Antenna wire
 

In searching the 'net for wire suitable for wire antennas, I came
across a single core 2.7mm diameter 40% aluminium clad high tensile
steel wire.

I am trying to get some further detail on its Guaranteed Breaking
Strength, but my guess is that the steel core is probably somewhere
about 1000 MPa UTS, and will give an overall GBS around 4kN.

The coating thickness looks like high conductivity aluminium, with a
thickness of 300 microns, which is 5 skin depths at 1.8MHz, so
conductivity should be good.

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Owen
--

Antenna wire
 

On Wed, 23 Aug 2006 02:18:21 GMT, Owen Duffy wrote:

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Hi Owen,

I've used ordinary house wiring for long-wires and they have survived
100# limb falls that ripped out my matching box from its post. The
survival was with the wire, not the box.

[warning to Reggie, the prose that follows contains literary
allusions]
What price tensile strength?

The worst thing you can do is pull a wire tight in an attempt to
totally eliminate sag. The inverse sine angle of its depression
magnifies the stress by huge amounts. A slight sag will never yield a
tensile failure in the most pedestrian of wire.

73's
Richard Clark, KB7QHC

Antenna wire
 

On Tue, 22 Aug 2006 20:04:24 -0700, Richard Clark
wrote:

On Wed, 23 Aug 2006 02:18:21 GMT, Owen Duffy wrote:

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Hi Owen,

I've used ordinary house wiring for long-wires and they have survived
100# limb falls that ripped out my matching box from its post. The
survival was with the wire, not the box.

I think "ordinary house wire" may be aluminium, a by product of 110V
utilisation I guess. House wiring here is still principally copper.


[warning to Reggie, the prose that follows contains literary
allusions]
What price tensile strength?

The worst thing you can do is pull a wire tight in an attempt to
totally eliminate sag. The inverse sine angle of its depression
magnifies the stress by huge amounts. A slight sag will never yield a
tensile failure in the most pedestrian of wire.

Subject to more reliable information on the wire's GBS, my initial
calcs are that a span of 40m (half of a half wave dipole on 160m)
would need 3.3% sag (~1.4m) to survive wind at 60m/s with a safety
factor of 3.5. Yes, of course, the mountings must also survive the
wind, and this analysis assumes not deflection of the mounting points
and no stretch of the wire.

The only thing that compares on strength and conductivity is
Copperweld, but it is not easily obtained here... I suspect the cost
of freight might double or triple the price of a 100lb pack of 30% #12
wire.

I did look at heavy galvanised wires, but it seems the move has been
to Zinc/Aluminium alloy with an overall synthetic coating, and since
it erodes much slower, the coatings are only 10 to 20 microns... not
thick enough for good conductivity.

My usual supplier looks like he can't do 3mm HDC economically any
more, hence the search.

Owen
--

Antenna wire
 

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Owen
--



I've seen comments suggesting that steele core wire is not a good idea
if you live in any kind of humid climate..... the cover clad develops pin-
holes over time which allows moisture to start the rust process of the
inner steel core. Breakage soon follows..... The comments I received
were regarding copper clad, though. I don't know if aluminum would have
the same potential problem or not.


Ed K7AAT

Antenna wire
 

On Wed, 23 Aug 2006 03:35:44 GMT, Owen Duffy wrote:

I think "ordinary house wire" may be aluminium, a by product of 110V
utilisation I guess. House wiring here is still principally copper.

Hi Owen,

Aluminium/um house wiring here was but a brief, failed experiment some
30-40 years ago.

Subject to more reliable information on the wire's GBS, my initial
calcs are that a span of 40m (half of a half wave dipole on 160m)
would need 3.3% sag (~1.4m) to survive wind at 60m/s

With a Category Four Hurricane roaring outside, I would think you
would be worried about more than wire.

with a safety
factor of 3.5. Yes, of course, the mountings must also survive the
wind, and this analysis assumes not deflection of the mounting points
and no stretch of the wire.

My wire tables offer that 40M of #12 wire would weigh 2.6 pounds in
bare copper. The breaking load would push beyond 100 times that at
337 pounds (40% copper clad is slightly more than twice that).

For a sag of 1.4 meters in 20 meters would be an angle of depression
of 4°. If I take the inverse of the sin( 4°) it would multiply the
weight by 14.3 for a tension of 37 pounds. The wire by itself would
hardly constitute any jeopardy, but there is still a choke and
transmission line's weight to be added (and I probably missed this by
a factor of two in simply winging the math).

Let it sag 3 meters and the multiplier drops to less than 7.

The only thing that compares on strength and conductivity is
Copperweld, but it is not easily obtained here... I suspect the cost
of freight might double or triple the price of a 100lb pack of 30% #12
wire.

I did look at heavy galvanised wires, but it seems the move has been
to Zinc/Aluminium alloy with an overall synthetic coating, and since
it erodes much slower, the coatings are only 10 to 20 microns... not
thick enough for good conductivity.

At something like 4 dB additional loss, this may matter. Additional
sag would seem to be a very efficient return on investment in
comparison to the additional 1.6 meters proximity to earth (that
wouldn't nearly add 4 dB loss, would it?).

My usual supplier looks like he can't do 3mm HDC economically any
more, hence the search.

Try using a rope runner.

73's
Richard Clark, KB7QHC

Antenna wire
 

On Wed, 23 Aug 2006 00:17:25 -0700, Richard Clark
wrote:

On Wed, 23 Aug 2006 03:35:44 GMT, Owen Duffy wrote:

I think "ordinary house wire" may be aluminium, a by product of 110V
utilisation I guess. House wiring here is still principally copper.

Hi Owen,

Aluminium/um house wiring here was but a brief, failed experiment some
30-40 years ago.

Hi Richard,

Thankfully, it didn't come here. I just Googled for "aluminium house
wiring fires" and got 1,080,000 hits, whereas for "copper house wiring
fires" I got 736,000 hits. I guess there may have been an issue.

Subject to more reliable information on the wire's GBS, my initial
calcs are that a span of 40m (half of a half wave dipole on 160m)
would need 3.3% sag (~1.4m) to survive wind at 60m/s

With a Category Four Hurricane roaring outside, I would think you
would be worried about more than wire.

with a safety
factor of 3.5. Yes, of course, the mountings must also survive the
wind, and this analysis assumes not deflection of the mounting points
and no stretch of the wire.

My wire tables offer that 40M of #12 wire would weigh 2.6 pounds in
bare copper. The breaking load would push beyond 100 times that at
337 pounds (40% copper clad is slightly more than twice that).

For a sag of 1.4 meters in 20 meters would be an angle of depression
of 4°. If I take the inverse of the sin( 4°) it would multiply the
weight by 14.3 for a tension of 37 pounds. The wire by itself would

Using that approximation, shouldn't you have taken the weight of a
half span? Then, isn't that weight evenly distributed over the half
span, so you should halve it again?)

A parabolic approximation is better than the triangular approximate,
and it would suggest tension is W*S^2/sag/8 or 0.28*40^2/1.2/8 N or
46.7N (~10.5lbf) which is a small fraction of the GBS of 1350N for
HDC, so yes, the wire is easily able to support itself. Wind forces
are much greater, and wind at 60m/s (highest design speed for
non-cyclonic localities under building standards here) loads the wire
to 386N (which is GBS/SF). The lowest design speed under our standards
is 41m/s, that results in about half the tension.

hardly constitute any jeopardy, but there is still a choke and
transmission line's weight to be added (and I probably missed this by
a factor of two in simply winging the math).

I was considering a span with no concentrated loads (it is a quarter
wave, half of a half wave dipole).

Yes to missing a factor or two. It is too late to be grinding numbers
on your side of the world!


Let it sag 3 meters and the multiplier drops to less than 7.

The only thing that compares on strength and conductivity is
Copperweld, but it is not easily obtained here... I suspect the cost
of freight might double or triple the price of a 100lb pack of 30% #12
wire.

I did look at heavy galvanised wires, but it seems the move has been
to Zinc/Aluminium alloy with an overall synthetic coating, and since
it erodes much slower, the coatings are only 10 to 20 microns... not
thick enough for good conductivity.

At something like 4 dB additional loss, this may matter. Additional
sag would seem to be a very efficient return on investment in
comparison to the additional 1.6 meters proximity to earth (that
wouldn't nearly add 4 dB loss, would it?).

My usual supplier looks like he can't do 3mm HDC economically any
more, hence the search.

Try using a rope runner.

Do you mean a rope as a carrier for the conductor... runs into some
other issues like differential stretch, and huge wind resistance. The
structure may stay in the sky, but the wire might be fractured anyway.

Owen
--

Antenna wire
 

COPPER-WELD

There are no issues of "reliable connections".

NOTE: Copper-weld is copper cladded steel wire. It's been used for years as a
very reliable antenna with long spans. Catenary stresses are carried by the
steel wire component.

/s/ DD

Owen Duffy wrote:

In searching the 'net for wire suitable for wire antennas, I came
across a single core 2.7mm diameter 40% aluminium clad high tensile
steel wire.

I am trying to get some further detail on its Guaranteed Breaking
Strength, but my guess is that the steel core is probably somewhere
about 1000 MPa UTS, and will give an overall GBS around 4kN.

The coating thickness looks like high conductivity aluminium, with a
thickness of 300 microns, which is 5 skin depths at 1.8MHz, so
conductivity should be good.

Apart from the challenge of making reliable connections to aluminium,
are there other "issues" that come to mind in using such wire for
antennas?

Owen
--

Antenna wire
 

On Wed, 23 Aug 2006 08:29:37 GMT, Owen Duffy wrote:

Thankfully, it didn't come here. I just Googled for "aluminium house
wiring fires" and got 1,080,000 hits, whereas for "copper house wiring
fires" I got 736,000 hits. I guess there may have been an issue.

Hi Owen,

To say the least. The problem with aluminium/um house wiring was
identified as "cold flow" where over time the mechanical joint would
fail, increase resistance and electrical failure followed. Given the
correspondence here on connecting aluminium/um, it appears that
problem has been solved by professionals, but it would also seem to
offer dim prospects in the housing industry.

Using that approximation, shouldn't you have taken the weight of a
half span? Then, isn't that weight evenly distributed over the half
span, so you should halve it again?)

No, upon further investigation, my numbers appear to be ball-park
without an order of two correction (other corrections may be
necessary).

A parabolic approximation is better than the triangular approximate,

More properly a "catenary" for sags which is a curve of constant
tension; and for our antenna use, this is a classic application. The
difference is slight in this regard as both involve hyperbolic
transcendentals, but the point of constant tension is more to be
noted. When we add the kicker of center feed weight, the curve is
obviously pulled out (which suggests linear analysis).

From my 1912 copy of "Standard Handbook for Electrical Engineers"
comes coverage of stringing power lines and calculating sag for a
given tension. Tables and calculations are not remarkably different
from my first approximation. This volume states "the working stress
should not be over one fourth this [ultimate breaking strength]."

Try using a rope runner.

Do you mean a rope as a carrier for the conductor... runs into some
other issues like differential stretch, and huge wind resistance.

True.

The
structure may stay in the sky, but the wire might be fractured anyway.

How do you come by the conclusion that the wire is destroyed, but the
rope remains?

73's
Richard Clark, KB7QHC

Antenna wire
 

Antenna wire
 

On Wed, 23 Aug 2006 11:17:37 -0700, Richard Clark
wrote:


A parabolic approximation is better than the triangular approximate,

More properly a "catenary" for sags which is a curve of constant
tension; and for our antenna use, this is a classic application. The
difference is slight in this regard as both involve hyperbolic
transcendentals, but the point of constant tension is more to be
noted. When we add the kicker of center feed weight, the curve is
obviously pulled out (which suggests linear analysis).

I think the case of a concentrated load such as a balun and feedline,
along with a distributed load is also exactly solved by a catenary,
just the ends are at unequal heights. The three dimensional nature of
the problem when horizontal wind forces are considered as well as
vertical weight forces makes solutions messy.


From my 1912 copy of "Standard Handbook for Electrical Engineers"
comes coverage of stringing power lines and calculating sag for a
given tension. Tables and calculations are not remarkably different
from my first approximation. This volume states "the working stress
should not be over one fourth this [ultimate breaking strength]."

Now that it is so easy to calculate the catenary, it is the way to
go.. but on shallow catenarys of equal height, the solution is not
much different to a parabolic one. There is still a computational
advantage to the parobolic approximation.

Standards here (aka "codes" in your country) stipulate the safety
factor to be used, and it is 3.5 for standing rigging, 5 for running
rigging. That does apply to guy wires, and seems appropriate to
antenna wires that may not also be guy wires.

I note that the ARRL takes a different approach. The ARRL Antenna
Handbook 18th edition has some information on sagging wire antenna
spans on pages 20-2ff. Similar information may be in other editions.

There is no explicit discussion of wind loading, and the design guides
(tables, nomographs, text) lead the reader to a design based on
weight loading alone and with a Safety Factor of 10 or 5 depending on
the chosen tension.

I guess that approach supports the maxim that "if your antenna didn't
blow down last season, it wasn't gib enough", or am I mythtaken!


Try using a rope runner.

Do you mean a rope as a carrier for the conductor... runs into some
other issues like differential stretch, and huge wind resistance.

True.

The
structure may stay in the sky, but the wire might be fractured anyway.

How do you come by the conclusion that the wire is destroyed, but the
rope remains?

If the rope stretches more easily than the metal conductor, it may
(depending on how it is supported) increase the tension in the metal
conductor and break it.

Owen
--