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Re: [TowerTalk] solid THHN vs jacketed copperweld

To: towertalk@contesting.com
Subject: Re: [TowerTalk] solid THHN vs jacketed copperweld
From: "Lux, Jim" <jim@luxfamily.com>
Date: Tue, 27 Sep 2022 16:39:04 -0700
List-post: <mailto:towertalk@contesting.com>
On 9/27/22 4:04 PM, Steve Maki wrote:
Thanks Jim.

I know this is a scenario of diminishing returns...how many skin depths does one shoot for?
That's an interesting question.  It has to do with the fraction of 
current in the "skin".  If you've got 5 skin depths, then almost all of 
the current is in the copper. The current density goes as 
exp(-d/skindepth) and exp(-5) is 0.007 - so 99.3% is flowing in the top 
5 skin depths.
But as microwave people plating gold over nickel have found, if you're 
at the 1 skin depth, then you're only down to 37% at that level, so a 
fair amount of the current is flowing in whatever is underneath. And if 
"underneath" is ferromagnetic, then the skin depth in *that* is really 
tiny, so all the current is flowing in a tiny area, so the loss is high.
For 2 skin depths, you're down to 86.5%, and 13.5% is in the 
underneath.  That's like 0.6 dB, if you assume all the 13.5 is loss.


Note: this doesn't even get into "round" conductors. As long as skin depth << diameter, then you can treat it as a flat plate.





On 9/27/2022 5:31 PM, Lux, Jim wrote:
On 9/27/22 2:22 PM, Steve Maki wrote:
I seem to recall ordering Copperweld wire, but it was a long time ago.

Just a quick note that after replacing the (insulated) #12 THHN with the same length insulated #12 "copper clad steel tracer wire", we could see no change in resonant frequency, so there seems to be enough copper cladding for my purpose at 3.5 MHZ.
There will only be an inch or so of wire exposed to the air at the 
center insulators, so that will be easy to monitor for corrosion 
over time (such as it is :-) Or I may coat the exposed wire with 
liquid tape.
73, Steve K8LX

Skin depth in copper at 4 MHz is 1.3 mils, 32 microns.


Copperweld

https://www.copperweld.com/application/files/4915/3833/2604/Welded_Copper-covered_Steel_CCS_21.pdf

21% CCS AWG 12 has 0.0808" diamter (2.05mm) with a nominal thickness of 0.0616 mm ( so about 2 skin depths at 4 MHz)

https://www.copperweld.com/application/files/7115/3833/2604/Welded_Copper-covered_Steel_CCS_40.pdf
40% CCS  has copper that is 0.2052 mm thick ( 6 skin depths)





On 9/21/2022 2:07 PM, Donald Chester wrote:
Steve Maki lists at oakcom.org Tue Sep 20 15:19:37 EDT 2022 wrote:

I had sworn off copperweld many years ago after noting that the copper
plating did not last forever.
Was that real copperweld, or was it copper-plated steel with only a 
minuscule layer of copper deposited on the surface, like the stuff 
used for electric fence wire?
Real copperweld has a thick copper jacket that is practically 
indestructible.  I use #10, salvaged from an abandoned railway 
telegraph line of yesteryear, scored free for the taking many 
decades ago.  You can beat it with a hammer or leave it buried in 
the soil (as ground radials) for years and the jacket won't come 
off unless it's deliberately removed with a file or grinding wheel.
That copper-plated junk begins to rust through in only a couple of 
years.  The copper is so thin that it probably has negligible 
benefit  from the skin effect; you are effectively using plain old 
steel wire.
Don k4kyv
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