On 10/13/2014 11:44 AM, John S wrote:
On 10/13/2014 9:12 AM, Ralph Mowery wrote:
"Lostgallifreyan" wrote in message
. ..
"Ralph Mowery" wrote in
:

Looking at a chart in an old ARRL antenna handbook gives a rough
estiment of a length of 500 feet and a tension of 400 pounds a wire of
around 12 to 14 gauge will drop about 10 feet if Idid it right.


That's useful. Thanks. Did they say what metal it was? I'm guessign hard
drawn copper but if not it may be harder to adjust reckoning for
something
else.

They gave two types. Hard drawn copper and copper coated steel. The
only
differance would be the weight of the wire and how much tension you
can put
on the wire before reaching the breaking point. The type of wire does
not
matter, just the weight and how much tension you can put on it before it
breaks.

(snip)

My recollection is that copper-coated steel should not be used below a
frequency where the skin depth is less than a few times the copper
coating thickness. So, there is a minimum frequency vs copper thickness.


A good rule of thumb. But even at 1Mhz, the skin depth is about 66
micrometers (and falls with the square root of the frequency - at 10Mhz
it's about 21 micrometers). Cladding over a ferromagnetic material
increases the skin depth slightly, but we're already talking pretty
small figures here,.

Where it DOES come into play is when you run DC through the coax, also.
For instance, this is common in the satellite TV arena, where DC is fed
over the coax to power a preamp at the antenna. There you need to use
solid copper. But for most ham use, copper clad will work just fine, as
long as you stay within the power rating of the coax.

One side note. Copper clad anything is not certified for any ethernet
cables. Even though ethernet runs at very high frequencies, only solid
or stranded copper is acceptable.

Normally I don't recommend Wikipedia for technical discussions, but
http://en.wikipedia.org/wiki/Skin_effect is a pretty good article on it
and explains it much more clearly than my old physics textbooks did.

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