On Aug 30, 11:12*am, InfRes wrote:
Hi,

I've noticed most homebuilt amateur antennas use tubing and usually
copper,
whereas commercial antennas typically use round bar, either steel or
Aluminum.

I understand the advantages of the materials in terms of electrical
conductivity and weather resistance,
however I dont understand the pro's and cons of using tube vs round
bar? Can you point me to
a book that may discuss this?

Have studies been done re the effect of a layer of oxidation on the
performance of the antenna?

Finally, there is plenty of material about designing antennae for a
band, but every little about designing it at a particular impedence,
can you point me to a discussion on this too?

Copper has the advantages that copper pipe and fittings are available
at any hardware store or home improvement store. Aluminum isn't
exactly rare but it's not so easy to find in your hometown on a Sunday
afternoon at a retail store.

Copper is also easily joined with solder by just about anyone using
very simple tools. Aluminum can be welded but this requires more skill
and a welding machine.

Aluminum is a superior antenna material in terms of strength per
dollar or strength per weight, but not quite as readily available.

Very few aluminum antenna designs use solid bar, with the exception of
VHF/UHF or tips where the elements are so skinny that there's no point
to making them hollow. The vast majority of HF aluminum antennas are
not solid bar but nested sections of aluminum tubing. The ham radio
magazines have lots of ads in the back from places that sell nesting
aluminum tubing sections.

I don't think there is any substantial electrical difference in copper
vs aluminum oxidation. Play with EZNEC varying the conductivities and
you'll find that the conductivity changes are in the noise.

One important thread in these antenna designs, is not that they are
numerically superior in performance to some other technique. It's that
they're buildable by average hams using readily available materials.

Tim.