[Towertalk] Re:Titanium for antennas, (was Dayton day 2)

[Jim Lux]

----- Original Message -----
From: <K7LXC@aol.com>
To: <towertalk@contesting.com>
Sent: Sunday, May 19, 2002 5:45 AM
Subject: [Towertalk] Dayton day 2


>     A couple of more observations. There was a company who will be
> introducing titanium yagis. Their claim is that the antennas will not
corrode
> and they will be practically indestructible. For those guys with hostile
> environments, they may be worth the additional 30-50% cost factor. We'll
have
> to see what designs they come out with. I don't know if they'll make the
> titanium itself available.

Titanium is probably a non-optimal material for antennas... Depending on
alloy, etc. it forms a fairly thick semiconductive oxide layer, unlike
aluminum, where the oxide is a good insulator, and thin to boot.  Granted,
they might be passivating the surface with some appropriate treatment.

Ti (in the usual high strength forms available) is also a royal pain to work
with... Just try drilling or cutting it with conventional tools.

Yes, Ti is quite strong on a strength for weight basis (esp compared with
steel.. twice as strong, half the weight), but, consider what this means for
an antenna...  To take advantage of this, you have to have thin elements (to
get the mass down), which, in general, makes for poorer practical antenna
performance (i.e. the antenna will likely have narrower bandwidth). A thin
Ti element, while being of the same yield strength as a Al element (i.e. the
load at which it fails), might actually be less stiff, and move more in
wind, gravity, etc. Ti is a lot more dense than Aluminum (4.5 vs 2.7 (steel
around 7-8))

All things considered, aluminum makes a pretty good material for antennas...
If you need more performance, some form of plated composite might actually
be a better deal (say, silver plated carbon fiber composite?.. Silver oxide
is a good conductor, after all, and carbon fiber composite is very strong
(for mass) and very stiff (good dimensional control))  I'd also think, off
hand, that on a dollars per strength issue, aluminum is much cheaper than Ti

Titanium is something you use when you need it's unique properties, a very
strong but small component (i.e.a  highly loaded small bolt) or something
that won't corrode even if gouged,  good strength at high temperatures (i.e.
skin of SR-71) etc.

For corrosion resistance, I'd guess that properly passivated aluminum will
be cheaper than titanium, any day, and a heck of a lot easier to work with.
Anodizing is a pretty inexpensive process, and, there's also paint and
powder coating.  One should also bear in mind that most corrosion comes from
galvanic effects from dissimilar metals, so to get the benefits of Ti,
you're going to have to use all Ti hardware, insulating bushings, etc.