On Thu, 05 Oct 2006 23:38:11 -0700, Roy Lewallen
wrote:

I have to think about your response a bit and attempt to understand
some things a bit better. My technical knowledge is limited but I'm
learning lots.

What I have in mind, before winter sets in, is to setup a horizontal
loop just underneath the eaves of the house. Some eyes along the long
wide of the house and stretched along the narrow width. And use a
SGC Smartuner as per
http://www.sgcworld.com/SmartunerProductPage.html.

This will at least get me going on the HF side of things. Nothing
fancy and with not a lot of range but enough to give me a taste of HF
while I think about what I want to do with the trees in the lot and
such.

So one thing I would want to do is to ensure the wire is insulated
from the eyes so there is no sparking or static. And clothesline is
meant for the out of doors which is why I was thinking of it.

Tony

Roy Lewallen wrote:
Steel has a resistivity many times that of copper. It varies a lot with
the alloy, so it's not possible to put a single number on it. But the
real problem is that steel is ferromagnetic -- in other words, it has a
high permeability.

At radio frequencies, current flows in a thin layer near the surface of
the conductor. (It actually continues clear to the center of the
conductor, but the density decreases very rapidly with depth, so it's
essentially zero anywhere except very near the surface.) This
concentration of the current has the same result as passing the current
through a wire of much smaller cross-sectional area: it greatly
increases the resistance of the path carrying the current.

The problem is that the thickness of this layer (more technically, the
rate at which the current density decays with depth) is determined by,
among other things, the permeability of the material -- the higher the
permeability, the shallower the layer. So the higher the permeability,
the higher the resistance. The permeability of steel is probably even
more variable than resistivity, but I'd be surprised if you ever found
any in common use with permeability under 100. Or if you found some with
permeability of several thousand. Since the relationship between the
depth of current flow and permeability is a square root, this means RF
resistance of 10 to 100 or so times that of copper, as well as the
higher resistance due to the higher DC material resistivity.

If the antenna has a large enough surface area, even steel is fine. A
common example is an FM mobile whip, which has insignificant loss, or a
tower operated as a vertical. But because of the way the current depth
and antenna size change with frequency, the loss with a given wire size
gets greater and greater as you go lower in frequency, assuming the
antenna stays the same size in terms of wavelength. So while moderate
diameter steel wire might have insignificant loss on the higher
frequency HF bands, that same wire might have substantial loss at the
lower end of the HF range.

Most hams can measure SWR, but almost none can quantitatively measure
the strength of the signal their antennas radiate. And most run way more
power than needed to communicate, so can easily lose quite a few dB
without a major effect on communications. Consequently, the wider
bandwidth gained due to loss in steel wire is considered an asset, while
the few dB loss is probably not noticed. (Although hams spend a
staggering amount of money trying to buy a few extra dB of gain. Go
figure.) In fact, I recall an article some years ago -- in QST if I'm
not mistaken -- featuring a wide-band 80 meter antenna whose secret was
just that -- loss from using steel wire.

If you try it, you might just like it!

By the way, copper wire is easily obtained and not that expensive,
either, should you choose to go for a stronger signal rather than wider
bandwidth.

Brings up a question in my mind which is related to the points you've
made about conductivity vs. skin depth. As it then relates to bare vs.
insulated copper wire for HF work.
Bare copper wire out in the WX will oxidize which adds a layer of
copper oxide on the O.D. of the wire over time. What is the effect of
this layer on skin resistance losses at HF frequencies in practical
terms? Somewhere along the line I picked up the notion that copper
oxide is a pretty lousy conductor and the problem can be resolved by
using insulated wire for wire antennas . . comments??


Roy Lewallen, W7EL

Brian w3rv

On 6 Oct 2006 23:39:28 -0700, "Brian Kelly" wrote:

Somewhere along the line I picked up the notion that copper
oxide is a pretty lousy conductor and the problem can be resolved by
using insulated wire for wire antennas . . comments??

Hi Brian,

Consider, insulation is pretty lousy conductor too. Current is going
to conduct where it will, and ignore both insulation and oxide. Put a
high resistance path in parallel with a very low resistance path (of
identically the same length), which one will current choose? The
problem of oxide is when it encounters a poor joint and creates a
semiconductor.

73's
Richard Clark, KB7QHC

On Fri, 06 Oct 2006 05:21:00 GMT, Tony VE6MVP
wrote:

Folks

So I'm reading the 2006 ARRL Handbook page 22.6, There is a single
line stating "Steel wire is a poor conductor at RF; Avoid it." Any
idea why? Or is this just one of those physical properties?

So how much poorer than copper? Steel clothesline is easily obtained
and not that expensive. Admittedly though I haven't done much
research on copper or the other type of wires the Handbook mentions.


I am guessing that the "steel clothesline" to which you refer is
probably actually stranded (7x1?) heavy galvanised soft steel wire.

The galvanising is zinc or zinc/aluminium alloy and its thickness has
bearing on the answer for a specific frequency.

The stranding also has adverse effect on the effective RF resistance,
though not as predictable as the zinc coating.

Though it works, there are a number of mechanisms that increase the
loss, and the extent of some of them are quite difficult to predict or
to measure (for the average amateur).

The additional loss of steel wire is less important in an antenna
design that is loaded with bulk resistance, eg T2FD. A reason why
small guage stainless steel wire commonly used commercially on these
antennas isn't necessarily unsound. But that application should not
imply that small guage stainless steel is just as suited to a half
wave folded dipole.

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Owen
--

On Fri, 06 Oct 2006 22:17:10 GMT, Owen Duffy wrote:

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Sure, but clothesline wire is easily available in this small town.
Copper wire means I'd have to search it out in the nearest big city.

Tony

Tony VE6MVP wrote:
On Fri, 06 Oct 2006 22:17:10 GMT, Owen Duffy wrote:

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Sure, but clothesline wire is easily available in this small town.
Copper wire means I'd have to search it out in the nearest big city.

Tony

All the wire antennas I've built for the last 20 years or so have
been made out of electrical wire from the local home improvement
store.

They alway seem to outlive my interest in them.

--
Jim Pennino

Remove .spam.sux to reply.

On Sat, 07 Oct 2006 03:25:03 GMT, wrote:

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Sure, but clothesline wire is easily available in this small town.
Copper wire means I'd have to search it out in the nearest big city.

Tony

All the wire antennas I've built for the last 20 years or so have
been made out of electrical wire from the local home improvement
store.

They alway seem to outlive my interest in them.

Just standard household electrical wiring? So purchase some two wire
(actually three wire if you include the ground wire) electrical cable
and use the black and white wires? Will the insulation withstand the
out doors? Or do you strip off the insulation and use them bare?

Tony

Tony VE6MVP wrote:
On Sat, 07 Oct 2006 03:25:03 GMT, wrote:

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Sure, but clothesline wire is easily available in this small town.
Copper wire means I'd have to search it out in the nearest big city.

Tony

All the wire antennas I've built for the last 20 years or so have
been made out of electrical wire from the local home improvement
store.

They alway seem to outlive my interest in them.

Just standard household electrical wiring? So purchase some two wire
(actually three wire if you include the ground wire) electrical cable
and use the black and white wires? Will the insulation withstand the
out doors? Or do you strip off the insulation and use them bare?

Tony

Standard, single strand, solid, electrical wire, normally with the
insulation left on.

I usually buy blue so it blends with the sky.

Leaving the insulation on shortens the wire required ever so slightly.

The insulation lasts for years on everything I've ever put up.

--
Jim Pennino

Remove .spam.sux to reply.

Tony VE6MVP wrote:
On Sat, 07 Oct 2006 03:25:03 GMT, wrote:

Antenna wire would be one of the lowest cost elements of a complete
system, which questions the cost effectiveness of savings.

Sure, but clothesline wire is easily available in this small town.
Copper wire means I'd have to search it out in the nearest big city.

Tony

All the wire antennas I've built for the last 20 years or so have
been made out of electrical wire from the local home improvement
store.

They alway seem to outlive my interest in them.

Just standard household electrical wiring? So purchase some two wire
(actually three wire if you include the ground wire) electrical cable
and use the black and white wires? Will the insulation withstand the
out doors?

Not any of the multi-conductor household electrical wire ("Romex"),
find a spool of insulated #14 single-conductor "household wire" at any
decent neighborhood hardware store. Here in the southern provinces it's
called "#14 THHN" which comes in both solid and stranded types and in a
multitude of colors. I prefer stranded wire because it's less prone to
bending fatigue failure than is solid wire. Theoretically

If push comes to shove dial up a local electrician and ask where he
gets the stuff.

Personally I wouldn't string the wire thru bare screw eyes, I'd use the
Radio Shack catalog number 15-853 screwin insulated "TV cable
standoffs" to support it.

Or do you strip off the insulation and use them bare?

Leave the insulation alone, might get ugly after awhile but it lasts
forever out in the elements and has no discernable effect on the
performance of the wire as an HF loop antenna material.


Tony

Brian w3rv