[TowerTalk] KF4BWG

[David Gilbert]

I was more concerned about the proximity effect in the horse fence 
scenario ... 1.5 inches wide with eighteen 7 mil wires.  I suspect that 
is still "close-ish", which would make my calculations somewhat off ... 
although I suspect there might be an influence on "close-ish" that was a 
function of the magnetic permeability.

It's a complicated world ...   ;)

Dave   AB7E


On 4/18/2019 5:07 PM, jimlux wrote:
> On 4/18/19 4:30 PM, David Gilbert wrote:
>>
>> I do have a question for the experts about what I posted below. What 
>> effect, if any, is there on skin effect for individual wires when you 
>> have several in close proximity?  Since skin effect is a 
>> field-related phenomenon, does having multiple fields in phase 
>> mitigate the effect on the individual wires?
>>
>> Just double checking ...
>>
>
> if the wires are "close enough" then the current tends to flow on the 
> "outer surface" of the ribbon.  In the limit, a flat strap is just a 
> bunch of conductors close together.
>
> For typical ribbon cable with 50 mil spacing and 26 AWG wire (16 mil 
> diameter) - the wires are spaced about 3 diameters - that's "close-ish"
>
> Skin Depth at 1 MHz is 65 microns which is 2.5 mil (roughly)
> at 10 MHz it's 0.81 mil
>
> I'm going to guess that proximity effects are small at HF frequencies. 
> A bigger issue might be the dissipation losses in the insulation.  tan 
> d for PVC is around 0.06, which is pretty high. polyethylene is .0003, 
> PTFE is .0002
>
> OTOH, lots of people have measured the loss in zip cord, which is also 
> PVC insulation and it's not that huge.
>
>
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