[SI-LIST] Re: Why shielded twisted-pair is still twisted?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: earl albin <earlalbin@xxxxxxxxx>
- Date: Sat, 15 May 2010 13:01:39 -0700
Earl, induced eddy currents make conductive, non-ferromagnetic shielding
work very well above the skin depth frequency.
Steve
earl albin wrote:
> I get it, trick question. A magnetic field inversely proportional to the
> square of the distance will induce a differential current into the wires
> because one wire is closer. Twisted makes the wires on average the same
> distance, same thing with an e-field. Another trick question, the external
> shield works for an e-field but not the h-field unless it's feromagnetic.
> Got a signal generator, a scope, some wire, some time. Figure it out.
> On Mon, May 10, 2010 at 3:41 PM, Neo <neoflash2008@xxxxxxxxx> wrote:
>
>
>> Hi,
>> I'm thinking about why shielded twisted-pair is still twisted?
>> Pair is twisted for controlled distance/impedance (due to twist) and for
>> x-talk reduction. If a pair is already shielded together, it is not
>> necessary to twist them any more.
>> Without twist, it will be equivalent to twin-ax cable, isn't that better?
>> Thanks,Neo
>>
>>
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>
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