[SI-LIST] Re: Main attenuation effect of long cables
- From: steve weir <weirsp@xxxxxxxxxx>
- To: cchalmers@xxxxxxxxxxx, "SI-List" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 06 Aug 2004 02:32:26 -0700
Chris,
Assuming that you mean either 100Mbps or 200Mbps NRZ coded wires, skin
effect is the dominant loss and is set by the wire gauge. The specs for
Cat5e and Cat6 define loss / meter at any given frequency. GigE / Cu has
signal components in your range.
For S/N budget, you are primarily fighting loss and NEXT as the dominant
noise source.
Shielding done properly will reduce your EMC headaches. Without shielding,
you will need very good CM filtering.
Steve.
At 08:30 AM 8/6/2004 +0100, Chris Chalmers wrote:
>Si list,
>
>With standard 100ohm twisted pair cable (such as cat 5e or cat 6)
> when they reach high frequencies (100MHz) at 10Metres, what is the
> main factor that causes the attenuation. Here are some options,
>
>1. The AWG of the conductors
>2. The dielectric properties (if the pairs are enclosed)
>3. Transmission line effects, reflections
>4. Crosstalk, NEXT, FEXT.
>5. Noise pickup.
>
>The signal transmitted would be LVDS.
>
>Also I have read Doug Smiths excellent note on the comparison
> of the EMC performance of shielded versus unshielded cables.
>Does any one else have views on whether its worth using a shielded
> cable for 100ohm twisted pair data transmission?
>
>
>Any help would be much appreciated
>
>Thanks in advance
>
>Chris
>
>
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