Shielded Cable Effectivness

[danger_85]

Hi all,

Just wondering what are the key specifications to look for in shielded cabling. ie: what are the values that tell me it is a well shielded cable compared to a poorly shielded cable.

Cheers
Danger

 

[Leftyretro]

Hi all,

Just wondering what are the key specifications to look for in shielded cabling. ie: what are the values that tell me it is a well shielded cable compared to a poorly shielded cable.

Cheers
Danger

Belden cable site has a lot of technical papers, I'm sure you can find as much as you want and then some.

**broken link removed**

Lefty

 

[Papabravo]

I'm not sure you can make this determination from specifications alone. It helps to know what shielding can and cannot do for you, along with some idea how to measure the effectiveness. Radiated emissions, are different from electrical fast transients, are different from conducted noise. After twisting the signal pairs shielding may not do much for you, it all depends on the application and the environment.

 

[HiTech]

Like Papabravo said. It also depends on what the application is for that cable. For example, rf bandwidth requires very high quality shielding, typically consisting of 100% braid and a foil wrap as well. Any good cable worth it's cost will designate the shielding on its vinyl/poly jacket.

 

[audioguru]

I cut the RCA plugs off a shielded audio cable from RadioShack.
The shield wasn't braided, and it wasn't foil. It was just a few strands of fine wire wrapped loosely around the insulated center conductor. The poorest shield I have ever seen! It actually attracted hum.

 

[HiTech]

You'd be surprised at how many so called quality audio cables with gold ends are actually lousy and not worth the money spent. Gold ends do nothing to improve signal connectivity unless gold is used throughout the entire signal path. I too have seen "shielded" audio cables that are nothing more than 10 strands of micro-fine wire twisted around the center conductor. No wonder they break easily at the molded in strain reliefs... if you can even call them that!

 

[Dean Huster]

That last place you want to buy coax from is Radio Shack. As mentioned, cable with a braided shield such as RG-58 is only about half there. Good cable has the shield braid wires snugged next to each other. RS's cable shields are more like the lattice around your porch. Once you have conductive Mylar shield around the cable (and usually a drain wire) such as the typical RG-59 or RG-6, you have 100% shielding. Before the foil shields, you could get very expensive double-shielded cable that typically had two good close-packed shields around the center conductor, some with the shields insulated from each other, others with the shields in intimate contact. And the wire was silver-plated when the military bought it.

Dean