# [time-nuts] Noise and non-linear behaviour of ferrite transformers

Didier Juges shalimr9 at gmail.com
Tue Jul 22 13:15:24 EDT 2014

```Effectiveness of coax cable (at eliminating the effects of current through the shield) is often expressed as "transfer impedance".

Didier KO4BB

On July 20, 2014 11:18:58 PM CDT, Chuck Harris <cfharris at erols.com> wrote:
>Lots of meanings to the word induce.  The one I was using was: to
>bring on, or about; effect; cause...  I was not intending to imply
>transformer action.  As an engineer I should know better than to
>try to use English to describe electrical phenomenon.
>
>My intention was to find out what: " ...the skin depth of the coax
>shield gives up well before 60Hz..." meant.
>
>Real life examples show that coax does just fine at shielding all
>the way down to DC...  As long as you keep the currents flowing
>through the outside of the shield to a minimum.  Which is done
>routinely by not connecting the ends of the shield so that current
>loops occur.  Hardly a PA system exists that doesn't have a fairly
>long bit of unbalanced shielded cable at some high impedance high
>gain input.
>
>-Chuck Harris
>
>Alexander Pummer wrote:
>> No, the current passing the outside f the shield  will not induce any
>voltage inside
>> of the coax, but the voltage drop caused by the current on the ohmic
>resistance [!!!]
>> of the shield will show upbetween the two ends of the cable -- and
>that will  show up
>> as  it was added to to the voltage which is carried on the center
>conductor of the coax.
>> 73
>> Alex
>>
>> On 7/20/2014 6:10 PM, Chuck Harris wrote:
>>> I'm not sure what you are saying.
>>>
>>> skin depth = (2.6/sqrt(fhz))inches for copper.
>>>
>>> So, at 60Hz,   skin depth = 0.336 inches.
>>> and at 100KHz, skin depth = 0.008 inches.
>>> and at 1MHz,   skin depth = 0.0026 inches.
>>>
>>> Are you saying that at 60Hz, because the
>>> skin depth is deeper than the coax shield is
>>> thick, that current passing through the outside
>>> of the shield will induce voltage inside of
>>> the shield, and that at say, 100KHz where the
>>> skin depth is a little less than the shield
>>> thickness, or at 1 MHz, where the skin depth
>>> is only a small fraction of the thickness of
>>> the shield that it won't?
>>>
>>> Or something else?
>>>
>>> -Chuck Harris
>>>
>>> Bob Camp wrote:
>>>> Hi
>>>>
>>>> The “coax is an antenna” problem comes in well before you get to
>DC. Even with no
>>>> transformer involved, the skin depth of the coax shield gives up
>well above 60 Hz
>>>> (and likely well above 100 KHz). If you want to do full isolation
>over a very wide
>>>> range you need some combination of shielding and balanced lines.
>>>>
>>>> Bob
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