Since this topic has been recently discussed, I was wondering how well
EZNEC (ver. 4+ here) would model a wire antenna made with stainless
steel wire. The "Wire Loss" table in EZNEC allows a User Defined
Resistivity and Relative Permeability. Would the fact that SS wire is
usually comprised of a very large number of strands has any appreciable
effect on the loss? Assuming that EZNEC can do the modeling correctly,
what would be approximate values to use for the resistivity and relative
permeability? I did a quick measurement in a short piece of SS stranded
wire measured a DC resistance (with a 4 wire ohmmeter) of ~50 times that
of copper.

Thanks and 73,
Larry Benko, W0QE

On Wed, 25 Aug 2004 22:58:14 -0600, Larry Benko
wrote:

Would the fact that SS wire is
usually comprised of a very large number of strands has any appreciable
effect on the loss?

Hi Larry,

Below, you show you have a Kelvin Bridge capable of determining the
resistance regardless of stranding, trust your tools but know their
(and your own) limitations. Multiple strands is an asset at very low
frequencies for Litz wire - an unlikely application in this forum
(given both that stranded wire does not meet the criteria for Litz
wire, nor do the operating frequencies we typically encounter here).

Assuming that EZNEC can do the modeling correctly,
what would be approximate values to use for the resistivity and relative
permeability?

Only you are in a position to determine its ferromagnetic
characteristic, at least to a first pass (of the magnet)
approximation.

I did a quick measurement in a short piece of SS stranded
wire measured a DC resistance (with a 4 wire ohmmeter) of ~50 times that
of copper.

Seems like a suitable clue. It could be a greater problem if you
built it into coils, although it may enhance the antenna's efficiency
per unit length through circular radiation endowed by powerless
acceleration in counter-anti-clockwise constant simultaneous phase
changes.

73's
Richard Clark, KB7QHC

Larry Benko wrote:
Since this topic has been recently discussed, I was wondering how well
EZNEC (ver. 4+ here) would model a wire antenna made with stainless
steel wire. The "Wire Loss" table in EZNEC allows a User Defined
Resistivity and Relative Permeability. Would the fact that SS wire is
usually comprised of a very large number of strands has any appreciable
effect on the loss? Assuming that EZNEC can do the modeling correctly,
what would be approximate values to use for the resistivity and
relative permeability? I did a quick measurement in a short piece of
SS stranded wire measured a DC resistance (with a 4 wire ohmmeter) of
~50 times that of copper.

Stranded wire will increase the RF resistance compared to the equivalent
cross-section of solid - but a DC resistance measurement will not show
this.

In both cases the skin effect forces the RF current to flow on the
surface. The solid wire has a continuous surface, but on stranded wire
the current path has to hop from strand to strand. Because the sideways
contact pressure between strands on the surface is not very great, this
increases the resistance per unit length.

Bare stranded copper is very vulnerable to this effect, because copper
corrodes readily in the atmosphere and even a thin film of corrosion
will force the strands apart. You'd be very unlikely to notice the
gradual worsening of performance in something like an HF antenna... but
it's still there.

Stainless steel is rather an opposite case: the RF resistance of most
grades of SS is so high that stranding may not make much extra
difference, and of course it's also much less easily corroded than
copper.

What kind of wire you choose depends on your priorities. For example,
for marine use the absolute priority is that the antenna is available at
all times, so they use thick stranded phosphor-bronze for their HF
"wires". It isn't the best RF material, but it's so strong, your 80m and
40m inverted-Vs make very good tower guys.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

The analyzer post gave me an idea you may want to try out -
take equal pieces of copper and stainless wire -
Long enough so that an antenna that size would fall within capabilities of
the analyzer -
see what the ol'analyzer tells you about resonant freq for each -and
resistance for each at resonance -
then try again at different lengths and freqs - compare results
then there oughta be a publishable ratio for those freqs. - whatcha think?
please report back within the week ;-)

"Larry Benko" wrote in message
...
Since this topic has been recently discussed, I was wondering how well
EZNEC (ver. 4+ here) would model a wire antenna made with stainless
steel wire. The "Wire Loss" table in EZNEC allows a User Defined
Resistivity and Relative Permeability. Would the fact that SS wire is
usually comprised of a very large number of strands has any appreciable
effect on the loss? Assuming that EZNEC can do the modeling correctly,
what would be approximate values to use for the resistivity and relative
permeability? I did a quick measurement in a short piece of SS stranded
wire measured a DC resistance (with a 4 wire ohmmeter) of ~50 times that
of copper.

Thanks and 73,
Larry Benko, W0QE



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