Topband: Aluminium antenna wire

[Pete Ferrand]

Hi Tom:


> Does anyone have any experience of using alumin(i)um wire for 
> antennas? 

Speaking from the perspective of long experience with aluminum antenna
wire (three weeks) I'd say it works very well. It handles a lot
differently than copper. 

I wanted to give it a try since the hard drawn single strand copper I'd
been using since 1983 was tired, and I wanted to experiment a bit. I
bought a quarter mile of #14 for $24 at the local farm store and wound
up using 900 feet, including the two buried ground wires under the
elements, the Vee beam with 200 foot elements and the 40 foot open four
wire feedline, plus wasting some in just playing around with it. 

Unfortunately I don't have tall trees here, and the ends are supported
on very old apple trees. The weight reduction is remarkable, and that is
a consideration since trees will only support so much.

I have extensive experience with tall whippy trees elsewhere and
relatively successfully with the hard drawn copper. The main requirement
is that all junctions be designed for extreme flexing, which means the
wire ends in a large loop and the connection made with some kind of
braid that can flex. I also used rope that stretches. 

I have some concern about the ability of the aluminum to handle flexing
since but I imagine it's designed to handle movement to some degree,
since an electric shock won't stop the occasional ox from walking into
it.

In your case, and if/when this system breaks, I suggest to a catenary
system where there will be a rope (non water absorbing) supporting the
wire and taking the stress. I've used this in the past and it worked out
ok.

Connecting to aluminum is problematic, and I solved it in two ways. I
bought some aluminum brazing rod from the local hardware store and used
that, although I had to use the old scrub-oiled-wire-with-abrasive to
get it to work; the flux didn't. The brazing rod's melting point is very
close to that of the aluminum wire so some experiments are needed. What
I found odd is that I could melt two pieces of the wire with a small
propane flame but they can't melt together.

I also used screw type connectors that are "dual rated", meaning Cu and
Al, from the hardware store. Mine are made by Thomas & Betts and a pair
of them was $1. It's a small machined aluminum block with a setscrew
type screw. My original thought was to use these as the Al to Cu
transition, but as things worked out there never was one and the Al just
goes directly the antenna matcher. I designed the system for a minimum
number of connections, meaning that each element of the Vee and its side
of the feedline are one piece of wire.

I am not especially concerned about aluminum's level of resistance,
considering that the hard drawn copper I'd been using has a
significantly higher resistance than pure copper anyway, and no one ever
cared about that. And aluminum is used for electrical transmission lines
and all beam type antennas, I figure the difference is small.

We have not been blessed with dramatic temperature changes yet so I've
no idea how the tuning will be affected by that.

Hope this helps a bit.

73,
-Pete
WB2QLL
Somers, WI







> My 160m antenna is supported by tall trees which 
> tend to move in opposite directions with the wind and the 
> antenna life expectancy using multi-strand copper is short! I 
> bought a 400 metre reel of 1.6mm Al wire from the local farm 
> supplier for 20 quid (35 dollars). Resistance is specified as 
> 0.065 ohms/metre.
> 
> Tom G3OLB 
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