[TowerTalk] UV and WX deterioration of THHN insulation, and effects

[jimlux]

On 12/28/16 7:49 AM, jimlux wrote:
> On 12/28/16 5:51 AM, Patrick Greenlee wrote:
>> Skin effect... If skin effect can force conduction into the outer limit
>> of the wire (the chemically altered part with poor conductivity) then
>> why doesn't the skin effect force conduction out into the insulation and
>> really have poor conduction? (or in bare wire out into the surrounding
>> air)
>>
>> My friend and guru (who refuses to post here) has been a ham for several
>> decades, is a retired EE, and has 35+ years antenna design experience
>> (his specialty) agrees with the concept that RF conductivity can be
>> characterized as a collection of parallel impedances, a continuum
>> actually.  The depth of penetration of RF in a conductor does not have a
>> "magic" cut-off point but instead has an exponential extinction.  That
>> is, the deeper into the conductor the less RF but there is no magic
>> barrier preventing RF from penetrating to any arbitrary depth, although
>> at rapidly reduced values.
>>
>
> Exactly this..
> Skin depth is a convenient way to measure the exponential fall off: it
> is the depth at which if you had a uniform slab of that thickness and
> uniform current density it would have the same resistance as an
> infinitely thick slab..
>
> That is: you can calculate the resistance by Skin depth* width * length
> * resistivity.

Oops.. resistance = length*resistivity/(skin depth * width)