Re: Shielding of CAT 6 cables (was Re: [tlug] FTTH ISP recommendation)

[Patrick Kellaher <kalmite@example.com>]

Edward Middleton wrote:
> jep200404 wrote:
>> Edward Middleton wrote:
>>  
>>> My point was that standard phone cables unlike category 6 cable
>>> wasn't designed for high bandwidth applications and so is not going
>>> to have adequate shielding.     
>>
>> What's the relationship between bandwidth and shielding?   
>
> Shielding causes decreased noise or increased Signal to Noise Ratio
> SNR.  For the relationship between SNR, bandwidth and channel
> capacity, from wikipedia[1]
>
>    C = B log_2(1 +(S/N))
>
>    C is the channel capacity in bits per second;
>    B is the bandwidth of the channel in hertz;
>    S is the total signal power over the bandwidth, measured in watt or
>    volt2;
>    N is the total noise power over the bandwidth, measured in watt or
>    volt2; and
>
>
> If you have a lower bandwidth cable B, like a phone cable, you need a
> higher signal to noise ratio S/N to gain the same channel capacity.
>
>> How much shielding does the CAT 6 standard require a CAT 6 cable to
>> have?   
>
> Good point, Category 6 UTP obviously has none, but it has greater
> bandwidth so can sustain higher channel capacity under lower SNR.
>
> Edward
>
> 1. http://en.wikipedia.org/wiki/Shannon-Hartley_theorem
>
Normal CAT cable is UTP (Unshielded twisted pair), so as mentioned above
most CAT cable has zero shielding.  However you can buy STP (shielded
twisted pair) which does have shielding to reduce EMI.  CAT 6 gets its
increased speed from the increased number of twists as compared to lower
rated CAT cable to reduce cross talk.

Pat