shld i get new rounded or buy new longer flat cables?

what is this twisted pair you are talking abt?

thank you for enlightening this noob

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[Crashman]

It's an old technique used mainly by SCSI cables, you twist the data cable with it's ground cable so that the inductive forces that penetrate the insulation will be absorbed by the ground cable. That way you don't need to worry about these things.

Anyway, if you have room you could simply turn your cables sideways without moving them over to the side of the case.

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[grafixmonkey]

That's pretty close, but it's more along the lines of external EM interference and how it operates on a loop of wire. If you have a loop of wire, a changing electric field will induce a voltage and current in it. If you have two wires traveling parallel to each other, it's like a really long, flat loop. Here's where the twist comes in... If you were to take the loop and flip it backwards, the interference will be the negative of what it was before flipping it. So if you twist the wires together, you essentially have many many alternating sections of "flipped" and "not-flipped" loops, and any external EM interference will tend to automatically cancel itself out because it is adding itself to the (slightly phase offset) negative of itself. It keeps the interference down as long as the interference does not originate very close to the wires and is not too high frequency.

They use it in ethernet cables too, and coaxial cable is built the way it is for a similar reason - the cylindrical ground wire that surrounds the inner wire will automatically react to an electric field such that the electric field inside the cylinder due to outside sources is zero. That leaves the wire in the middle free to carry a high quality signal for long distances without much interference.