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Author Topic: Antenna wire material question  (Read 3352 times)
N0SOY
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Posts: 72




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« on: June 10, 2012, 03:02:27 PM »

I am trying to build a VLF antenna for a research project.  Since copper wire prices  has gotton out of control I have though of using Aluminum electric fence wire for the antenna and loading coil.  It is for a reciever only.  Will the difference in the resitance create much reduction or will it work well. 

Thanks

David
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W3MR
Member

Posts: 14




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« Reply #1 on: June 10, 2012, 03:59:42 PM »

If you are planning on having the antenna and loading coil last more than one year, use copper.  I have had the aluminum fence wire disintegrate after several years up as an antenna.  For the loading coil, I would use copper.  The difference in the copper vs aluminum resistance will not make any difference.
Mel W3MR
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WB6BYU
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Posts: 13243




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« Reply #2 on: June 10, 2012, 08:02:53 PM »

I have had an antenna up using aluminum electric fence wire for nearly 10 years.  It still
works fine.

Yes, aluminum has a higher resistance.  In most cases this isn't a problem, but it can
be if your antenna has a very low radiation resistance (as may well be the case at VLF.)
For example, if using copper wire your coil and antenna had a DC resistance of 10 ohms,
and the radiation resistance was 1 ohm, your efficiency would be 9%.  With aluminum
the resistance would be roughly 50% higher, so 15 ohms, and your efficiency would
drop to 6%.  This probably isn't the end of the world, and in most cases the signal-to-
noise ratio wouldn't change, but it certainly is something to include in your calculations.

On the other hand, if switching to aluminum allows you to use a larger wire for the
same or lower cost, then the total RF resistance may actually be lower, depending on
the wire size relative to the skin depth at the operating frequency.


The main problems using aluminum have to do with wire corrosion, especially due to
dissimilar metals when connecting it to a copper feedline.  Use an anti-corrosion paste
(such as Ox-Gard or No-Al-Ox, available in the electrical department of the local
home improvement store) on all joints, and try to avoid joining copper to aluminum
wherever possible.  Usually I'll use a stainless steel bolt, washers and nuts, with a
washer separating the copper and aluminum wires so they don't actually touch.

On the other hand, copper wire is available in many different sizes, and it might be
that a coil of #26 or so copper is more practical than the smallest size of electric
fence wire.  That depends on the specifics of the coil and antenna that you are
planning to build.
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K9KJM
Member

Posts: 2415




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« Reply #3 on: June 10, 2012, 10:14:30 PM »

I have had very good luck using electric fence wire for antennas.   Both galvanized steel, And aluminum.

The trick to long life aluminum outdoors is to keep it OUT and away from the soil.   Around here, Aluminum in the air will last for many, many years.   It will turn to white powder within a year or so if allowed to touch, Or get into the soil.

Remember if you mix copper and aluminum to use some kind of antiox compound on the transition joint!
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N2EY
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Posts: 3879




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« Reply #4 on: June 12, 2012, 01:26:07 PM »

For receiving it won't make a difference.

The big issue is that you can't easily solder aluminum

73 de Jim, N2EY
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K8AG
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Posts: 351




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« Reply #5 on: June 14, 2012, 07:53:23 AM »

Copper wire antenna under tension supported end to end.  Ten + years here so far.

73, JP, K8AG
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W6EM
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Posts: 791




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« Reply #6 on: June 15, 2012, 07:35:28 PM »

Since no one has mentioned copperweld yet, I'll toss in my two cents.  Superior strength, but stiff.  A thin layer of copper is plated onto a steel wire.  Easily soldered.  Only real problem with it is you don't want to nick it as it can corrode the steel if the nick gets/stays wet.  Less than solid copper in price and won't elongate over time or work harden at terminals and snap like soft drawn copper can.

The trick with using aluminum is to make a transition connection with a metal that has a corrosion potential closer to it than copper.  Like stainless.  Another good choice is tinned copper.  (tin the metal, not covered with solder).  Tin is also close in corrosion potential to aluminum.  With any aluminum wire, you need to first clean off the surface oxide with sandpaper or steel wool and immediately apply a good anti-oxidant grease to keep it from re-oxidizing before you connect it via stainless hardware.  A fairly inexpensive connector that is UL listed for connecting copper and aluminum is something called a "split-bolt" connector.  The ones that can be used are tinned as opposed to bare copper and have "AL-CU" stamped on the sides and they come in various AWG wire size ranges.

If aluminum wire is lying against moist soil or a different metal and moisture is present for a while, there will probably be corrosion.  The aluminum forms aluminum hydroxide, a non-conductive white powder.  Keep it insulated, prepare it and terminate/connect it to stainless or tinned copper carefully and you won't have a problem.

73.

Lee
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WB6BYU
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Posts: 13243




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« Reply #7 on: June 16, 2012, 07:28:27 AM »

Quote from: W6EM

Since no one has mentioned copperweld yet, I'll toss in my two cents.  Superior strength, but stiff.  A thin layer of copper is plated onto a steel wire...



Genuine CopperWeld(r) is 30% copper, 70% steel.  That's not just a "thin layer" of copper plate.
It is referred to as "copper clad wire".  But many hams get confused and use copper plated welding
wire instead, which has a very thin layer of copper that can quickly corrode off.

At VLF the copper thickness is important due to the deeper skin depth than at higher frequencies.
You certainly don't want to use stranded CopperWeld(r) - it can even get lossy on 80m and 160m
because the total copper thickness is less.  But at least on VLF the losses of the underlying steel
aren't as bad as they are at higher frequencies.

CopperWeld(r) isn't a bad choice for antennas that have to cover a long span.  But if your
antenna is electrically short (as it likely will be at VLF) the radiation resistance will be low,
and the losses may be more important.

However, you asked about winding coils.  Unless they are relatively large in diameter, the
CopperWeld(r) will be a royal pain to work with, as it is very springy.

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KR4HV
Member

Posts: 6




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« Reply #8 on: June 22, 2012, 11:06:48 PM »

Most all (but probably not all- for those waiting to jump) beam antennas are made from aluminum tubing.  Most all, but probably not all, mobile antenna whips are made from stainless steel.  Most all, but not all, (some cities still use copper for some distribution lines- they turn green and you can see that.) use electrical transmission line made from aluminum strands wound around a steel messenger.

There are crimp and screw connectors/lugs made for aluminum or copper connections.  You can buy them at any good electrical supply house.  Use some Penetrox on the connections.

So, if  solid aluminum wire will take the tension loads from the trees or other supports and winter ice, if it occurs at your QTH, and you have aluminum wire already, by all means use it and give it a try. If you are going to buy it, get a size or two larger wire to compensate for the difference in current capacity (if that is an issue but probably not) and if you feel the need, to compensate for the (small effect in this case) conduction differences.

Aluminum wire will work harden from flexing but so will copper and hard drawn copper.  It will also corrode but so will copper.

I prefer and use copper wire for antennas but  solid aluminum wire should work just as well if it doesn't break in your particular application.  Otherwise DXers would opt for copper beams.  Wink The ham at the other end will never know you are using it.

Besides, you could have made several QSOs with aluminum wire while this discussion is going on.  Grin

73, Walt
KR4HV

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KD4LLA
Member

Posts: 457




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« Reply #9 on: June 23, 2012, 07:12:13 PM »

I am trying to build a VLF antenna for a research project.  Since copper wire prices  has gotton out of control I have though of using Aluminum electric fence wire for the antenna and loading coil.  It is for a reciever only.  Will the difference in the resitance create much reduction or will it work well. 

Thanks

David


Well how long will the research project be going on? One year, two, or more?

I was bush-hogging weeds on my farm today and came across plenty of fence that was put in by my Grandfather over forty years ago, and it was steel!

Try the electric fence wire and report back here how well it worked for you?  Or experiment with both aluminum and cooper and then tell us which is better and why?

Mike

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W6EM
Member

Posts: 791




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« Reply #10 on: June 25, 2012, 09:16:08 PM »

Quote from: W6EM

Since no one has mentioned copperweld yet, I'll toss in my two cents.  Superior strength, but stiff.  A thin layer of copper is plated onto a steel wire...



Genuine CopperWeld(r) is 30% copper, 70% steel.  That's not just a "thin layer" of copper plate.
It is referred to as "copper clad wire".  But many hams get confused and use copper plated welding
wire instead, which has a very thin layer of copper that can quickly corrode off.

At VLF the copper thickness is important due to the deeper skin depth than at higher frequencies.
You certainly don't want to use stranded CopperWeld(r) - it can even get lossy on 80m and 160m
because the total copper thickness is less.  But at least on VLF the losses of the underlying steel
aren't as bad as they are at higher frequencies.

CopperWeld(r) isn't a bad choice for antennas that have to cover a long span.  But if your
antenna is electrically short (as it likely will be at VLF) the radiation resistance will be low,
and the losses may be more important.

However, you asked about winding coils.  Unless they are relatively large in diameter, the
CopperWeld(r) will be a royal pain to work with, as it is very springy.



Perhaps you ought to familiarize yourself with fushicopperweld's specs.  They make several different combinations of equivalent copper ratios.  One with 21% overall conductivity of the same AWG size copper is used for CATV drops.  But, that doesn't mean the fraction of copper to steel is 21%.  Or, for 30% conductivity CCS either.  They are spec'ed in conductivity ratios, not in ratios of copper to steel.

For example, their 21% data shows for an overall AWG 14 CCS wire with a cross sectional area of 1.8433 sq. mm, the actual copper area is about .243 sq. mm., or about a 13% actual ratio of copper cross sectional area to steel area.  Pretty thin.

QED.

By the way, there are all sorts of aluminum/steel combinations as well.  And some aluminum alloys that are quite strong as well.  Alumoweld (like copperweld), and in stranded configurations, an Alumoweld core wire with all aluminum strands surrounding it (AWAC).  The older reinforced stranded aluminum with a steel core, called ACSR (aluminum conductor, steel reinforced) had problems.  Corrosion of the aluminum.  Again, a galvanic action between the steel and aluminum when wet.  The steel core wire was at times galvanized or just coated with grease, or both, to try to limit the corrosion.  AWAC was the best approach, though, offering superior strength and high conductivity.
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